This is libc.info, produced by makeinfo version 5.1 from libc.texinfo.

This file documents the GNU C Library.

   This is ‘The GNU C Library Reference Manual’, for version 2.30.

   Copyright © 1993–2019 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being “Free Software Needs Free Documentation” and
“GNU Lesser General Public License”, the Front-Cover texts being “A GNU
Manual”, and with the Back-Cover Texts as in (a) below.  A copy of the
license is included in the section entitled "GNU Free Documentation
License".

   (a) The FSF’s Back-Cover Text is: “You have the freedom to copy and
modify this GNU manual.  Buying copies from the FSF supports it in
developing GNU and promoting software freedom.”
INFO-DIR-SECTION Software libraries
START-INFO-DIR-ENTRY
* Libc: (libc).                 C library.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION GNU C library functions and macros
START-INFO-DIR-ENTRY
* ALTWERASE: (libc)Local Modes.
* ARGP_ERR_UNKNOWN: (libc)Argp Parser Functions.
* ARG_MAX: (libc)General Limits.
* BC_BASE_MAX: (libc)Utility Limits.
* BC_DIM_MAX: (libc)Utility Limits.
* BC_SCALE_MAX: (libc)Utility Limits.
* BC_STRING_MAX: (libc)Utility Limits.
* BRKINT: (libc)Input Modes.
* BUFSIZ: (libc)Controlling Buffering.
* CCTS_OFLOW: (libc)Control Modes.
* CHAR_BIT: (libc)Width of Type.
* CHILD_MAX: (libc)General Limits.
* CIGNORE: (libc)Control Modes.
* CLK_TCK: (libc)Processor Time.
* CLOCAL: (libc)Control Modes.
* CLOCKS_PER_SEC: (libc)CPU Time.
* COLL_WEIGHTS_MAX: (libc)Utility Limits.
* CPU_CLR: (libc)CPU Affinity.
* CPU_ISSET: (libc)CPU Affinity.
* CPU_SET: (libc)CPU Affinity.
* CPU_SETSIZE: (libc)CPU Affinity.
* CPU_ZERO: (libc)CPU Affinity.
* CREAD: (libc)Control Modes.
* CRTS_IFLOW: (libc)Control Modes.
* CS5: (libc)Control Modes.
* CS6: (libc)Control Modes.
* CS7: (libc)Control Modes.
* CS8: (libc)Control Modes.
* CSIZE: (libc)Control Modes.
* CSTOPB: (libc)Control Modes.
* DTTOIF: (libc)Directory Entries.
* E2BIG: (libc)Error Codes.
* EACCES: (libc)Error Codes.
* EADDRINUSE: (libc)Error Codes.
* EADDRNOTAVAIL: (libc)Error Codes.
* EADV: (libc)Error Codes.
* EAFNOSUPPORT: (libc)Error Codes.
* EAGAIN: (libc)Error Codes.
* EALREADY: (libc)Error Codes.
* EAUTH: (libc)Error Codes.
* EBACKGROUND: (libc)Error Codes.
* EBADE: (libc)Error Codes.
* EBADF: (libc)Error Codes.
* EBADFD: (libc)Error Codes.
* EBADMSG: (libc)Error Codes.
* EBADR: (libc)Error Codes.
* EBADRPC: (libc)Error Codes.
* EBADRQC: (libc)Error Codes.
* EBADSLT: (libc)Error Codes.
* EBFONT: (libc)Error Codes.
* EBUSY: (libc)Error Codes.
* ECANCELED: (libc)Error Codes.
* ECHILD: (libc)Error Codes.
* ECHO: (libc)Local Modes.
* ECHOCTL: (libc)Local Modes.
* ECHOE: (libc)Local Modes.
* ECHOK: (libc)Local Modes.
* ECHOKE: (libc)Local Modes.
* ECHONL: (libc)Local Modes.
* ECHOPRT: (libc)Local Modes.
* ECHRNG: (libc)Error Codes.
* ECOMM: (libc)Error Codes.
* ECONNABORTED: (libc)Error Codes.
* ECONNREFUSED: (libc)Error Codes.
* ECONNRESET: (libc)Error Codes.
* ED: (libc)Error Codes.
* EDEADLK: (libc)Error Codes.
* EDEADLOCK: (libc)Error Codes.
* EDESTADDRREQ: (libc)Error Codes.
* EDIED: (libc)Error Codes.
* EDOM: (libc)Error Codes.
* EDOTDOT: (libc)Error Codes.
* EDQUOT: (libc)Error Codes.
* EEXIST: (libc)Error Codes.
* EFAULT: (libc)Error Codes.
* EFBIG: (libc)Error Codes.
* EFTYPE: (libc)Error Codes.
* EGRATUITOUS: (libc)Error Codes.
* EGREGIOUS: (libc)Error Codes.
* EHOSTDOWN: (libc)Error Codes.
* EHOSTUNREACH: (libc)Error Codes.
* EHWPOISON: (libc)Error Codes.
* EIDRM: (libc)Error Codes.
* EIEIO: (libc)Error Codes.
* EILSEQ: (libc)Error Codes.
* EINPROGRESS: (libc)Error Codes.
* EINTR: (libc)Error Codes.
* EINVAL: (libc)Error Codes.
* EIO: (libc)Error Codes.
* EISCONN: (libc)Error Codes.
* EISDIR: (libc)Error Codes.
* EISNAM: (libc)Error Codes.
* EKEYEXPIRED: (libc)Error Codes.
* EKEYREJECTED: (libc)Error Codes.
* EKEYREVOKED: (libc)Error Codes.
* EL2HLT: (libc)Error Codes.
* EL2NSYNC: (libc)Error Codes.
* EL3HLT: (libc)Error Codes.
* EL3RST: (libc)Error Codes.
* ELIBACC: (libc)Error Codes.
* ELIBBAD: (libc)Error Codes.
* ELIBEXEC: (libc)Error Codes.
* ELIBMAX: (libc)Error Codes.
* ELIBSCN: (libc)Error Codes.
* ELNRNG: (libc)Error Codes.
* ELOOP: (libc)Error Codes.
* EMEDIUMTYPE: (libc)Error Codes.
* EMFILE: (libc)Error Codes.
* EMLINK: (libc)Error Codes.
* EMSGSIZE: (libc)Error Codes.
* EMULTIHOP: (libc)Error Codes.
* ENAMETOOLONG: (libc)Error Codes.
* ENAVAIL: (libc)Error Codes.
* ENEEDAUTH: (libc)Error Codes.
* ENETDOWN: (libc)Error Codes.
* ENETRESET: (libc)Error Codes.
* ENETUNREACH: (libc)Error Codes.
* ENFILE: (libc)Error Codes.
* ENOANO: (libc)Error Codes.
* ENOBUFS: (libc)Error Codes.
* ENOCSI: (libc)Error Codes.
* ENODATA: (libc)Error Codes.
* ENODEV: (libc)Error Codes.
* ENOENT: (libc)Error Codes.
* ENOEXEC: (libc)Error Codes.
* ENOKEY: (libc)Error Codes.
* ENOLCK: (libc)Error Codes.
* ENOLINK: (libc)Error Codes.
* ENOMEDIUM: (libc)Error Codes.
* ENOMEM: (libc)Error Codes.
* ENOMSG: (libc)Error Codes.
* ENONET: (libc)Error Codes.
* ENOPKG: (libc)Error Codes.
* ENOPROTOOPT: (libc)Error Codes.
* ENOSPC: (libc)Error Codes.
* ENOSR: (libc)Error Codes.
* ENOSTR: (libc)Error Codes.
* ENOSYS: (libc)Error Codes.
* ENOTBLK: (libc)Error Codes.
* ENOTCONN: (libc)Error Codes.
* ENOTDIR: (libc)Error Codes.
* ENOTEMPTY: (libc)Error Codes.
* ENOTNAM: (libc)Error Codes.
* ENOTRECOVERABLE: (libc)Error Codes.
* ENOTSOCK: (libc)Error Codes.
* ENOTSUP: (libc)Error Codes.
* ENOTTY: (libc)Error Codes.
* ENOTUNIQ: (libc)Error Codes.
* ENXIO: (libc)Error Codes.
* EOF: (libc)EOF and Errors.
* EOPNOTSUPP: (libc)Error Codes.
* EOVERFLOW: (libc)Error Codes.
* EOWNERDEAD: (libc)Error Codes.
* EPERM: (libc)Error Codes.
* EPFNOSUPPORT: (libc)Error Codes.
* EPIPE: (libc)Error Codes.
* EPROCLIM: (libc)Error Codes.
* EPROCUNAVAIL: (libc)Error Codes.
* EPROGMISMATCH: (libc)Error Codes.
* EPROGUNAVAIL: (libc)Error Codes.
* EPROTO: (libc)Error Codes.
* EPROTONOSUPPORT: (libc)Error Codes.
* EPROTOTYPE: (libc)Error Codes.
* EQUIV_CLASS_MAX: (libc)Utility Limits.
* ERANGE: (libc)Error Codes.
* EREMCHG: (libc)Error Codes.
* EREMOTE: (libc)Error Codes.
* EREMOTEIO: (libc)Error Codes.
* ERESTART: (libc)Error Codes.
* ERFKILL: (libc)Error Codes.
* EROFS: (libc)Error Codes.
* ERPCMISMATCH: (libc)Error Codes.
* ESHUTDOWN: (libc)Error Codes.
* ESOCKTNOSUPPORT: (libc)Error Codes.
* ESPIPE: (libc)Error Codes.
* ESRCH: (libc)Error Codes.
* ESRMNT: (libc)Error Codes.
* ESTALE: (libc)Error Codes.
* ESTRPIPE: (libc)Error Codes.
* ETIME: (libc)Error Codes.
* ETIMEDOUT: (libc)Error Codes.
* ETOOMANYREFS: (libc)Error Codes.
* ETXTBSY: (libc)Error Codes.
* EUCLEAN: (libc)Error Codes.
* EUNATCH: (libc)Error Codes.
* EUSERS: (libc)Error Codes.
* EWOULDBLOCK: (libc)Error Codes.
* EXDEV: (libc)Error Codes.
* EXFULL: (libc)Error Codes.
* EXIT_FAILURE: (libc)Exit Status.
* EXIT_SUCCESS: (libc)Exit Status.
* EXPR_NEST_MAX: (libc)Utility Limits.
* FD_CLOEXEC: (libc)Descriptor Flags.
* FD_CLR: (libc)Waiting for I/O.
* FD_ISSET: (libc)Waiting for I/O.
* FD_SET: (libc)Waiting for I/O.
* FD_SETSIZE: (libc)Waiting for I/O.
* FD_ZERO: (libc)Waiting for I/O.
* FE_SNANS_ALWAYS_SIGNAL: (libc)Infinity and NaN.
* FILENAME_MAX: (libc)Limits for Files.
* FLUSHO: (libc)Local Modes.
* FOPEN_MAX: (libc)Opening Streams.
* FP_ILOGB0: (libc)Exponents and Logarithms.
* FP_ILOGBNAN: (libc)Exponents and Logarithms.
* FP_LLOGB0: (libc)Exponents and Logarithms.
* FP_LLOGBNAN: (libc)Exponents and Logarithms.
* F_DUPFD: (libc)Duplicating Descriptors.
* F_GETFD: (libc)Descriptor Flags.
* F_GETFL: (libc)Getting File Status Flags.
* F_GETLK: (libc)File Locks.
* F_GETOWN: (libc)Interrupt Input.
* F_OFD_GETLK: (libc)Open File Description Locks.
* F_OFD_SETLK: (libc)Open File Description Locks.
* F_OFD_SETLKW: (libc)Open File Description Locks.
* F_OK: (libc)Testing File Access.
* F_SETFD: (libc)Descriptor Flags.
* F_SETFL: (libc)Getting File Status Flags.
* F_SETLK: (libc)File Locks.
* F_SETLKW: (libc)File Locks.
* F_SETOWN: (libc)Interrupt Input.
* HUGE_VAL: (libc)Math Error Reporting.
* HUGE_VALF: (libc)Math Error Reporting.
* HUGE_VALL: (libc)Math Error Reporting.
* HUGE_VAL_FN: (libc)Math Error Reporting.
* HUGE_VAL_FNx: (libc)Math Error Reporting.
* HUPCL: (libc)Control Modes.
* I: (libc)Complex Numbers.
* ICANON: (libc)Local Modes.
* ICRNL: (libc)Input Modes.
* IEXTEN: (libc)Local Modes.
* IFNAMSIZ: (libc)Interface Naming.
* IFTODT: (libc)Directory Entries.
* IGNBRK: (libc)Input Modes.
* IGNCR: (libc)Input Modes.
* IGNPAR: (libc)Input Modes.
* IMAXBEL: (libc)Input Modes.
* INADDR_ANY: (libc)Host Address Data Type.
* INADDR_BROADCAST: (libc)Host Address Data Type.
* INADDR_LOOPBACK: (libc)Host Address Data Type.
* INADDR_NONE: (libc)Host Address Data Type.
* INFINITY: (libc)Infinity and NaN.
* INLCR: (libc)Input Modes.
* INPCK: (libc)Input Modes.
* IPPORT_RESERVED: (libc)Ports.
* IPPORT_USERRESERVED: (libc)Ports.
* ISIG: (libc)Local Modes.
* ISTRIP: (libc)Input Modes.
* IXANY: (libc)Input Modes.
* IXOFF: (libc)Input Modes.
* IXON: (libc)Input Modes.
* LINE_MAX: (libc)Utility Limits.
* LINK_MAX: (libc)Limits for Files.
* L_ctermid: (libc)Identifying the Terminal.
* L_cuserid: (libc)Who Logged In.
* L_tmpnam: (libc)Temporary Files.
* MAXNAMLEN: (libc)Limits for Files.
* MAXSYMLINKS: (libc)Symbolic Links.
* MAX_CANON: (libc)Limits for Files.
* MAX_INPUT: (libc)Limits for Files.
* MB_CUR_MAX: (libc)Selecting the Conversion.
* MB_LEN_MAX: (libc)Selecting the Conversion.
* MDMBUF: (libc)Control Modes.
* MSG_DONTROUTE: (libc)Socket Data Options.
* MSG_OOB: (libc)Socket Data Options.
* MSG_PEEK: (libc)Socket Data Options.
* NAME_MAX: (libc)Limits for Files.
* NAN: (libc)Infinity and NaN.
* NCCS: (libc)Mode Data Types.
* NGROUPS_MAX: (libc)General Limits.
* NOFLSH: (libc)Local Modes.
* NOKERNINFO: (libc)Local Modes.
* NSIG: (libc)Standard Signals.
* NULL: (libc)Null Pointer Constant.
* ONLCR: (libc)Output Modes.
* ONOEOT: (libc)Output Modes.
* OPEN_MAX: (libc)General Limits.
* OPOST: (libc)Output Modes.
* OXTABS: (libc)Output Modes.
* O_ACCMODE: (libc)Access Modes.
* O_APPEND: (libc)Operating Modes.
* O_ASYNC: (libc)Operating Modes.
* O_CREAT: (libc)Open-time Flags.
* O_DIRECTORY: (libc)Open-time Flags.
* O_EXCL: (libc)Open-time Flags.
* O_EXEC: (libc)Access Modes.
* O_EXLOCK: (libc)Open-time Flags.
* O_FSYNC: (libc)Operating Modes.
* O_IGNORE_CTTY: (libc)Open-time Flags.
* O_NDELAY: (libc)Operating Modes.
* O_NOATIME: (libc)Operating Modes.
* O_NOCTTY: (libc)Open-time Flags.
* O_NOLINK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Operating Modes.
* O_NOTRANS: (libc)Open-time Flags.
* O_RDONLY: (libc)Access Modes.
* O_RDWR: (libc)Access Modes.
* O_READ: (libc)Access Modes.
* O_SHLOCK: (libc)Open-time Flags.
* O_SYNC: (libc)Operating Modes.
* O_TMPFILE: (libc)Open-time Flags.
* O_TRUNC: (libc)Open-time Flags.
* O_WRITE: (libc)Access Modes.
* O_WRONLY: (libc)Access Modes.
* PARENB: (libc)Control Modes.
* PARMRK: (libc)Input Modes.
* PARODD: (libc)Control Modes.
* PATH_MAX: (libc)Limits for Files.
* PA_FLAG_MASK: (libc)Parsing a Template String.
* PENDIN: (libc)Local Modes.
* PF_FILE: (libc)Local Namespace Details.
* PF_INET6: (libc)Internet Namespace.
* PF_INET: (libc)Internet Namespace.
* PF_LOCAL: (libc)Local Namespace Details.
* PF_UNIX: (libc)Local Namespace Details.
* PIPE_BUF: (libc)Limits for Files.
* P_tmpdir: (libc)Temporary Files.
* RAND_MAX: (libc)ISO Random.
* RE_DUP_MAX: (libc)General Limits.
* RLIM_INFINITY: (libc)Limits on Resources.
* R_OK: (libc)Testing File Access.
* SA_NOCLDSTOP: (libc)Flags for Sigaction.
* SA_ONSTACK: (libc)Flags for Sigaction.
* SA_RESTART: (libc)Flags for Sigaction.
* SEEK_CUR: (libc)File Positioning.
* SEEK_END: (libc)File Positioning.
* SEEK_SET: (libc)File Positioning.
* SIGABRT: (libc)Program Error Signals.
* SIGALRM: (libc)Alarm Signals.
* SIGBUS: (libc)Program Error Signals.
* SIGCHLD: (libc)Job Control Signals.
* SIGCLD: (libc)Job Control Signals.
* SIGCONT: (libc)Job Control Signals.
* SIGEMT: (libc)Program Error Signals.
* SIGFPE: (libc)Program Error Signals.
* SIGHUP: (libc)Termination Signals.
* SIGILL: (libc)Program Error Signals.
* SIGINFO: (libc)Miscellaneous Signals.
* SIGINT: (libc)Termination Signals.
* SIGIO: (libc)Asynchronous I/O Signals.
* SIGIOT: (libc)Program Error Signals.
* SIGKILL: (libc)Termination Signals.
* SIGLOST: (libc)Operation Error Signals.
* SIGPIPE: (libc)Operation Error Signals.
* SIGPOLL: (libc)Asynchronous I/O Signals.
* SIGPROF: (libc)Alarm Signals.
* SIGQUIT: (libc)Termination Signals.
* SIGSEGV: (libc)Program Error Signals.
* SIGSTOP: (libc)Job Control Signals.
* SIGSYS: (libc)Program Error Signals.
* SIGTERM: (libc)Termination Signals.
* SIGTRAP: (libc)Program Error Signals.
* SIGTSTP: (libc)Job Control Signals.
* SIGTTIN: (libc)Job Control Signals.
* SIGTTOU: (libc)Job Control Signals.
* SIGURG: (libc)Asynchronous I/O Signals.
* SIGUSR1: (libc)Miscellaneous Signals.
* SIGUSR2: (libc)Miscellaneous Signals.
* SIGVTALRM: (libc)Alarm Signals.
* SIGWINCH: (libc)Miscellaneous Signals.
* SIGXCPU: (libc)Operation Error Signals.
* SIGXFSZ: (libc)Operation Error Signals.
* SIG_ERR: (libc)Basic Signal Handling.
* SNAN: (libc)Infinity and NaN.
* SNANF: (libc)Infinity and NaN.
* SNANFN: (libc)Infinity and NaN.
* SNANFNx: (libc)Infinity and NaN.
* SNANL: (libc)Infinity and NaN.
* SOCK_DGRAM: (libc)Communication Styles.
* SOCK_RAW: (libc)Communication Styles.
* SOCK_RDM: (libc)Communication Styles.
* SOCK_SEQPACKET: (libc)Communication Styles.
* SOCK_STREAM: (libc)Communication Styles.
* SOL_SOCKET: (libc)Socket-Level Options.
* SSIZE_MAX: (libc)General Limits.
* STREAM_MAX: (libc)General Limits.
* SUN_LEN: (libc)Local Namespace Details.
* S_IFMT: (libc)Testing File Type.
* S_ISBLK: (libc)Testing File Type.
* S_ISCHR: (libc)Testing File Type.
* S_ISDIR: (libc)Testing File Type.
* S_ISFIFO: (libc)Testing File Type.
* S_ISLNK: (libc)Testing File Type.
* S_ISREG: (libc)Testing File Type.
* S_ISSOCK: (libc)Testing File Type.
* S_TYPEISMQ: (libc)Testing File Type.
* S_TYPEISSEM: (libc)Testing File Type.
* S_TYPEISSHM: (libc)Testing File Type.
* TMP_MAX: (libc)Temporary Files.
* TOSTOP: (libc)Local Modes.
* TZNAME_MAX: (libc)General Limits.
* VDISCARD: (libc)Other Special.
* VDSUSP: (libc)Signal Characters.
* VEOF: (libc)Editing Characters.
* VEOL2: (libc)Editing Characters.
* VEOL: (libc)Editing Characters.
* VERASE: (libc)Editing Characters.
* VINTR: (libc)Signal Characters.
* VKILL: (libc)Editing Characters.
* VLNEXT: (libc)Other Special.
* VMIN: (libc)Noncanonical Input.
* VQUIT: (libc)Signal Characters.
* VREPRINT: (libc)Editing Characters.
* VSTART: (libc)Start/Stop Characters.
* VSTATUS: (libc)Other Special.
* VSTOP: (libc)Start/Stop Characters.
* VSUSP: (libc)Signal Characters.
* VTIME: (libc)Noncanonical Input.
* VWERASE: (libc)Editing Characters.
* WCHAR_MAX: (libc)Extended Char Intro.
* WCHAR_MIN: (libc)Extended Char Intro.
* WCOREDUMP: (libc)Process Completion Status.
* WEOF: (libc)EOF and Errors.
* WEOF: (libc)Extended Char Intro.
* WEXITSTATUS: (libc)Process Completion Status.
* WIFEXITED: (libc)Process Completion Status.
* WIFSIGNALED: (libc)Process Completion Status.
* WIFSTOPPED: (libc)Process Completion Status.
* WSTOPSIG: (libc)Process Completion Status.
* WTERMSIG: (libc)Process Completion Status.
* W_OK: (libc)Testing File Access.
* X_OK: (libc)Testing File Access.
* _Complex_I: (libc)Complex Numbers.
* _Exit: (libc)Termination Internals.
* _IOFBF: (libc)Controlling Buffering.
* _IOLBF: (libc)Controlling Buffering.
* _IONBF: (libc)Controlling Buffering.
* _Imaginary_I: (libc)Complex Numbers.
* _PATH_UTMP: (libc)Manipulating the Database.
* _PATH_WTMP: (libc)Manipulating the Database.
* _POSIX2_C_DEV: (libc)System Options.
* _POSIX2_C_VERSION: (libc)Version Supported.
* _POSIX2_FORT_DEV: (libc)System Options.
* _POSIX2_FORT_RUN: (libc)System Options.
* _POSIX2_LOCALEDEF: (libc)System Options.
* _POSIX2_SW_DEV: (libc)System Options.
* _POSIX_CHOWN_RESTRICTED: (libc)Options for Files.
* _POSIX_JOB_CONTROL: (libc)System Options.
* _POSIX_NO_TRUNC: (libc)Options for Files.
* _POSIX_SAVED_IDS: (libc)System Options.
* _POSIX_VDISABLE: (libc)Options for Files.
* _POSIX_VERSION: (libc)Version Supported.
* __fbufsize: (libc)Controlling Buffering.
* __flbf: (libc)Controlling Buffering.
* __fpending: (libc)Controlling Buffering.
* __fpurge: (libc)Flushing Buffers.
* __freadable: (libc)Opening Streams.
* __freading: (libc)Opening Streams.
* __fsetlocking: (libc)Streams and Threads.
* __fwritable: (libc)Opening Streams.
* __fwriting: (libc)Opening Streams.
* __gconv_end_fct: (libc)glibc iconv Implementation.
* __gconv_fct: (libc)glibc iconv Implementation.
* __gconv_init_fct: (libc)glibc iconv Implementation.
* __ppc_get_timebase: (libc)PowerPC.
* __ppc_get_timebase_freq: (libc)PowerPC.
* __ppc_mdoio: (libc)PowerPC.
* __ppc_mdoom: (libc)PowerPC.
* __ppc_set_ppr_low: (libc)PowerPC.
* __ppc_set_ppr_med: (libc)PowerPC.
* __ppc_set_ppr_med_high: (libc)PowerPC.
* __ppc_set_ppr_med_low: (libc)PowerPC.
* __ppc_set_ppr_very_low: (libc)PowerPC.
* __ppc_yield: (libc)PowerPC.
* __riscv_flush_icache: (libc)RISC-V.
* __va_copy: (libc)Argument Macros.
* _exit: (libc)Termination Internals.
* _flushlbf: (libc)Flushing Buffers.
* _tolower: (libc)Case Conversion.
* _toupper: (libc)Case Conversion.
* a64l: (libc)Encode Binary Data.
* abort: (libc)Aborting a Program.
* abs: (libc)Absolute Value.
* accept: (libc)Accepting Connections.
* access: (libc)Testing File Access.
* acos: (libc)Inverse Trig Functions.
* acosf: (libc)Inverse Trig Functions.
* acosfN: (libc)Inverse Trig Functions.
* acosfNx: (libc)Inverse Trig Functions.
* acosh: (libc)Hyperbolic Functions.
* acoshf: (libc)Hyperbolic Functions.
* acoshfN: (libc)Hyperbolic Functions.
* acoshfNx: (libc)Hyperbolic Functions.
* acoshl: (libc)Hyperbolic Functions.
* acosl: (libc)Inverse Trig Functions.
* addmntent: (libc)mtab.
* addseverity: (libc)Adding Severity Classes.
* adjtime: (libc)High-Resolution Calendar.
* adjtimex: (libc)High-Resolution Calendar.
* aio_cancel64: (libc)Cancel AIO Operations.
* aio_cancel: (libc)Cancel AIO Operations.
* aio_error64: (libc)Status of AIO Operations.
* aio_error: (libc)Status of AIO Operations.
* aio_fsync64: (libc)Synchronizing AIO Operations.
* aio_fsync: (libc)Synchronizing AIO Operations.
* aio_init: (libc)Configuration of AIO.
* aio_read64: (libc)Asynchronous Reads/Writes.
* aio_read: (libc)Asynchronous Reads/Writes.
* aio_return64: (libc)Status of AIO Operations.
* aio_return: (libc)Status of AIO Operations.
* aio_suspend64: (libc)Synchronizing AIO Operations.
* aio_suspend: (libc)Synchronizing AIO Operations.
* aio_write64: (libc)Asynchronous Reads/Writes.
* aio_write: (libc)Asynchronous Reads/Writes.
* alarm: (libc)Setting an Alarm.
* aligned_alloc: (libc)Aligned Memory Blocks.
* alloca: (libc)Variable Size Automatic.
* alphasort64: (libc)Scanning Directory Content.
* alphasort: (libc)Scanning Directory Content.
* argp_error: (libc)Argp Helper Functions.
* argp_failure: (libc)Argp Helper Functions.
* argp_help: (libc)Argp Help.
* argp_parse: (libc)Argp.
* argp_state_help: (libc)Argp Helper Functions.
* argp_usage: (libc)Argp Helper Functions.
* argz_add: (libc)Argz Functions.
* argz_add_sep: (libc)Argz Functions.
* argz_append: (libc)Argz Functions.
* argz_count: (libc)Argz Functions.
* argz_create: (libc)Argz Functions.
* argz_create_sep: (libc)Argz Functions.
* argz_delete: (libc)Argz Functions.
* argz_extract: (libc)Argz Functions.
* argz_insert: (libc)Argz Functions.
* argz_next: (libc)Argz Functions.
* argz_replace: (libc)Argz Functions.
* argz_stringify: (libc)Argz Functions.
* asctime: (libc)Formatting Calendar Time.
* asctime_r: (libc)Formatting Calendar Time.
* asin: (libc)Inverse Trig Functions.
* asinf: (libc)Inverse Trig Functions.
* asinfN: (libc)Inverse Trig Functions.
* asinfNx: (libc)Inverse Trig Functions.
* asinh: (libc)Hyperbolic Functions.
* asinhf: (libc)Hyperbolic Functions.
* asinhfN: (libc)Hyperbolic Functions.
* asinhfNx: (libc)Hyperbolic Functions.
* asinhl: (libc)Hyperbolic Functions.
* asinl: (libc)Inverse Trig Functions.
* asprintf: (libc)Dynamic Output.
* assert: (libc)Consistency Checking.
* assert_perror: (libc)Consistency Checking.
* atan2: (libc)Inverse Trig Functions.
* atan2f: (libc)Inverse Trig Functions.
* atan2fN: (libc)Inverse Trig Functions.
* atan2fNx: (libc)Inverse Trig Functions.
* atan2l: (libc)Inverse Trig Functions.
* atan: (libc)Inverse Trig Functions.
* atanf: (libc)Inverse Trig Functions.
* atanfN: (libc)Inverse Trig Functions.
* atanfNx: (libc)Inverse Trig Functions.
* atanh: (libc)Hyperbolic Functions.
* atanhf: (libc)Hyperbolic Functions.
* atanhfN: (libc)Hyperbolic Functions.
* atanhfNx: (libc)Hyperbolic Functions.
* atanhl: (libc)Hyperbolic Functions.
* atanl: (libc)Inverse Trig Functions.
* atexit: (libc)Cleanups on Exit.
* atof: (libc)Parsing of Floats.
* atoi: (libc)Parsing of Integers.
* atol: (libc)Parsing of Integers.
* atoll: (libc)Parsing of Integers.
* backtrace: (libc)Backtraces.
* backtrace_symbols: (libc)Backtraces.
* backtrace_symbols_fd: (libc)Backtraces.
* basename: (libc)Finding Tokens in a String.
* basename: (libc)Finding Tokens in a String.
* bcmp: (libc)String/Array Comparison.
* bcopy: (libc)Copying Strings and Arrays.
* bind: (libc)Setting Address.
* bind_textdomain_codeset: (libc)Charset conversion in gettext.
* bindtextdomain: (libc)Locating gettext catalog.
* brk: (libc)Resizing the Data Segment.
* bsearch: (libc)Array Search Function.
* btowc: (libc)Converting a Character.
* bzero: (libc)Copying Strings and Arrays.
* cabs: (libc)Absolute Value.
* cabsf: (libc)Absolute Value.
* cabsfN: (libc)Absolute Value.
* cabsfNx: (libc)Absolute Value.
* cabsl: (libc)Absolute Value.
* cacos: (libc)Inverse Trig Functions.
* cacosf: (libc)Inverse Trig Functions.
* cacosfN: (libc)Inverse Trig Functions.
* cacosfNx: (libc)Inverse Trig Functions.
* cacosh: (libc)Hyperbolic Functions.
* cacoshf: (libc)Hyperbolic Functions.
* cacoshfN: (libc)Hyperbolic Functions.
* cacoshfNx: (libc)Hyperbolic Functions.
* cacoshl: (libc)Hyperbolic Functions.
* cacosl: (libc)Inverse Trig Functions.
* call_once: (libc)Call Once.
* calloc: (libc)Allocating Cleared Space.
* canonicalize: (libc)FP Bit Twiddling.
* canonicalize_file_name: (libc)Symbolic Links.
* canonicalizef: (libc)FP Bit Twiddling.
* canonicalizefN: (libc)FP Bit Twiddling.
* canonicalizefNx: (libc)FP Bit Twiddling.
* canonicalizel: (libc)FP Bit Twiddling.
* carg: (libc)Operations on Complex.
* cargf: (libc)Operations on Complex.
* cargfN: (libc)Operations on Complex.
* cargfNx: (libc)Operations on Complex.
* cargl: (libc)Operations on Complex.
* casin: (libc)Inverse Trig Functions.
* casinf: (libc)Inverse Trig Functions.
* casinfN: (libc)Inverse Trig Functions.
* casinfNx: (libc)Inverse Trig Functions.
* casinh: (libc)Hyperbolic Functions.
* casinhf: (libc)Hyperbolic Functions.
* casinhfN: (libc)Hyperbolic Functions.
* casinhfNx: (libc)Hyperbolic Functions.
* casinhl: (libc)Hyperbolic Functions.
* casinl: (libc)Inverse Trig Functions.
* catan: (libc)Inverse Trig Functions.
* catanf: (libc)Inverse Trig Functions.
* catanfN: (libc)Inverse Trig Functions.
* catanfNx: (libc)Inverse Trig Functions.
* catanh: (libc)Hyperbolic Functions.
* catanhf: (libc)Hyperbolic Functions.
* catanhfN: (libc)Hyperbolic Functions.
* catanhfNx: (libc)Hyperbolic Functions.
* catanhl: (libc)Hyperbolic Functions.
* catanl: (libc)Inverse Trig Functions.
* catclose: (libc)The catgets Functions.
* catgets: (libc)The catgets Functions.
* catopen: (libc)The catgets Functions.
* cbrt: (libc)Exponents and Logarithms.
* cbrtf: (libc)Exponents and Logarithms.
* cbrtfN: (libc)Exponents and Logarithms.
* cbrtfNx: (libc)Exponents and Logarithms.
* cbrtl: (libc)Exponents and Logarithms.
* ccos: (libc)Trig Functions.
* ccosf: (libc)Trig Functions.
* ccosfN: (libc)Trig Functions.
* ccosfNx: (libc)Trig Functions.
* ccosh: (libc)Hyperbolic Functions.
* ccoshf: (libc)Hyperbolic Functions.
* ccoshfN: (libc)Hyperbolic Functions.
* ccoshfNx: (libc)Hyperbolic Functions.
* ccoshl: (libc)Hyperbolic Functions.
* ccosl: (libc)Trig Functions.
* ceil: (libc)Rounding Functions.
* ceilf: (libc)Rounding Functions.
* ceilfN: (libc)Rounding Functions.
* ceilfNx: (libc)Rounding Functions.
* ceill: (libc)Rounding Functions.
* cexp: (libc)Exponents and Logarithms.
* cexpf: (libc)Exponents and Logarithms.
* cexpfN: (libc)Exponents and Logarithms.
* cexpfNx: (libc)Exponents and Logarithms.
* cexpl: (libc)Exponents and Logarithms.
* cfgetispeed: (libc)Line Speed.
* cfgetospeed: (libc)Line Speed.
* cfmakeraw: (libc)Noncanonical Input.
* cfsetispeed: (libc)Line Speed.
* cfsetospeed: (libc)Line Speed.
* cfsetspeed: (libc)Line Speed.
* chdir: (libc)Working Directory.
* chmod: (libc)Setting Permissions.
* chown: (libc)File Owner.
* cimag: (libc)Operations on Complex.
* cimagf: (libc)Operations on Complex.
* cimagfN: (libc)Operations on Complex.
* cimagfNx: (libc)Operations on Complex.
* cimagl: (libc)Operations on Complex.
* clearenv: (libc)Environment Access.
* clearerr: (libc)Error Recovery.
* clearerr_unlocked: (libc)Error Recovery.
* clock: (libc)CPU Time.
* clog10: (libc)Exponents and Logarithms.
* clog10f: (libc)Exponents and Logarithms.
* clog10fN: (libc)Exponents and Logarithms.
* clog10fNx: (libc)Exponents and Logarithms.
* clog10l: (libc)Exponents and Logarithms.
* clog: (libc)Exponents and Logarithms.
* clogf: (libc)Exponents and Logarithms.
* clogfN: (libc)Exponents and Logarithms.
* clogfNx: (libc)Exponents and Logarithms.
* clogl: (libc)Exponents and Logarithms.
* close: (libc)Opening and Closing Files.
* closedir: (libc)Reading/Closing Directory.
* closelog: (libc)closelog.
* cnd_broadcast: (libc)ISO C Condition Variables.
* cnd_destroy: (libc)ISO C Condition Variables.
* cnd_init: (libc)ISO C Condition Variables.
* cnd_signal: (libc)ISO C Condition Variables.
* cnd_timedwait: (libc)ISO C Condition Variables.
* cnd_wait: (libc)ISO C Condition Variables.
* confstr: (libc)String Parameters.
* conj: (libc)Operations on Complex.
* conjf: (libc)Operations on Complex.
* conjfN: (libc)Operations on Complex.
* conjfNx: (libc)Operations on Complex.
* conjl: (libc)Operations on Complex.
* connect: (libc)Connecting.
* copy_file_range: (libc)Copying File Data.
* copysign: (libc)FP Bit Twiddling.
* copysignf: (libc)FP Bit Twiddling.
* copysignfN: (libc)FP Bit Twiddling.
* copysignfNx: (libc)FP Bit Twiddling.
* copysignl: (libc)FP Bit Twiddling.
* cos: (libc)Trig Functions.
* cosf: (libc)Trig Functions.
* cosfN: (libc)Trig Functions.
* cosfNx: (libc)Trig Functions.
* cosh: (libc)Hyperbolic Functions.
* coshf: (libc)Hyperbolic Functions.
* coshfN: (libc)Hyperbolic Functions.
* coshfNx: (libc)Hyperbolic Functions.
* coshl: (libc)Hyperbolic Functions.
* cosl: (libc)Trig Functions.
* cpow: (libc)Exponents and Logarithms.
* cpowf: (libc)Exponents and Logarithms.
* cpowfN: (libc)Exponents and Logarithms.
* cpowfNx: (libc)Exponents and Logarithms.
* cpowl: (libc)Exponents and Logarithms.
* cproj: (libc)Operations on Complex.
* cprojf: (libc)Operations on Complex.
* cprojfN: (libc)Operations on Complex.
* cprojfNx: (libc)Operations on Complex.
* cprojl: (libc)Operations on Complex.
* creal: (libc)Operations on Complex.
* crealf: (libc)Operations on Complex.
* crealfN: (libc)Operations on Complex.
* crealfNx: (libc)Operations on Complex.
* creall: (libc)Operations on Complex.
* creat64: (libc)Opening and Closing Files.
* creat: (libc)Opening and Closing Files.
* crypt: (libc)Passphrase Storage.
* crypt_r: (libc)Passphrase Storage.
* csin: (libc)Trig Functions.
* csinf: (libc)Trig Functions.
* csinfN: (libc)Trig Functions.
* csinfNx: (libc)Trig Functions.
* csinh: (libc)Hyperbolic Functions.
* csinhf: (libc)Hyperbolic Functions.
* csinhfN: (libc)Hyperbolic Functions.
* csinhfNx: (libc)Hyperbolic Functions.
* csinhl: (libc)Hyperbolic Functions.
* csinl: (libc)Trig Functions.
* csqrt: (libc)Exponents and Logarithms.
* csqrtf: (libc)Exponents and Logarithms.
* csqrtfN: (libc)Exponents and Logarithms.
* csqrtfNx: (libc)Exponents and Logarithms.
* csqrtl: (libc)Exponents and Logarithms.
* ctan: (libc)Trig Functions.
* ctanf: (libc)Trig Functions.
* ctanfN: (libc)Trig Functions.
* ctanfNx: (libc)Trig Functions.
* ctanh: (libc)Hyperbolic Functions.
* ctanhf: (libc)Hyperbolic Functions.
* ctanhfN: (libc)Hyperbolic Functions.
* ctanhfNx: (libc)Hyperbolic Functions.
* ctanhl: (libc)Hyperbolic Functions.
* ctanl: (libc)Trig Functions.
* ctermid: (libc)Identifying the Terminal.
* ctime: (libc)Formatting Calendar Time.
* ctime_r: (libc)Formatting Calendar Time.
* cuserid: (libc)Who Logged In.
* daddl: (libc)Misc FP Arithmetic.
* dcgettext: (libc)Translation with gettext.
* dcngettext: (libc)Advanced gettext functions.
* ddivl: (libc)Misc FP Arithmetic.
* dgettext: (libc)Translation with gettext.
* difftime: (libc)Elapsed Time.
* dirfd: (libc)Opening a Directory.
* dirname: (libc)Finding Tokens in a String.
* div: (libc)Integer Division.
* dmull: (libc)Misc FP Arithmetic.
* dngettext: (libc)Advanced gettext functions.
* drand48: (libc)SVID Random.
* drand48_r: (libc)SVID Random.
* drem: (libc)Remainder Functions.
* dremf: (libc)Remainder Functions.
* dreml: (libc)Remainder Functions.
* dsubl: (libc)Misc FP Arithmetic.
* dup2: (libc)Duplicating Descriptors.
* dup: (libc)Duplicating Descriptors.
* ecvt: (libc)System V Number Conversion.
* ecvt_r: (libc)System V Number Conversion.
* endfsent: (libc)fstab.
* endgrent: (libc)Scanning All Groups.
* endhostent: (libc)Host Names.
* endmntent: (libc)mtab.
* endnetent: (libc)Networks Database.
* endnetgrent: (libc)Lookup Netgroup.
* endprotoent: (libc)Protocols Database.
* endpwent: (libc)Scanning All Users.
* endservent: (libc)Services Database.
* endutent: (libc)Manipulating the Database.
* endutxent: (libc)XPG Functions.
* envz_add: (libc)Envz Functions.
* envz_entry: (libc)Envz Functions.
* envz_get: (libc)Envz Functions.
* envz_merge: (libc)Envz Functions.
* envz_remove: (libc)Envz Functions.
* envz_strip: (libc)Envz Functions.
* erand48: (libc)SVID Random.
* erand48_r: (libc)SVID Random.
* erf: (libc)Special Functions.
* erfc: (libc)Special Functions.
* erfcf: (libc)Special Functions.
* erfcfN: (libc)Special Functions.
* erfcfNx: (libc)Special Functions.
* erfcl: (libc)Special Functions.
* erff: (libc)Special Functions.
* erffN: (libc)Special Functions.
* erffNx: (libc)Special Functions.
* erfl: (libc)Special Functions.
* err: (libc)Error Messages.
* errno: (libc)Checking for Errors.
* error: (libc)Error Messages.
* error_at_line: (libc)Error Messages.
* errx: (libc)Error Messages.
* execl: (libc)Executing a File.
* execle: (libc)Executing a File.
* execlp: (libc)Executing a File.
* execv: (libc)Executing a File.
* execve: (libc)Executing a File.
* execvp: (libc)Executing a File.
* exit: (libc)Normal Termination.
* exp10: (libc)Exponents and Logarithms.
* exp10f: (libc)Exponents and Logarithms.
* exp10fN: (libc)Exponents and Logarithms.
* exp10fNx: (libc)Exponents and Logarithms.
* exp10l: (libc)Exponents and Logarithms.
* exp2: (libc)Exponents and Logarithms.
* exp2f: (libc)Exponents and Logarithms.
* exp2fN: (libc)Exponents and Logarithms.
* exp2fNx: (libc)Exponents and Logarithms.
* exp2l: (libc)Exponents and Logarithms.
* exp: (libc)Exponents and Logarithms.
* expf: (libc)Exponents and Logarithms.
* expfN: (libc)Exponents and Logarithms.
* expfNx: (libc)Exponents and Logarithms.
* expl: (libc)Exponents and Logarithms.
* explicit_bzero: (libc)Erasing Sensitive Data.
* expm1: (libc)Exponents and Logarithms.
* expm1f: (libc)Exponents and Logarithms.
* expm1fN: (libc)Exponents and Logarithms.
* expm1fNx: (libc)Exponents and Logarithms.
* expm1l: (libc)Exponents and Logarithms.
* fMaddfN: (libc)Misc FP Arithmetic.
* fMaddfNx: (libc)Misc FP Arithmetic.
* fMdivfN: (libc)Misc FP Arithmetic.
* fMdivfNx: (libc)Misc FP Arithmetic.
* fMmulfN: (libc)Misc FP Arithmetic.
* fMmulfNx: (libc)Misc FP Arithmetic.
* fMsubfN: (libc)Misc FP Arithmetic.
* fMsubfNx: (libc)Misc FP Arithmetic.
* fMxaddfN: (libc)Misc FP Arithmetic.
* fMxaddfNx: (libc)Misc FP Arithmetic.
* fMxdivfN: (libc)Misc FP Arithmetic.
* fMxdivfNx: (libc)Misc FP Arithmetic.
* fMxmulfN: (libc)Misc FP Arithmetic.
* fMxmulfNx: (libc)Misc FP Arithmetic.
* fMxsubfN: (libc)Misc FP Arithmetic.
* fMxsubfNx: (libc)Misc FP Arithmetic.
* fabs: (libc)Absolute Value.
* fabsf: (libc)Absolute Value.
* fabsfN: (libc)Absolute Value.
* fabsfNx: (libc)Absolute Value.
* fabsl: (libc)Absolute Value.
* fadd: (libc)Misc FP Arithmetic.
* faddl: (libc)Misc FP Arithmetic.
* fchdir: (libc)Working Directory.
* fchmod: (libc)Setting Permissions.
* fchown: (libc)File Owner.
* fclose: (libc)Closing Streams.
* fcloseall: (libc)Closing Streams.
* fcntl: (libc)Control Operations.
* fcvt: (libc)System V Number Conversion.
* fcvt_r: (libc)System V Number Conversion.
* fdatasync: (libc)Synchronizing I/O.
* fdim: (libc)Misc FP Arithmetic.
* fdimf: (libc)Misc FP Arithmetic.
* fdimfN: (libc)Misc FP Arithmetic.
* fdimfNx: (libc)Misc FP Arithmetic.
* fdiml: (libc)Misc FP Arithmetic.
* fdiv: (libc)Misc FP Arithmetic.
* fdivl: (libc)Misc FP Arithmetic.
* fdopen: (libc)Descriptors and Streams.
* fdopendir: (libc)Opening a Directory.
* feclearexcept: (libc)Status bit operations.
* fedisableexcept: (libc)Control Functions.
* feenableexcept: (libc)Control Functions.
* fegetenv: (libc)Control Functions.
* fegetexcept: (libc)Control Functions.
* fegetexceptflag: (libc)Status bit operations.
* fegetmode: (libc)Control Functions.
* fegetround: (libc)Rounding.
* feholdexcept: (libc)Control Functions.
* feof: (libc)EOF and Errors.
* feof_unlocked: (libc)EOF and Errors.
* feraiseexcept: (libc)Status bit operations.
* ferror: (libc)EOF and Errors.
* ferror_unlocked: (libc)EOF and Errors.
* fesetenv: (libc)Control Functions.
* fesetexcept: (libc)Status bit operations.
* fesetexceptflag: (libc)Status bit operations.
* fesetmode: (libc)Control Functions.
* fesetround: (libc)Rounding.
* fetestexcept: (libc)Status bit operations.
* fetestexceptflag: (libc)Status bit operations.
* feupdateenv: (libc)Control Functions.
* fflush: (libc)Flushing Buffers.
* fflush_unlocked: (libc)Flushing Buffers.
* fgetc: (libc)Character Input.
* fgetc_unlocked: (libc)Character Input.
* fgetgrent: (libc)Scanning All Groups.
* fgetgrent_r: (libc)Scanning All Groups.
* fgetpos64: (libc)Portable Positioning.
* fgetpos: (libc)Portable Positioning.
* fgetpwent: (libc)Scanning All Users.
* fgetpwent_r: (libc)Scanning All Users.
* fgets: (libc)Line Input.
* fgets_unlocked: (libc)Line Input.
* fgetwc: (libc)Character Input.
* fgetwc_unlocked: (libc)Character Input.
* fgetws: (libc)Line Input.
* fgetws_unlocked: (libc)Line Input.
* fileno: (libc)Descriptors and Streams.
* fileno_unlocked: (libc)Descriptors and Streams.
* finite: (libc)Floating Point Classes.
* finitef: (libc)Floating Point Classes.
* finitel: (libc)Floating Point Classes.
* flockfile: (libc)Streams and Threads.
* floor: (libc)Rounding Functions.
* floorf: (libc)Rounding Functions.
* floorfN: (libc)Rounding Functions.
* floorfNx: (libc)Rounding Functions.
* floorl: (libc)Rounding Functions.
* fma: (libc)Misc FP Arithmetic.
* fmaf: (libc)Misc FP Arithmetic.
* fmafN: (libc)Misc FP Arithmetic.
* fmafNx: (libc)Misc FP Arithmetic.
* fmal: (libc)Misc FP Arithmetic.
* fmax: (libc)Misc FP Arithmetic.
* fmaxf: (libc)Misc FP Arithmetic.
* fmaxfN: (libc)Misc FP Arithmetic.
* fmaxfNx: (libc)Misc FP Arithmetic.
* fmaxl: (libc)Misc FP Arithmetic.
* fmaxmag: (libc)Misc FP Arithmetic.
* fmaxmagf: (libc)Misc FP Arithmetic.
* fmaxmagfN: (libc)Misc FP Arithmetic.
* fmaxmagfNx: (libc)Misc FP Arithmetic.
* fmaxmagl: (libc)Misc FP Arithmetic.
* fmemopen: (libc)String Streams.
* fmin: (libc)Misc FP Arithmetic.
* fminf: (libc)Misc FP Arithmetic.
* fminfN: (libc)Misc FP Arithmetic.
* fminfNx: (libc)Misc FP Arithmetic.
* fminl: (libc)Misc FP Arithmetic.
* fminmag: (libc)Misc FP Arithmetic.
* fminmagf: (libc)Misc FP Arithmetic.
* fminmagfN: (libc)Misc FP Arithmetic.
* fminmagfNx: (libc)Misc FP Arithmetic.
* fminmagl: (libc)Misc FP Arithmetic.
* fmod: (libc)Remainder Functions.
* fmodf: (libc)Remainder Functions.
* fmodfN: (libc)Remainder Functions.
* fmodfNx: (libc)Remainder Functions.
* fmodl: (libc)Remainder Functions.
* fmtmsg: (libc)Printing Formatted Messages.
* fmul: (libc)Misc FP Arithmetic.
* fmull: (libc)Misc FP Arithmetic.
* fnmatch: (libc)Wildcard Matching.
* fopen64: (libc)Opening Streams.
* fopen: (libc)Opening Streams.
* fopencookie: (libc)Streams and Cookies.
* fork: (libc)Creating a Process.
* forkpty: (libc)Pseudo-Terminal Pairs.
* fpathconf: (libc)Pathconf.
* fpclassify: (libc)Floating Point Classes.
* fprintf: (libc)Formatted Output Functions.
* fputc: (libc)Simple Output.
* fputc_unlocked: (libc)Simple Output.
* fputs: (libc)Simple Output.
* fputs_unlocked: (libc)Simple Output.
* fputwc: (libc)Simple Output.
* fputwc_unlocked: (libc)Simple Output.
* fputws: (libc)Simple Output.
* fputws_unlocked: (libc)Simple Output.
* fread: (libc)Block Input/Output.
* fread_unlocked: (libc)Block Input/Output.
* free: (libc)Freeing after Malloc.
* freopen64: (libc)Opening Streams.
* freopen: (libc)Opening Streams.
* frexp: (libc)Normalization Functions.
* frexpf: (libc)Normalization Functions.
* frexpfN: (libc)Normalization Functions.
* frexpfNx: (libc)Normalization Functions.
* frexpl: (libc)Normalization Functions.
* fromfp: (libc)Rounding Functions.
* fromfpf: (libc)Rounding Functions.
* fromfpfN: (libc)Rounding Functions.
* fromfpfNx: (libc)Rounding Functions.
* fromfpl: (libc)Rounding Functions.
* fromfpx: (libc)Rounding Functions.
* fromfpxf: (libc)Rounding Functions.
* fromfpxfN: (libc)Rounding Functions.
* fromfpxfNx: (libc)Rounding Functions.
* fromfpxl: (libc)Rounding Functions.
* fscanf: (libc)Formatted Input Functions.
* fseek: (libc)File Positioning.
* fseeko64: (libc)File Positioning.
* fseeko: (libc)File Positioning.
* fsetpos64: (libc)Portable Positioning.
* fsetpos: (libc)Portable Positioning.
* fstat64: (libc)Reading Attributes.
* fstat: (libc)Reading Attributes.
* fsub: (libc)Misc FP Arithmetic.
* fsubl: (libc)Misc FP Arithmetic.
* fsync: (libc)Synchronizing I/O.
* ftell: (libc)File Positioning.
* ftello64: (libc)File Positioning.
* ftello: (libc)File Positioning.
* ftruncate64: (libc)File Size.
* ftruncate: (libc)File Size.
* ftrylockfile: (libc)Streams and Threads.
* ftw64: (libc)Working with Directory Trees.
* ftw: (libc)Working with Directory Trees.
* funlockfile: (libc)Streams and Threads.
* futimes: (libc)File Times.
* fwide: (libc)Streams and I18N.
* fwprintf: (libc)Formatted Output Functions.
* fwrite: (libc)Block Input/Output.
* fwrite_unlocked: (libc)Block Input/Output.
* fwscanf: (libc)Formatted Input Functions.
* gamma: (libc)Special Functions.
* gammaf: (libc)Special Functions.
* gammal: (libc)Special Functions.
* gcvt: (libc)System V Number Conversion.
* get_avphys_pages: (libc)Query Memory Parameters.
* get_current_dir_name: (libc)Working Directory.
* get_nprocs: (libc)Processor Resources.
* get_nprocs_conf: (libc)Processor Resources.
* get_phys_pages: (libc)Query Memory Parameters.
* getauxval: (libc)Auxiliary Vector.
* getc: (libc)Character Input.
* getc_unlocked: (libc)Character Input.
* getchar: (libc)Character Input.
* getchar_unlocked: (libc)Character Input.
* getcontext: (libc)System V contexts.
* getcpu: (libc)CPU Affinity.
* getcwd: (libc)Working Directory.
* getdate: (libc)General Time String Parsing.
* getdate_r: (libc)General Time String Parsing.
* getdelim: (libc)Line Input.
* getdents64: (libc)Low-level Directory Access.
* getdomainnname: (libc)Host Identification.
* getegid: (libc)Reading Persona.
* getentropy: (libc)Unpredictable Bytes.
* getenv: (libc)Environment Access.
* geteuid: (libc)Reading Persona.
* getfsent: (libc)fstab.
* getfsfile: (libc)fstab.
* getfsspec: (libc)fstab.
* getgid: (libc)Reading Persona.
* getgrent: (libc)Scanning All Groups.
* getgrent_r: (libc)Scanning All Groups.
* getgrgid: (libc)Lookup Group.
* getgrgid_r: (libc)Lookup Group.
* getgrnam: (libc)Lookup Group.
* getgrnam_r: (libc)Lookup Group.
* getgrouplist: (libc)Setting Groups.
* getgroups: (libc)Reading Persona.
* gethostbyaddr: (libc)Host Names.
* gethostbyaddr_r: (libc)Host Names.
* gethostbyname2: (libc)Host Names.
* gethostbyname2_r: (libc)Host Names.
* gethostbyname: (libc)Host Names.
* gethostbyname_r: (libc)Host Names.
* gethostent: (libc)Host Names.
* gethostid: (libc)Host Identification.
* gethostname: (libc)Host Identification.
* getitimer: (libc)Setting an Alarm.
* getline: (libc)Line Input.
* getloadavg: (libc)Processor Resources.
* getlogin: (libc)Who Logged In.
* getmntent: (libc)mtab.
* getmntent_r: (libc)mtab.
* getnetbyaddr: (libc)Networks Database.
* getnetbyname: (libc)Networks Database.
* getnetent: (libc)Networks Database.
* getnetgrent: (libc)Lookup Netgroup.
* getnetgrent_r: (libc)Lookup Netgroup.
* getopt: (libc)Using Getopt.
* getopt_long: (libc)Getopt Long Options.
* getopt_long_only: (libc)Getopt Long Options.
* getpagesize: (libc)Query Memory Parameters.
* getpass: (libc)getpass.
* getpayload: (libc)FP Bit Twiddling.
* getpayloadf: (libc)FP Bit Twiddling.
* getpayloadfN: (libc)FP Bit Twiddling.
* getpayloadfNx: (libc)FP Bit Twiddling.
* getpayloadl: (libc)FP Bit Twiddling.
* getpeername: (libc)Who is Connected.
* getpgid: (libc)Process Group Functions.
* getpgrp: (libc)Process Group Functions.
* getpid: (libc)Process Identification.
* getppid: (libc)Process Identification.
* getpriority: (libc)Traditional Scheduling Functions.
* getprotobyname: (libc)Protocols Database.
* getprotobynumber: (libc)Protocols Database.
* getprotoent: (libc)Protocols Database.
* getpt: (libc)Allocation.
* getpwent: (libc)Scanning All Users.
* getpwent_r: (libc)Scanning All Users.
* getpwnam: (libc)Lookup User.
* getpwnam_r: (libc)Lookup User.
* getpwuid: (libc)Lookup User.
* getpwuid_r: (libc)Lookup User.
* getrandom: (libc)Unpredictable Bytes.
* getrlimit64: (libc)Limits on Resources.
* getrlimit: (libc)Limits on Resources.
* getrusage: (libc)Resource Usage.
* gets: (libc)Line Input.
* getservbyname: (libc)Services Database.
* getservbyport: (libc)Services Database.
* getservent: (libc)Services Database.
* getsid: (libc)Process Group Functions.
* getsockname: (libc)Reading Address.
* getsockopt: (libc)Socket Option Functions.
* getsubopt: (libc)Suboptions.
* gettext: (libc)Translation with gettext.
* gettid: (libc)Process Identification.
* gettimeofday: (libc)High-Resolution Calendar.
* getuid: (libc)Reading Persona.
* getumask: (libc)Setting Permissions.
* getutent: (libc)Manipulating the Database.
* getutent_r: (libc)Manipulating the Database.
* getutid: (libc)Manipulating the Database.
* getutid_r: (libc)Manipulating the Database.
* getutline: (libc)Manipulating the Database.
* getutline_r: (libc)Manipulating the Database.
* getutmp: (libc)XPG Functions.
* getutmpx: (libc)XPG Functions.
* getutxent: (libc)XPG Functions.
* getutxid: (libc)XPG Functions.
* getutxline: (libc)XPG Functions.
* getw: (libc)Character Input.
* getwc: (libc)Character Input.
* getwc_unlocked: (libc)Character Input.
* getwchar: (libc)Character Input.
* getwchar_unlocked: (libc)Character Input.
* getwd: (libc)Working Directory.
* glob64: (libc)Calling Glob.
* glob: (libc)Calling Glob.
* globfree64: (libc)More Flags for Globbing.
* globfree: (libc)More Flags for Globbing.
* gmtime: (libc)Broken-down Time.
* gmtime_r: (libc)Broken-down Time.
* grantpt: (libc)Allocation.
* gsignal: (libc)Signaling Yourself.
* gtty: (libc)BSD Terminal Modes.
* hasmntopt: (libc)mtab.
* hcreate: (libc)Hash Search Function.
* hcreate_r: (libc)Hash Search Function.
* hdestroy: (libc)Hash Search Function.
* hdestroy_r: (libc)Hash Search Function.
* hsearch: (libc)Hash Search Function.
* hsearch_r: (libc)Hash Search Function.
* htonl: (libc)Byte Order.
* htons: (libc)Byte Order.
* hypot: (libc)Exponents and Logarithms.
* hypotf: (libc)Exponents and Logarithms.
* hypotfN: (libc)Exponents and Logarithms.
* hypotfNx: (libc)Exponents and Logarithms.
* hypotl: (libc)Exponents and Logarithms.
* iconv: (libc)Generic Conversion Interface.
* iconv_close: (libc)Generic Conversion Interface.
* iconv_open: (libc)Generic Conversion Interface.
* if_freenameindex: (libc)Interface Naming.
* if_indextoname: (libc)Interface Naming.
* if_nameindex: (libc)Interface Naming.
* if_nametoindex: (libc)Interface Naming.
* ilogb: (libc)Exponents and Logarithms.
* ilogbf: (libc)Exponents and Logarithms.
* ilogbfN: (libc)Exponents and Logarithms.
* ilogbfNx: (libc)Exponents and Logarithms.
* ilogbl: (libc)Exponents and Logarithms.
* imaxabs: (libc)Absolute Value.
* imaxdiv: (libc)Integer Division.
* in6addr_any: (libc)Host Address Data Type.
* in6addr_loopback: (libc)Host Address Data Type.
* index: (libc)Search Functions.
* inet_addr: (libc)Host Address Functions.
* inet_aton: (libc)Host Address Functions.
* inet_lnaof: (libc)Host Address Functions.
* inet_makeaddr: (libc)Host Address Functions.
* inet_netof: (libc)Host Address Functions.
* inet_network: (libc)Host Address Functions.
* inet_ntoa: (libc)Host Address Functions.
* inet_ntop: (libc)Host Address Functions.
* inet_pton: (libc)Host Address Functions.
* initgroups: (libc)Setting Groups.
* initstate: (libc)BSD Random.
* initstate_r: (libc)BSD Random.
* innetgr: (libc)Netgroup Membership.
* ioctl: (libc)IOCTLs.
* isalnum: (libc)Classification of Characters.
* isalpha: (libc)Classification of Characters.
* isascii: (libc)Classification of Characters.
* isatty: (libc)Is It a Terminal.
* isblank: (libc)Classification of Characters.
* iscanonical: (libc)Floating Point Classes.
* iscntrl: (libc)Classification of Characters.
* isdigit: (libc)Classification of Characters.
* iseqsig: (libc)FP Comparison Functions.
* isfinite: (libc)Floating Point Classes.
* isgraph: (libc)Classification of Characters.
* isgreater: (libc)FP Comparison Functions.
* isgreaterequal: (libc)FP Comparison Functions.
* isinf: (libc)Floating Point Classes.
* isinff: (libc)Floating Point Classes.
* isinfl: (libc)Floating Point Classes.
* isless: (libc)FP Comparison Functions.
* islessequal: (libc)FP Comparison Functions.
* islessgreater: (libc)FP Comparison Functions.
* islower: (libc)Classification of Characters.
* isnan: (libc)Floating Point Classes.
* isnan: (libc)Floating Point Classes.
* isnanf: (libc)Floating Point Classes.
* isnanl: (libc)Floating Point Classes.
* isnormal: (libc)Floating Point Classes.
* isprint: (libc)Classification of Characters.
* ispunct: (libc)Classification of Characters.
* issignaling: (libc)Floating Point Classes.
* isspace: (libc)Classification of Characters.
* issubnormal: (libc)Floating Point Classes.
* isunordered: (libc)FP Comparison Functions.
* isupper: (libc)Classification of Characters.
* iswalnum: (libc)Classification of Wide Characters.
* iswalpha: (libc)Classification of Wide Characters.
* iswblank: (libc)Classification of Wide Characters.
* iswcntrl: (libc)Classification of Wide Characters.
* iswctype: (libc)Classification of Wide Characters.
* iswdigit: (libc)Classification of Wide Characters.
* iswgraph: (libc)Classification of Wide Characters.
* iswlower: (libc)Classification of Wide Characters.
* iswprint: (libc)Classification of Wide Characters.
* iswpunct: (libc)Classification of Wide Characters.
* iswspace: (libc)Classification of Wide Characters.
* iswupper: (libc)Classification of Wide Characters.
* iswxdigit: (libc)Classification of Wide Characters.
* isxdigit: (libc)Classification of Characters.
* iszero: (libc)Floating Point Classes.
* j0: (libc)Special Functions.
* j0f: (libc)Special Functions.
* j0fN: (libc)Special Functions.
* j0fNx: (libc)Special Functions.
* j0l: (libc)Special Functions.
* j1: (libc)Special Functions.
* j1f: (libc)Special Functions.
* j1fN: (libc)Special Functions.
* j1fNx: (libc)Special Functions.
* j1l: (libc)Special Functions.
* jn: (libc)Special Functions.
* jnf: (libc)Special Functions.
* jnfN: (libc)Special Functions.
* jnfNx: (libc)Special Functions.
* jnl: (libc)Special Functions.
* jrand48: (libc)SVID Random.
* jrand48_r: (libc)SVID Random.
* kill: (libc)Signaling Another Process.
* killpg: (libc)Signaling Another Process.
* l64a: (libc)Encode Binary Data.
* labs: (libc)Absolute Value.
* lcong48: (libc)SVID Random.
* lcong48_r: (libc)SVID Random.
* ldexp: (libc)Normalization Functions.
* ldexpf: (libc)Normalization Functions.
* ldexpfN: (libc)Normalization Functions.
* ldexpfNx: (libc)Normalization Functions.
* ldexpl: (libc)Normalization Functions.
* ldiv: (libc)Integer Division.
* lfind: (libc)Array Search Function.
* lgamma: (libc)Special Functions.
* lgamma_r: (libc)Special Functions.
* lgammaf: (libc)Special Functions.
* lgammafN: (libc)Special Functions.
* lgammafN_r: (libc)Special Functions.
* lgammafNx: (libc)Special Functions.
* lgammafNx_r: (libc)Special Functions.
* lgammaf_r: (libc)Special Functions.
* lgammal: (libc)Special Functions.
* lgammal_r: (libc)Special Functions.
* link: (libc)Hard Links.
* linkat: (libc)Hard Links.
* lio_listio64: (libc)Asynchronous Reads/Writes.
* lio_listio: (libc)Asynchronous Reads/Writes.
* listen: (libc)Listening.
* llabs: (libc)Absolute Value.
* lldiv: (libc)Integer Division.
* llogb: (libc)Exponents and Logarithms.
* llogbf: (libc)Exponents and Logarithms.
* llogbfN: (libc)Exponents and Logarithms.
* llogbfNx: (libc)Exponents and Logarithms.
* llogbl: (libc)Exponents and Logarithms.
* llrint: (libc)Rounding Functions.
* llrintf: (libc)Rounding Functions.
* llrintfN: (libc)Rounding Functions.
* llrintfNx: (libc)Rounding Functions.
* llrintl: (libc)Rounding Functions.
* llround: (libc)Rounding Functions.
* llroundf: (libc)Rounding Functions.
* llroundfN: (libc)Rounding Functions.
* llroundfNx: (libc)Rounding Functions.
* llroundl: (libc)Rounding Functions.
* localeconv: (libc)The Lame Way to Locale Data.
* localtime: (libc)Broken-down Time.
* localtime_r: (libc)Broken-down Time.
* log10: (libc)Exponents and Logarithms.
* log10f: (libc)Exponents and Logarithms.
* log10fN: (libc)Exponents and Logarithms.
* log10fNx: (libc)Exponents and Logarithms.
* log10l: (libc)Exponents and Logarithms.
* log1p: (libc)Exponents and Logarithms.
* log1pf: (libc)Exponents and Logarithms.
* log1pfN: (libc)Exponents and Logarithms.
* log1pfNx: (libc)Exponents and Logarithms.
* log1pl: (libc)Exponents and Logarithms.
* log2: (libc)Exponents and Logarithms.
* log2f: (libc)Exponents and Logarithms.
* log2fN: (libc)Exponents and Logarithms.
* log2fNx: (libc)Exponents and Logarithms.
* log2l: (libc)Exponents and Logarithms.
* log: (libc)Exponents and Logarithms.
* logb: (libc)Exponents and Logarithms.
* logbf: (libc)Exponents and Logarithms.
* logbfN: (libc)Exponents and Logarithms.
* logbfNx: (libc)Exponents and Logarithms.
* logbl: (libc)Exponents and Logarithms.
* logf: (libc)Exponents and Logarithms.
* logfN: (libc)Exponents and Logarithms.
* logfNx: (libc)Exponents and Logarithms.
* login: (libc)Logging In and Out.
* login_tty: (libc)Logging In and Out.
* logl: (libc)Exponents and Logarithms.
* logout: (libc)Logging In and Out.
* logwtmp: (libc)Logging In and Out.
* longjmp: (libc)Non-Local Details.
* lrand48: (libc)SVID Random.
* lrand48_r: (libc)SVID Random.
* lrint: (libc)Rounding Functions.
* lrintf: (libc)Rounding Functions.
* lrintfN: (libc)Rounding Functions.
* lrintfNx: (libc)Rounding Functions.
* lrintl: (libc)Rounding Functions.
* lround: (libc)Rounding Functions.
* lroundf: (libc)Rounding Functions.
* lroundfN: (libc)Rounding Functions.
* lroundfNx: (libc)Rounding Functions.
* lroundl: (libc)Rounding Functions.
* lsearch: (libc)Array Search Function.
* lseek64: (libc)File Position Primitive.
* lseek: (libc)File Position Primitive.
* lstat64: (libc)Reading Attributes.
* lstat: (libc)Reading Attributes.
* lutimes: (libc)File Times.
* madvise: (libc)Memory-mapped I/O.
* makecontext: (libc)System V contexts.
* mallinfo: (libc)Statistics of Malloc.
* malloc: (libc)Basic Allocation.
* mallopt: (libc)Malloc Tunable Parameters.
* mblen: (libc)Non-reentrant Character Conversion.
* mbrlen: (libc)Converting a Character.
* mbrtowc: (libc)Converting a Character.
* mbsinit: (libc)Keeping the state.
* mbsnrtowcs: (libc)Converting Strings.
* mbsrtowcs: (libc)Converting Strings.
* mbstowcs: (libc)Non-reentrant String Conversion.
* mbtowc: (libc)Non-reentrant Character Conversion.
* mcheck: (libc)Heap Consistency Checking.
* memalign: (libc)Aligned Memory Blocks.
* memccpy: (libc)Copying Strings and Arrays.
* memchr: (libc)Search Functions.
* memcmp: (libc)String/Array Comparison.
* memcpy: (libc)Copying Strings and Arrays.
* memfd_create: (libc)Memory-mapped I/O.
* memfrob: (libc)Obfuscating Data.
* memmem: (libc)Search Functions.
* memmove: (libc)Copying Strings and Arrays.
* mempcpy: (libc)Copying Strings and Arrays.
* memrchr: (libc)Search Functions.
* memset: (libc)Copying Strings and Arrays.
* mkdir: (libc)Creating Directories.
* mkdtemp: (libc)Temporary Files.
* mkfifo: (libc)FIFO Special Files.
* mknod: (libc)Making Special Files.
* mkstemp: (libc)Temporary Files.
* mktemp: (libc)Temporary Files.
* mktime: (libc)Broken-down Time.
* mlock2: (libc)Page Lock Functions.
* mlock: (libc)Page Lock Functions.
* mlockall: (libc)Page Lock Functions.
* mmap64: (libc)Memory-mapped I/O.
* mmap: (libc)Memory-mapped I/O.
* modf: (libc)Rounding Functions.
* modff: (libc)Rounding Functions.
* modffN: (libc)Rounding Functions.
* modffNx: (libc)Rounding Functions.
* modfl: (libc)Rounding Functions.
* mount: (libc)Mount-Unmount-Remount.
* mprobe: (libc)Heap Consistency Checking.
* mprotect: (libc)Memory Protection.
* mrand48: (libc)SVID Random.
* mrand48_r: (libc)SVID Random.
* mremap: (libc)Memory-mapped I/O.
* msync: (libc)Memory-mapped I/O.
* mtrace: (libc)Tracing malloc.
* mtx_destroy: (libc)ISO C Mutexes.
* mtx_init: (libc)ISO C Mutexes.
* mtx_lock: (libc)ISO C Mutexes.
* mtx_timedlock: (libc)ISO C Mutexes.
* mtx_trylock: (libc)ISO C Mutexes.
* mtx_unlock: (libc)ISO C Mutexes.
* munlock: (libc)Page Lock Functions.
* munlockall: (libc)Page Lock Functions.
* munmap: (libc)Memory-mapped I/O.
* muntrace: (libc)Tracing malloc.
* nan: (libc)FP Bit Twiddling.
* nanf: (libc)FP Bit Twiddling.
* nanfN: (libc)FP Bit Twiddling.
* nanfNx: (libc)FP Bit Twiddling.
* nanl: (libc)FP Bit Twiddling.
* nanosleep: (libc)Sleeping.
* nearbyint: (libc)Rounding Functions.
* nearbyintf: (libc)Rounding Functions.
* nearbyintfN: (libc)Rounding Functions.
* nearbyintfNx: (libc)Rounding Functions.
* nearbyintl: (libc)Rounding Functions.
* nextafter: (libc)FP Bit Twiddling.
* nextafterf: (libc)FP Bit Twiddling.
* nextafterfN: (libc)FP Bit Twiddling.
* nextafterfNx: (libc)FP Bit Twiddling.
* nextafterl: (libc)FP Bit Twiddling.
* nextdown: (libc)FP Bit Twiddling.
* nextdownf: (libc)FP Bit Twiddling.
* nextdownfN: (libc)FP Bit Twiddling.
* nextdownfNx: (libc)FP Bit Twiddling.
* nextdownl: (libc)FP Bit Twiddling.
* nexttoward: (libc)FP Bit Twiddling.
* nexttowardf: (libc)FP Bit Twiddling.
* nexttowardl: (libc)FP Bit Twiddling.
* nextup: (libc)FP Bit Twiddling.
* nextupf: (libc)FP Bit Twiddling.
* nextupfN: (libc)FP Bit Twiddling.
* nextupfNx: (libc)FP Bit Twiddling.
* nextupl: (libc)FP Bit Twiddling.
* nftw64: (libc)Working with Directory Trees.
* nftw: (libc)Working with Directory Trees.
* ngettext: (libc)Advanced gettext functions.
* nice: (libc)Traditional Scheduling Functions.
* nl_langinfo: (libc)The Elegant and Fast Way.
* nrand48: (libc)SVID Random.
* nrand48_r: (libc)SVID Random.
* ntohl: (libc)Byte Order.
* ntohs: (libc)Byte Order.
* ntp_adjtime: (libc)High Accuracy Clock.
* ntp_gettime: (libc)High Accuracy Clock.
* obstack_1grow: (libc)Growing Objects.
* obstack_1grow_fast: (libc)Extra Fast Growing.
* obstack_alignment_mask: (libc)Obstacks Data Alignment.
* obstack_alloc: (libc)Allocation in an Obstack.
* obstack_base: (libc)Status of an Obstack.
* obstack_blank: (libc)Growing Objects.
* obstack_blank_fast: (libc)Extra Fast Growing.
* obstack_chunk_size: (libc)Obstack Chunks.
* obstack_copy0: (libc)Allocation in an Obstack.
* obstack_copy: (libc)Allocation in an Obstack.
* obstack_finish: (libc)Growing Objects.
* obstack_free: (libc)Freeing Obstack Objects.
* obstack_grow0: (libc)Growing Objects.
* obstack_grow: (libc)Growing Objects.
* obstack_init: (libc)Preparing for Obstacks.
* obstack_int_grow: (libc)Growing Objects.
* obstack_int_grow_fast: (libc)Extra Fast Growing.
* obstack_next_free: (libc)Status of an Obstack.
* obstack_object_size: (libc)Growing Objects.
* obstack_object_size: (libc)Status of an Obstack.
* obstack_printf: (libc)Dynamic Output.
* obstack_ptr_grow: (libc)Growing Objects.
* obstack_ptr_grow_fast: (libc)Extra Fast Growing.
* obstack_room: (libc)Extra Fast Growing.
* obstack_vprintf: (libc)Variable Arguments Output.
* offsetof: (libc)Structure Measurement.
* on_exit: (libc)Cleanups on Exit.
* open64: (libc)Opening and Closing Files.
* open: (libc)Opening and Closing Files.
* open_memstream: (libc)String Streams.
* opendir: (libc)Opening a Directory.
* openlog: (libc)openlog.
* openpty: (libc)Pseudo-Terminal Pairs.
* parse_printf_format: (libc)Parsing a Template String.
* pathconf: (libc)Pathconf.
* pause: (libc)Using Pause.
* pclose: (libc)Pipe to a Subprocess.
* perror: (libc)Error Messages.
* pipe: (libc)Creating a Pipe.
* pkey_alloc: (libc)Memory Protection.
* pkey_free: (libc)Memory Protection.
* pkey_get: (libc)Memory Protection.
* pkey_mprotect: (libc)Memory Protection.
* pkey_set: (libc)Memory Protection.
* popen: (libc)Pipe to a Subprocess.
* posix_fallocate64: (libc)Storage Allocation.
* posix_fallocate: (libc)Storage Allocation.
* posix_memalign: (libc)Aligned Memory Blocks.
* pow: (libc)Exponents and Logarithms.
* powf: (libc)Exponents and Logarithms.
* powfN: (libc)Exponents and Logarithms.
* powfNx: (libc)Exponents and Logarithms.
* powl: (libc)Exponents and Logarithms.
* pread64: (libc)I/O Primitives.
* pread: (libc)I/O Primitives.
* preadv2: (libc)Scatter-Gather.
* preadv64: (libc)Scatter-Gather.
* preadv64v2: (libc)Scatter-Gather.
* preadv: (libc)Scatter-Gather.
* printf: (libc)Formatted Output Functions.
* printf_size: (libc)Predefined Printf Handlers.
* printf_size_info: (libc)Predefined Printf Handlers.
* psignal: (libc)Signal Messages.
* pthread_cond_clockwait: (libc)Default Thread Attributes.
* pthread_getattr_default_np: (libc)Default Thread Attributes.
* pthread_getspecific: (libc)Thread-specific Data.
* pthread_key_create: (libc)Thread-specific Data.
* pthread_key_delete: (libc)Thread-specific Data.
* pthread_rwlock_clockrdlock: (libc)Default Thread Attributes.
* pthread_rwlock_clockwrlock: (libc)Default Thread Attributes.
* pthread_setattr_default_np: (libc)Default Thread Attributes.
* pthread_setspecific: (libc)Thread-specific Data.
* ptsname: (libc)Allocation.
* ptsname_r: (libc)Allocation.
* putc: (libc)Simple Output.
* putc_unlocked: (libc)Simple Output.
* putchar: (libc)Simple Output.
* putchar_unlocked: (libc)Simple Output.
* putenv: (libc)Environment Access.
* putpwent: (libc)Writing a User Entry.
* puts: (libc)Simple Output.
* pututline: (libc)Manipulating the Database.
* pututxline: (libc)XPG Functions.
* putw: (libc)Simple Output.
* putwc: (libc)Simple Output.
* putwc_unlocked: (libc)Simple Output.
* putwchar: (libc)Simple Output.
* putwchar_unlocked: (libc)Simple Output.
* pwrite64: (libc)I/O Primitives.
* pwrite: (libc)I/O Primitives.
* pwritev2: (libc)Scatter-Gather.
* pwritev64: (libc)Scatter-Gather.
* pwritev64v2: (libc)Scatter-Gather.
* pwritev: (libc)Scatter-Gather.
* qecvt: (libc)System V Number Conversion.
* qecvt_r: (libc)System V Number Conversion.
* qfcvt: (libc)System V Number Conversion.
* qfcvt_r: (libc)System V Number Conversion.
* qgcvt: (libc)System V Number Conversion.
* qsort: (libc)Array Sort Function.
* raise: (libc)Signaling Yourself.
* rand: (libc)ISO Random.
* rand_r: (libc)ISO Random.
* random: (libc)BSD Random.
* random_r: (libc)BSD Random.
* rawmemchr: (libc)Search Functions.
* read: (libc)I/O Primitives.
* readdir64: (libc)Reading/Closing Directory.
* readdir64_r: (libc)Reading/Closing Directory.
* readdir: (libc)Reading/Closing Directory.
* readdir_r: (libc)Reading/Closing Directory.
* readlink: (libc)Symbolic Links.
* readv: (libc)Scatter-Gather.
* realloc: (libc)Changing Block Size.
* reallocarray: (libc)Changing Block Size.
* realpath: (libc)Symbolic Links.
* recv: (libc)Receiving Data.
* recvfrom: (libc)Receiving Datagrams.
* recvmsg: (libc)Receiving Datagrams.
* regcomp: (libc)POSIX Regexp Compilation.
* regerror: (libc)Regexp Cleanup.
* regexec: (libc)Matching POSIX Regexps.
* regfree: (libc)Regexp Cleanup.
* register_printf_function: (libc)Registering New Conversions.
* remainder: (libc)Remainder Functions.
* remainderf: (libc)Remainder Functions.
* remainderfN: (libc)Remainder Functions.
* remainderfNx: (libc)Remainder Functions.
* remainderl: (libc)Remainder Functions.
* remove: (libc)Deleting Files.
* rename: (libc)Renaming Files.
* rewind: (libc)File Positioning.
* rewinddir: (libc)Random Access Directory.
* rindex: (libc)Search Functions.
* rint: (libc)Rounding Functions.
* rintf: (libc)Rounding Functions.
* rintfN: (libc)Rounding Functions.
* rintfNx: (libc)Rounding Functions.
* rintl: (libc)Rounding Functions.
* rmdir: (libc)Deleting Files.
* round: (libc)Rounding Functions.
* roundeven: (libc)Rounding Functions.
* roundevenf: (libc)Rounding Functions.
* roundevenfN: (libc)Rounding Functions.
* roundevenfNx: (libc)Rounding Functions.
* roundevenl: (libc)Rounding Functions.
* roundf: (libc)Rounding Functions.
* roundfN: (libc)Rounding Functions.
* roundfNx: (libc)Rounding Functions.
* roundl: (libc)Rounding Functions.
* rpmatch: (libc)Yes-or-No Questions.
* sbrk: (libc)Resizing the Data Segment.
* scalb: (libc)Normalization Functions.
* scalbf: (libc)Normalization Functions.
* scalbl: (libc)Normalization Functions.
* scalbln: (libc)Normalization Functions.
* scalblnf: (libc)Normalization Functions.
* scalblnfN: (libc)Normalization Functions.
* scalblnfNx: (libc)Normalization Functions.
* scalblnl: (libc)Normalization Functions.
* scalbn: (libc)Normalization Functions.
* scalbnf: (libc)Normalization Functions.
* scalbnfN: (libc)Normalization Functions.
* scalbnfNx: (libc)Normalization Functions.
* scalbnl: (libc)Normalization Functions.
* scandir64: (libc)Scanning Directory Content.
* scandir: (libc)Scanning Directory Content.
* scanf: (libc)Formatted Input Functions.
* sched_get_priority_max: (libc)Basic Scheduling Functions.
* sched_get_priority_min: (libc)Basic Scheduling Functions.
* sched_getaffinity: (libc)CPU Affinity.
* sched_getparam: (libc)Basic Scheduling Functions.
* sched_getscheduler: (libc)Basic Scheduling Functions.
* sched_rr_get_interval: (libc)Basic Scheduling Functions.
* sched_setaffinity: (libc)CPU Affinity.
* sched_setparam: (libc)Basic Scheduling Functions.
* sched_setscheduler: (libc)Basic Scheduling Functions.
* sched_yield: (libc)Basic Scheduling Functions.
* secure_getenv: (libc)Environment Access.
* seed48: (libc)SVID Random.
* seed48_r: (libc)SVID Random.
* seekdir: (libc)Random Access Directory.
* select: (libc)Waiting for I/O.
* sem_clockwait: (libc)Default Thread Attributes.
* sem_close: (libc)Semaphores.
* sem_destroy: (libc)Semaphores.
* sem_getvalue: (libc)Semaphores.
* sem_init: (libc)Semaphores.
* sem_open: (libc)Semaphores.
* sem_post: (libc)Semaphores.
* sem_timedwait: (libc)Semaphores.
* sem_trywait: (libc)Semaphores.
* sem_unlink: (libc)Semaphores.
* sem_wait: (libc)Semaphores.
* semctl: (libc)Semaphores.
* semget: (libc)Semaphores.
* semop: (libc)Semaphores.
* semtimedop: (libc)Semaphores.
* send: (libc)Sending Data.
* sendmsg: (libc)Receiving Datagrams.
* sendto: (libc)Sending Datagrams.
* setbuf: (libc)Controlling Buffering.
* setbuffer: (libc)Controlling Buffering.
* setcontext: (libc)System V contexts.
* setdomainname: (libc)Host Identification.
* setegid: (libc)Setting Groups.
* setenv: (libc)Environment Access.
* seteuid: (libc)Setting User ID.
* setfsent: (libc)fstab.
* setgid: (libc)Setting Groups.
* setgrent: (libc)Scanning All Groups.
* setgroups: (libc)Setting Groups.
* sethostent: (libc)Host Names.
* sethostid: (libc)Host Identification.
* sethostname: (libc)Host Identification.
* setitimer: (libc)Setting an Alarm.
* setjmp: (libc)Non-Local Details.
* setlinebuf: (libc)Controlling Buffering.
* setlocale: (libc)Setting the Locale.
* setlogmask: (libc)setlogmask.
* setmntent: (libc)mtab.
* setnetent: (libc)Networks Database.
* setnetgrent: (libc)Lookup Netgroup.
* setpayload: (libc)FP Bit Twiddling.
* setpayloadf: (libc)FP Bit Twiddling.
* setpayloadfN: (libc)FP Bit Twiddling.
* setpayloadfNx: (libc)FP Bit Twiddling.
* setpayloadl: (libc)FP Bit Twiddling.
* setpayloadsig: (libc)FP Bit Twiddling.
* setpayloadsigf: (libc)FP Bit Twiddling.
* setpayloadsigfN: (libc)FP Bit Twiddling.
* setpayloadsigfNx: (libc)FP Bit Twiddling.
* setpayloadsigl: (libc)FP Bit Twiddling.
* setpgid: (libc)Process Group Functions.
* setpgrp: (libc)Process Group Functions.
* setpriority: (libc)Traditional Scheduling Functions.
* setprotoent: (libc)Protocols Database.
* setpwent: (libc)Scanning All Users.
* setregid: (libc)Setting Groups.
* setreuid: (libc)Setting User ID.
* setrlimit64: (libc)Limits on Resources.
* setrlimit: (libc)Limits on Resources.
* setservent: (libc)Services Database.
* setsid: (libc)Process Group Functions.
* setsockopt: (libc)Socket Option Functions.
* setstate: (libc)BSD Random.
* setstate_r: (libc)BSD Random.
* settimeofday: (libc)High-Resolution Calendar.
* setuid: (libc)Setting User ID.
* setutent: (libc)Manipulating the Database.
* setutxent: (libc)XPG Functions.
* setvbuf: (libc)Controlling Buffering.
* shm_open: (libc)Memory-mapped I/O.
* shm_unlink: (libc)Memory-mapped I/O.
* shutdown: (libc)Closing a Socket.
* sigaction: (libc)Advanced Signal Handling.
* sigaddset: (libc)Signal Sets.
* sigaltstack: (libc)Signal Stack.
* sigblock: (libc)BSD Signal Handling.
* sigdelset: (libc)Signal Sets.
* sigemptyset: (libc)Signal Sets.
* sigfillset: (libc)Signal Sets.
* siginterrupt: (libc)BSD Signal Handling.
* sigismember: (libc)Signal Sets.
* siglongjmp: (libc)Non-Local Exits and Signals.
* sigmask: (libc)BSD Signal Handling.
* signal: (libc)Basic Signal Handling.
* signbit: (libc)FP Bit Twiddling.
* significand: (libc)Normalization Functions.
* significandf: (libc)Normalization Functions.
* significandl: (libc)Normalization Functions.
* sigpause: (libc)BSD Signal Handling.
* sigpending: (libc)Checking for Pending Signals.
* sigprocmask: (libc)Process Signal Mask.
* sigsetjmp: (libc)Non-Local Exits and Signals.
* sigsetmask: (libc)BSD Signal Handling.
* sigstack: (libc)Signal Stack.
* sigsuspend: (libc)Sigsuspend.
* sin: (libc)Trig Functions.
* sincos: (libc)Trig Functions.
* sincosf: (libc)Trig Functions.
* sincosfN: (libc)Trig Functions.
* sincosfNx: (libc)Trig Functions.
* sincosl: (libc)Trig Functions.
* sinf: (libc)Trig Functions.
* sinfN: (libc)Trig Functions.
* sinfNx: (libc)Trig Functions.
* sinh: (libc)Hyperbolic Functions.
* sinhf: (libc)Hyperbolic Functions.
* sinhfN: (libc)Hyperbolic Functions.
* sinhfNx: (libc)Hyperbolic Functions.
* sinhl: (libc)Hyperbolic Functions.
* sinl: (libc)Trig Functions.
* sleep: (libc)Sleeping.
* snprintf: (libc)Formatted Output Functions.
* socket: (libc)Creating a Socket.
* socketpair: (libc)Socket Pairs.
* sprintf: (libc)Formatted Output Functions.
* sqrt: (libc)Exponents and Logarithms.
* sqrtf: (libc)Exponents and Logarithms.
* sqrtfN: (libc)Exponents and Logarithms.
* sqrtfNx: (libc)Exponents and Logarithms.
* sqrtl: (libc)Exponents and Logarithms.
* srand48: (libc)SVID Random.
* srand48_r: (libc)SVID Random.
* srand: (libc)ISO Random.
* srandom: (libc)BSD Random.
* srandom_r: (libc)BSD Random.
* sscanf: (libc)Formatted Input Functions.
* ssignal: (libc)Basic Signal Handling.
* stat64: (libc)Reading Attributes.
* stat: (libc)Reading Attributes.
* stime: (libc)Simple Calendar Time.
* stpcpy: (libc)Copying Strings and Arrays.
* stpncpy: (libc)Truncating Strings.
* strcasecmp: (libc)String/Array Comparison.
* strcasestr: (libc)Search Functions.
* strcat: (libc)Concatenating Strings.
* strchr: (libc)Search Functions.
* strchrnul: (libc)Search Functions.
* strcmp: (libc)String/Array Comparison.
* strcoll: (libc)Collation Functions.
* strcpy: (libc)Copying Strings and Arrays.
* strcspn: (libc)Search Functions.
* strdup: (libc)Copying Strings and Arrays.
* strdupa: (libc)Copying Strings and Arrays.
* strerror: (libc)Error Messages.
* strerror_r: (libc)Error Messages.
* strfmon: (libc)Formatting Numbers.
* strfromd: (libc)Printing of Floats.
* strfromf: (libc)Printing of Floats.
* strfromfN: (libc)Printing of Floats.
* strfromfNx: (libc)Printing of Floats.
* strfroml: (libc)Printing of Floats.
* strfry: (libc)Shuffling Bytes.
* strftime: (libc)Formatting Calendar Time.
* strlen: (libc)String Length.
* strncasecmp: (libc)String/Array Comparison.
* strncat: (libc)Truncating Strings.
* strncmp: (libc)String/Array Comparison.
* strncpy: (libc)Truncating Strings.
* strndup: (libc)Truncating Strings.
* strndupa: (libc)Truncating Strings.
* strnlen: (libc)String Length.
* strpbrk: (libc)Search Functions.
* strptime: (libc)Low-Level Time String Parsing.
* strrchr: (libc)Search Functions.
* strsep: (libc)Finding Tokens in a String.
* strsignal: (libc)Signal Messages.
* strspn: (libc)Search Functions.
* strstr: (libc)Search Functions.
* strtod: (libc)Parsing of Floats.
* strtof: (libc)Parsing of Floats.
* strtofN: (libc)Parsing of Floats.
* strtofNx: (libc)Parsing of Floats.
* strtoimax: (libc)Parsing of Integers.
* strtok: (libc)Finding Tokens in a String.
* strtok_r: (libc)Finding Tokens in a String.
* strtol: (libc)Parsing of Integers.
* strtold: (libc)Parsing of Floats.
* strtoll: (libc)Parsing of Integers.
* strtoq: (libc)Parsing of Integers.
* strtoul: (libc)Parsing of Integers.
* strtoull: (libc)Parsing of Integers.
* strtoumax: (libc)Parsing of Integers.
* strtouq: (libc)Parsing of Integers.
* strverscmp: (libc)String/Array Comparison.
* strxfrm: (libc)Collation Functions.
* stty: (libc)BSD Terminal Modes.
* swapcontext: (libc)System V contexts.
* swprintf: (libc)Formatted Output Functions.
* swscanf: (libc)Formatted Input Functions.
* symlink: (libc)Symbolic Links.
* sync: (libc)Synchronizing I/O.
* syscall: (libc)System Calls.
* sysconf: (libc)Sysconf Definition.
* sysctl: (libc)System Parameters.
* syslog: (libc)syslog; vsyslog.
* system: (libc)Running a Command.
* sysv_signal: (libc)Basic Signal Handling.
* tan: (libc)Trig Functions.
* tanf: (libc)Trig Functions.
* tanfN: (libc)Trig Functions.
* tanfNx: (libc)Trig Functions.
* tanh: (libc)Hyperbolic Functions.
* tanhf: (libc)Hyperbolic Functions.
* tanhfN: (libc)Hyperbolic Functions.
* tanhfNx: (libc)Hyperbolic Functions.
* tanhl: (libc)Hyperbolic Functions.
* tanl: (libc)Trig Functions.
* tcdrain: (libc)Line Control.
* tcflow: (libc)Line Control.
* tcflush: (libc)Line Control.
* tcgetattr: (libc)Mode Functions.
* tcgetpgrp: (libc)Terminal Access Functions.
* tcgetsid: (libc)Terminal Access Functions.
* tcsendbreak: (libc)Line Control.
* tcsetattr: (libc)Mode Functions.
* tcsetpgrp: (libc)Terminal Access Functions.
* tdelete: (libc)Tree Search Function.
* tdestroy: (libc)Tree Search Function.
* telldir: (libc)Random Access Directory.
* tempnam: (libc)Temporary Files.
* textdomain: (libc)Locating gettext catalog.
* tfind: (libc)Tree Search Function.
* tgamma: (libc)Special Functions.
* tgammaf: (libc)Special Functions.
* tgammafN: (libc)Special Functions.
* tgammafNx: (libc)Special Functions.
* tgammal: (libc)Special Functions.
* tgkill: (libc)Signaling Another Process.
* thrd_create: (libc)ISO C Thread Management.
* thrd_current: (libc)ISO C Thread Management.
* thrd_detach: (libc)ISO C Thread Management.
* thrd_equal: (libc)ISO C Thread Management.
* thrd_exit: (libc)ISO C Thread Management.
* thrd_join: (libc)ISO C Thread Management.
* thrd_sleep: (libc)ISO C Thread Management.
* thrd_yield: (libc)ISO C Thread Management.
* time: (libc)Simple Calendar Time.
* timegm: (libc)Broken-down Time.
* timelocal: (libc)Broken-down Time.
* times: (libc)Processor Time.
* tmpfile64: (libc)Temporary Files.
* tmpfile: (libc)Temporary Files.
* tmpnam: (libc)Temporary Files.
* tmpnam_r: (libc)Temporary Files.
* toascii: (libc)Case Conversion.
* tolower: (libc)Case Conversion.
* totalorder: (libc)FP Comparison Functions.
* totalorderf: (libc)FP Comparison Functions.
* totalorderfN: (libc)FP Comparison Functions.
* totalorderfNx: (libc)FP Comparison Functions.
* totalorderl: (libc)FP Comparison Functions.
* totalordermag: (libc)FP Comparison Functions.
* totalordermagf: (libc)FP Comparison Functions.
* totalordermagfN: (libc)FP Comparison Functions.
* totalordermagfNx: (libc)FP Comparison Functions.
* totalordermagl: (libc)FP Comparison Functions.
* toupper: (libc)Case Conversion.
* towctrans: (libc)Wide Character Case Conversion.
* towlower: (libc)Wide Character Case Conversion.
* towupper: (libc)Wide Character Case Conversion.
* trunc: (libc)Rounding Functions.
* truncate64: (libc)File Size.
* truncate: (libc)File Size.
* truncf: (libc)Rounding Functions.
* truncfN: (libc)Rounding Functions.
* truncfNx: (libc)Rounding Functions.
* truncl: (libc)Rounding Functions.
* tsearch: (libc)Tree Search Function.
* tss_create: (libc)ISO C Thread-local Storage.
* tss_delete: (libc)ISO C Thread-local Storage.
* tss_get: (libc)ISO C Thread-local Storage.
* tss_set: (libc)ISO C Thread-local Storage.
* ttyname: (libc)Is It a Terminal.
* ttyname_r: (libc)Is It a Terminal.
* twalk: (libc)Tree Search Function.
* twalk_r: (libc)Tree Search Function.
* tzset: (libc)Time Zone Functions.
* ufromfp: (libc)Rounding Functions.
* ufromfpf: (libc)Rounding Functions.
* ufromfpfN: (libc)Rounding Functions.
* ufromfpfNx: (libc)Rounding Functions.
* ufromfpl: (libc)Rounding Functions.
* ufromfpx: (libc)Rounding Functions.
* ufromfpxf: (libc)Rounding Functions.
* ufromfpxfN: (libc)Rounding Functions.
* ufromfpxfNx: (libc)Rounding Functions.
* ufromfpxl: (libc)Rounding Functions.
* ulimit: (libc)Limits on Resources.
* umask: (libc)Setting Permissions.
* umount2: (libc)Mount-Unmount-Remount.
* umount: (libc)Mount-Unmount-Remount.
* uname: (libc)Platform Type.
* ungetc: (libc)How Unread.
* ungetwc: (libc)How Unread.
* unlink: (libc)Deleting Files.
* unlockpt: (libc)Allocation.
* unsetenv: (libc)Environment Access.
* updwtmp: (libc)Manipulating the Database.
* utime: (libc)File Times.
* utimes: (libc)File Times.
* utmpname: (libc)Manipulating the Database.
* utmpxname: (libc)XPG Functions.
* va_arg: (libc)Argument Macros.
* va_copy: (libc)Argument Macros.
* va_end: (libc)Argument Macros.
* va_start: (libc)Argument Macros.
* valloc: (libc)Aligned Memory Blocks.
* vasprintf: (libc)Variable Arguments Output.
* verr: (libc)Error Messages.
* verrx: (libc)Error Messages.
* versionsort64: (libc)Scanning Directory Content.
* versionsort: (libc)Scanning Directory Content.
* vfork: (libc)Creating a Process.
* vfprintf: (libc)Variable Arguments Output.
* vfscanf: (libc)Variable Arguments Input.
* vfwprintf: (libc)Variable Arguments Output.
* vfwscanf: (libc)Variable Arguments Input.
* vlimit: (libc)Limits on Resources.
* vprintf: (libc)Variable Arguments Output.
* vscanf: (libc)Variable Arguments Input.
* vsnprintf: (libc)Variable Arguments Output.
* vsprintf: (libc)Variable Arguments Output.
* vsscanf: (libc)Variable Arguments Input.
* vswprintf: (libc)Variable Arguments Output.
* vswscanf: (libc)Variable Arguments Input.
* vsyslog: (libc)syslog; vsyslog.
* vtimes: (libc)Resource Usage.
* vwarn: (libc)Error Messages.
* vwarnx: (libc)Error Messages.
* vwprintf: (libc)Variable Arguments Output.
* vwscanf: (libc)Variable Arguments Input.
* wait3: (libc)BSD Wait Functions.
* wait4: (libc)Process Completion.
* wait: (libc)Process Completion.
* waitpid: (libc)Process Completion.
* warn: (libc)Error Messages.
* warnx: (libc)Error Messages.
* wcpcpy: (libc)Copying Strings and Arrays.
* wcpncpy: (libc)Truncating Strings.
* wcrtomb: (libc)Converting a Character.
* wcscasecmp: (libc)String/Array Comparison.
* wcscat: (libc)Concatenating Strings.
* wcschr: (libc)Search Functions.
* wcschrnul: (libc)Search Functions.
* wcscmp: (libc)String/Array Comparison.
* wcscoll: (libc)Collation Functions.
* wcscpy: (libc)Copying Strings and Arrays.
* wcscspn: (libc)Search Functions.
* wcsdup: (libc)Copying Strings and Arrays.
* wcsftime: (libc)Formatting Calendar Time.
* wcslen: (libc)String Length.
* wcsncasecmp: (libc)String/Array Comparison.
* wcsncat: (libc)Truncating Strings.
* wcsncmp: (libc)String/Array Comparison.
* wcsncpy: (libc)Truncating Strings.
* wcsnlen: (libc)String Length.
* wcsnrtombs: (libc)Converting Strings.
* wcspbrk: (libc)Search Functions.
* wcsrchr: (libc)Search Functions.
* wcsrtombs: (libc)Converting Strings.
* wcsspn: (libc)Search Functions.
* wcsstr: (libc)Search Functions.
* wcstod: (libc)Parsing of Floats.
* wcstof: (libc)Parsing of Floats.
* wcstofN: (libc)Parsing of Floats.
* wcstofNx: (libc)Parsing of Floats.
* wcstoimax: (libc)Parsing of Integers.
* wcstok: (libc)Finding Tokens in a String.
* wcstol: (libc)Parsing of Integers.
* wcstold: (libc)Parsing of Floats.
* wcstoll: (libc)Parsing of Integers.
* wcstombs: (libc)Non-reentrant String Conversion.
* wcstoq: (libc)Parsing of Integers.
* wcstoul: (libc)Parsing of Integers.
* wcstoull: (libc)Parsing of Integers.
* wcstoumax: (libc)Parsing of Integers.
* wcstouq: (libc)Parsing of Integers.
* wcswcs: (libc)Search Functions.
* wcsxfrm: (libc)Collation Functions.
* wctob: (libc)Converting a Character.
* wctomb: (libc)Non-reentrant Character Conversion.
* wctrans: (libc)Wide Character Case Conversion.
* wctype: (libc)Classification of Wide Characters.
* wmemchr: (libc)Search Functions.
* wmemcmp: (libc)String/Array Comparison.
* wmemcpy: (libc)Copying Strings and Arrays.
* wmemmove: (libc)Copying Strings and Arrays.
* wmempcpy: (libc)Copying Strings and Arrays.
* wmemset: (libc)Copying Strings and Arrays.
* wordexp: (libc)Calling Wordexp.
* wordfree: (libc)Calling Wordexp.
* wprintf: (libc)Formatted Output Functions.
* write: (libc)I/O Primitives.
* writev: (libc)Scatter-Gather.
* wscanf: (libc)Formatted Input Functions.
* y0: (libc)Special Functions.
* y0f: (libc)Special Functions.
* y0fN: (libc)Special Functions.
* y0fNx: (libc)Special Functions.
* y0l: (libc)Special Functions.
* y1: (libc)Special Functions.
* y1f: (libc)Special Functions.
* y1fN: (libc)Special Functions.
* y1fNx: (libc)Special Functions.
* y1l: (libc)Special Functions.
* yn: (libc)Special Functions.
* ynf: (libc)Special Functions.
* ynfN: (libc)Special Functions.
* ynfNx: (libc)Special Functions.
* ynl: (libc)Special Functions.
END-INFO-DIR-ENTRY


File: libc.info,  Node: Line Input,  Next: Unreading,  Prev: Character Input,  Up: I/O on Streams

12.9 Line-Oriented Input
========================

Since many programs interpret input on the basis of lines, it is
convenient to have functions to read a line of text from a stream.

   Standard C has functions to do this, but they aren’t very safe: null
characters and even (for ‘gets’) long lines can confuse them.  So the
GNU C Library provides the nonstandard ‘getline’ function that makes it
easy to read lines reliably.

   Another GNU extension, ‘getdelim’, generalizes ‘getline’.  It reads a
delimited record, defined as everything through the next occurrence of a
specified delimiter character.

   All these functions are declared in ‘stdio.h’.

 -- Function: ssize_t getline (char **LINEPTR, size_t *N, FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt heap | AC-Unsafe lock
     corrupt mem | *Note POSIX Safety Concepts::.

     This function reads an entire line from STREAM, storing the text
     (including the newline and a terminating null character) in a
     buffer and storing the buffer address in ‘*LINEPTR’.

     Before calling ‘getline’, you should place in ‘*LINEPTR’ the
     address of a buffer ‘*N’ bytes long, allocated with ‘malloc’.  If
     this buffer is long enough to hold the line, ‘getline’ stores the
     line in this buffer.  Otherwise, ‘getline’ makes the buffer bigger
     using ‘realloc’, storing the new buffer address back in ‘*LINEPTR’
     and the increased size back in ‘*N’.  *Note Unconstrained
     Allocation::.

     If you set ‘*LINEPTR’ to a null pointer, and ‘*N’ to zero, before
     the call, then ‘getline’ allocates the initial buffer for you by
     calling ‘malloc’.  This buffer remains allocated even if ‘getline’
     encounters errors and is unable to read any bytes.

     In either case, when ‘getline’ returns, ‘*LINEPTR’ is a ‘char *’
     which points to the text of the line.

     When ‘getline’ is successful, it returns the number of characters
     read (including the newline, but not including the terminating
     null).  This value enables you to distinguish null characters that
     are part of the line from the null character inserted as a
     terminator.

     This function is a GNU extension, but it is the recommended way to
     read lines from a stream.  The alternative standard functions are
     unreliable.

     If an error occurs or end of file is reached without any bytes
     read, ‘getline’ returns ‘-1’.

 -- Function: ssize_t getdelim (char **LINEPTR, size_t *N, int
          DELIMITER, FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt heap | AC-Unsafe lock
     corrupt mem | *Note POSIX Safety Concepts::.

     This function is like ‘getline’ except that the character which
     tells it to stop reading is not necessarily newline.  The argument
     DELIMITER specifies the delimiter character; ‘getdelim’ keeps
     reading until it sees that character (or end of file).

     The text is stored in LINEPTR, including the delimiter character
     and a terminating null.  Like ‘getline’, ‘getdelim’ makes LINEPTR
     bigger if it isn’t big enough.

     ‘getline’ is in fact implemented in terms of ‘getdelim’, just like
     this:

          ssize_t
          getline (char **lineptr, size_t *n, FILE *stream)
          {
            return getdelim (lineptr, n, '\n', stream);
          }

 -- Function: char * fgets (char *S, int COUNT, FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘fgets’ function reads characters from the stream STREAM up to
     and including a newline character and stores them in the string S,
     adding a null character to mark the end of the string.  You must
     supply COUNT characters worth of space in S, but the number of
     characters read is at most COUNT − 1.  The extra character space is
     used to hold the null character at the end of the string.

     If the system is already at end of file when you call ‘fgets’, then
     the contents of the array S are unchanged and a null pointer is
     returned.  A null pointer is also returned if a read error occurs.
     Otherwise, the return value is the pointer S.

     *Warning:* If the input data has a null character, you can’t tell.
     So don’t use ‘fgets’ unless you know the data cannot contain a
     null.  Don’t use it to read files edited by the user because, if
     the user inserts a null character, you should either handle it
     properly or print a clear error message.  We recommend using
     ‘getline’ instead of ‘fgets’.

 -- Function: wchar_t * fgetws (wchar_t *WS, int COUNT, FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘fgetws’ function reads wide characters from the stream STREAM
     up to and including a newline character and stores them in the
     string WS, adding a null wide character to mark the end of the
     string.  You must supply COUNT wide characters worth of space in
     WS, but the number of characters read is at most COUNT − 1.  The
     extra character space is used to hold the null wide character at
     the end of the string.

     If the system is already at end of file when you call ‘fgetws’,
     then the contents of the array WS are unchanged and a null pointer
     is returned.  A null pointer is also returned if a read error
     occurs.  Otherwise, the return value is the pointer WS.

     *Warning:* If the input data has a null wide character (which are
     null bytes in the input stream), you can’t tell.  So don’t use
     ‘fgetws’ unless you know the data cannot contain a null.  Don’t use
     it to read files edited by the user because, if the user inserts a
     null character, you should either handle it properly or print a
     clear error message.

 -- Function: char * fgets_unlocked (char *S, int COUNT, FILE *STREAM)

     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fgets_unlocked’ function is equivalent to the ‘fgets’ function
     except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: wchar_t * fgetws_unlocked (wchar_t *WS, int COUNT, FILE
          *STREAM)

     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fgetws_unlocked’ function is equivalent to the ‘fgetws’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Deprecated function: char * gets (char *S)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The function ‘gets’ reads characters from the stream ‘stdin’ up to
     the next newline character, and stores them in the string S.  The
     newline character is discarded (note that this differs from the
     behavior of ‘fgets’, which copies the newline character into the
     string).  If ‘gets’ encounters a read error or end-of-file, it
     returns a null pointer; otherwise it returns S.

     *Warning:* The ‘gets’ function is *very dangerous* because it
     provides no protection against overflowing the string S.  The GNU C
     Library includes it for compatibility only.  You should *always*
     use ‘fgets’ or ‘getline’ instead.  To remind you of this, the
     linker (if using GNU ‘ld’) will issue a warning whenever you use
     ‘gets’.


File: libc.info,  Node: Unreading,  Next: Block Input/Output,  Prev: Line Input,  Up: I/O on Streams

12.10 Unreading
===============

In parser programs it is often useful to examine the next character in
the input stream without removing it from the stream.  This is called
“peeking ahead” at the input because your program gets a glimpse of the
input it will read next.

   Using stream I/O, you can peek ahead at input by first reading it and
then "unreading" it (also called "pushing it back" on the stream).
Unreading a character makes it available to be input again from the
stream, by the next call to ‘fgetc’ or other input function on that
stream.

* Menu:

* Unreading Idea::              An explanation of unreading with pictures.
* How Unread::                  How to call ‘ungetc’ to do unreading.


File: libc.info,  Node: Unreading Idea,  Next: How Unread,  Up: Unreading

12.10.1 What Unreading Means
----------------------------

Here is a pictorial explanation of unreading.  Suppose you have a stream
reading a file that contains just six characters, the letters ‘foobar’.
Suppose you have read three characters so far.  The situation looks like
this:

     f  o  o  b  a  r
     	 ^

so the next input character will be ‘b’.

   If instead of reading ‘b’ you unread the letter ‘o’, you get a
situation like this:

     f  o  o  b  a  r
     	 |
           o--
           ^

so that the next input characters will be ‘o’ and ‘b’.

   If you unread ‘9’ instead of ‘o’, you get this situation:

     f  o  o  b  a  r
     	 |
           9--
           ^

so that the next input characters will be ‘9’ and ‘b’.


File: libc.info,  Node: How Unread,  Prev: Unreading Idea,  Up: Unreading

12.10.2 Using ‘ungetc’ To Do Unreading
--------------------------------------

The function to unread a character is called ‘ungetc’, because it
reverses the action of ‘getc’.

 -- Function: int ungetc (int C, FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘ungetc’ function pushes back the character C onto the input
     stream STREAM.  So the next input from STREAM will read C before
     anything else.

     If C is ‘EOF’, ‘ungetc’ does nothing and just returns ‘EOF’.  This
     lets you call ‘ungetc’ with the return value of ‘getc’ without
     needing to check for an error from ‘getc’.

     The character that you push back doesn’t have to be the same as the
     last character that was actually read from the stream.  In fact, it
     isn’t necessary to actually read any characters from the stream
     before unreading them with ‘ungetc’!  But that is a strange way to
     write a program; usually ‘ungetc’ is used only to unread a
     character that was just read from the same stream.  The GNU C
     Library supports this even on files opened in binary mode, but
     other systems might not.

     The GNU C Library only supports one character of pushback—in other
     words, it does not work to call ‘ungetc’ twice without doing input
     in between.  Other systems might let you push back multiple
     characters; then reading from the stream retrieves the characters
     in the reverse order that they were pushed.

     Pushing back characters doesn’t alter the file; only the internal
     buffering for the stream is affected.  If a file positioning
     function (such as ‘fseek’, ‘fseeko’ or ‘rewind’; *note File
     Positioning::) is called, any pending pushed-back characters are
     discarded.

     Unreading a character on a stream that is at end of file clears the
     end-of-file indicator for the stream, because it makes the
     character of input available.  After you read that character,
     trying to read again will encounter end of file.

 -- Function: wint_t ungetwc (wint_t WC, FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘ungetwc’ function behaves just like ‘ungetc’ just that it
     pushes back a wide character.

   Here is an example showing the use of ‘getc’ and ‘ungetc’ to skip
over whitespace characters.  When this function reaches a non-whitespace
character, it unreads that character to be seen again on the next read
operation on the stream.

     #include <stdio.h>
     #include <ctype.h>

     void
     skip_whitespace (FILE *stream)
     {
       int c;
       do
         /* No need to check for ‘EOF’ because it is not
            ‘isspace’, and ‘ungetc’ ignores ‘EOF’.  */
         c = getc (stream);
       while (isspace (c));
       ungetc (c, stream);
     }


File: libc.info,  Node: Block Input/Output,  Next: Formatted Output,  Prev: Unreading,  Up: I/O on Streams

12.11 Block Input/Output
========================

This section describes how to do input and output operations on blocks
of data.  You can use these functions to read and write binary data, as
well as to read and write text in fixed-size blocks instead of by
characters or lines.

   Binary files are typically used to read and write blocks of data in
the same format as is used to represent the data in a running program.
In other words, arbitrary blocks of memory—not just character or string
objects—can be written to a binary file, and meaningfully read in again
by the same program.

   Storing data in binary form is often considerably more efficient than
using the formatted I/O functions.  Also, for floating-point numbers,
the binary form avoids possible loss of precision in the conversion
process.  On the other hand, binary files can’t be examined or modified
easily using many standard file utilities (such as text editors), and
are not portable between different implementations of the language, or
different kinds of computers.

   These functions are declared in ‘stdio.h’.

 -- Function: size_t fread (void *DATA, size_t SIZE, size_t COUNT, FILE
          *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function reads up to COUNT objects of size SIZE into the array
     DATA, from the stream STREAM.  It returns the number of objects
     actually read, which might be less than COUNT if a read error
     occurs or the end of the file is reached.  This function returns a
     value of zero (and doesn’t read anything) if either SIZE or COUNT
     is zero.

     If ‘fread’ encounters end of file in the middle of an object, it
     returns the number of complete objects read, and discards the
     partial object.  Therefore, the stream remains at the actual end of
     the file.

 -- Function: size_t fread_unlocked (void *DATA, size_t SIZE, size_t
          COUNT, FILE *STREAM)

     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fread_unlocked’ function is equivalent to the ‘fread’ function
     except that it does not implicitly lock the stream.

     This function is a GNU extension.

 -- Function: size_t fwrite (const void *DATA, size_t SIZE, size_t
          COUNT, FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function writes up to COUNT objects of size SIZE from the
     array DATA, to the stream STREAM.  The return value is normally
     COUNT, if the call succeeds.  Any other value indicates some sort
     of error, such as running out of space.

 -- Function: size_t fwrite_unlocked (const void *DATA, size_t SIZE,
          size_t COUNT, FILE *STREAM)

     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fwrite_unlocked’ function is equivalent to the ‘fwrite’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.


File: libc.info,  Node: Formatted Output,  Next: Customizing Printf,  Prev: Block Input/Output,  Up: I/O on Streams

12.12 Formatted Output
======================

The functions described in this section (‘printf’ and related functions)
provide a convenient way to perform formatted output.  You call ‘printf’
with a "format string" or "template string" that specifies how to format
the values of the remaining arguments.

   Unless your program is a filter that specifically performs line- or
character-oriented processing, using ‘printf’ or one of the other
related functions described in this section is usually the easiest and
most concise way to perform output.  These functions are especially
useful for printing error messages, tables of data, and the like.

* Menu:

* Formatted Output Basics::     Some examples to get you started.
* Output Conversion Syntax::    General syntax of conversion
				 specifications.
* Table of Output Conversions:: Summary of output conversions and
				 what they do.
* Integer Conversions::         Details about formatting of integers.
* Floating-Point Conversions::  Details about formatting of
				 floating-point numbers.
* Other Output Conversions::    Details about formatting of strings,
				 characters, pointers, and the like.
* Formatted Output Functions::  Descriptions of the actual functions.
* Dynamic Output::		Functions that allocate memory for the output.
* Variable Arguments Output::   ‘vprintf’ and friends.
* Parsing a Template String::   What kinds of args does a given template
				 call for?
* Example of Parsing::          Sample program using ‘parse_printf_format’.


File: libc.info,  Node: Formatted Output Basics,  Next: Output Conversion Syntax,  Up: Formatted Output

12.12.1 Formatted Output Basics
-------------------------------

The ‘printf’ function can be used to print any number of arguments.  The
template string argument you supply in a call provides information not
only about the number of additional arguments, but also about their
types and what style should be used for printing them.

   Ordinary characters in the template string are simply written to the
output stream as-is, while "conversion specifications" introduced by a
‘%’ character in the template cause subsequent arguments to be formatted
and written to the output stream.  For example,

     int pct = 37;
     char filename[] = "foo.txt";
     printf ("Processing of `%s' is %d%% finished.\nPlease be patient.\n",
     	filename, pct);

produces output like

     Processing of `foo.txt' is 37% finished.
     Please be patient.

   This example shows the use of the ‘%d’ conversion to specify that an
‘int’ argument should be printed in decimal notation, the ‘%s’
conversion to specify printing of a string argument, and the ‘%%’
conversion to print a literal ‘%’ character.

   There are also conversions for printing an integer argument as an
unsigned value in octal, decimal, or hexadecimal radix (‘%o’, ‘%u’, or
‘%x’, respectively); or as a character value (‘%c’).

   Floating-point numbers can be printed in normal, fixed-point notation
using the ‘%f’ conversion or in exponential notation using the ‘%e’
conversion.  The ‘%g’ conversion uses either ‘%e’ or ‘%f’ format,
depending on what is more appropriate for the magnitude of the
particular number.

   You can control formatting more precisely by writing "modifiers"
between the ‘%’ and the character that indicates which conversion to
apply.  These slightly alter the ordinary behavior of the conversion.
For example, most conversion specifications permit you to specify a
minimum field width and a flag indicating whether you want the result
left- or right-justified within the field.

   The specific flags and modifiers that are permitted and their
interpretation vary depending on the particular conversion.  They’re all
described in more detail in the following sections.  Don’t worry if this
all seems excessively complicated at first; you can almost always get
reasonable free-format output without using any of the modifiers at all.
The modifiers are mostly used to make the output look “prettier” in
tables.


File: libc.info,  Node: Output Conversion Syntax,  Next: Table of Output Conversions,  Prev: Formatted Output Basics,  Up: Formatted Output

12.12.2 Output Conversion Syntax
--------------------------------

This section provides details about the precise syntax of conversion
specifications that can appear in a ‘printf’ template string.

   Characters in the template string that are not part of a conversion
specification are printed as-is to the output stream.  Multibyte
character sequences (*note Character Set Handling::) are permitted in a
template string.

   The conversion specifications in a ‘printf’ template string have the
general form:

     % [ PARAM-NO $] FLAGS WIDTH [ . PRECISION ] TYPE CONVERSION

or

     % [ PARAM-NO $] FLAGS WIDTH . * [ PARAM-NO $] TYPE CONVERSION

   For example, in the conversion specifier ‘%-10.8ld’, the ‘-’ is a
flag, ‘10’ specifies the field width, the precision is ‘8’, the letter
‘l’ is a type modifier, and ‘d’ specifies the conversion style.  (This
particular type specifier says to print a ‘long int’ argument in decimal
notation, with a minimum of 8 digits left-justified in a field at least
10 characters wide.)

   In more detail, output conversion specifications consist of an
initial ‘%’ character followed in sequence by:

   • An optional specification of the parameter used for this format.
     Normally the parameters to the ‘printf’ function are assigned to
     the formats in the order of appearance in the format string.  But
     in some situations (such as message translation) this is not
     desirable and this extension allows an explicit parameter to be
     specified.

     The PARAM-NO parts of the format must be integers in the range of 1
     to the maximum number of arguments present to the function call.
     Some implementations limit this number to a certain upper bound.
     The exact limit can be retrieved by the following constant.

      -- Macro: NL_ARGMAX
          The value of ‘NL_ARGMAX’ is the maximum value allowed for the
          specification of a positional parameter in a ‘printf’ call.
          The actual value in effect at runtime can be retrieved by
          using ‘sysconf’ using the ‘_SC_NL_ARGMAX’ parameter *note
          Sysconf Definition::.

          Some systems have a quite low limit such as 9 for System V
          systems.  The GNU C Library has no real limit.

     If any of the formats has a specification for the parameter
     position all of them in the format string shall have one.
     Otherwise the behavior is undefined.

   • Zero or more "flag characters" that modify the normal behavior of
     the conversion specification.

   • An optional decimal integer specifying the "minimum field width".
     If the normal conversion produces fewer characters than this, the
     field is padded with spaces to the specified width.  This is a
     _minimum_ value; if the normal conversion produces more characters
     than this, the field is _not_ truncated.  Normally, the output is
     right-justified within the field.

     You can also specify a field width of ‘*’.  This means that the
     next argument in the argument list (before the actual value to be
     printed) is used as the field width.  The value must be an ‘int’.
     If the value is negative, this means to set the ‘-’ flag (see
     below) and to use the absolute value as the field width.

   • An optional "precision" to specify the number of digits to be
     written for the numeric conversions.  If the precision is
     specified, it consists of a period (‘.’) followed optionally by a
     decimal integer (which defaults to zero if omitted).

     You can also specify a precision of ‘*’.  This means that the next
     argument in the argument list (before the actual value to be
     printed) is used as the precision.  The value must be an ‘int’, and
     is ignored if it is negative.  If you specify ‘*’ for both the
     field width and precision, the field width argument precedes the
     precision argument.  Other C library versions may not recognize
     this syntax.

   • An optional "type modifier character", which is used to specify the
     data type of the corresponding argument if it differs from the
     default type.  (For example, the integer conversions assume a type
     of ‘int’, but you can specify ‘h’, ‘l’, or ‘L’ for other integer
     types.)

   • A character that specifies the conversion to be applied.

   The exact options that are permitted and how they are interpreted
vary between the different conversion specifiers.  See the descriptions
of the individual conversions for information about the particular
options that they use.

   With the ‘-Wformat’ option, the GNU C compiler checks calls to
‘printf’ and related functions.  It examines the format string and
verifies that the correct number and types of arguments are supplied.
There is also a GNU C syntax to tell the compiler that a function you
write uses a ‘printf’-style format string.  *Note Declaring Attributes
of Functions: (gcc)Function Attributes, for more information.


File: libc.info,  Node: Table of Output Conversions,  Next: Integer Conversions,  Prev: Output Conversion Syntax,  Up: Formatted Output

12.12.3 Table of Output Conversions
-----------------------------------

Here is a table summarizing what all the different conversions do:

‘%d’, ‘%i’
     Print an integer as a signed decimal number.  *Note Integer
     Conversions::, for details.  ‘%d’ and ‘%i’ are synonymous for
     output, but are different when used with ‘scanf’ for input (*note
     Table of Input Conversions::).

‘%o’
     Print an integer as an unsigned octal number.  *Note Integer
     Conversions::, for details.

‘%u’
     Print an integer as an unsigned decimal number.  *Note Integer
     Conversions::, for details.

‘%x’, ‘%X’
     Print an integer as an unsigned hexadecimal number.  ‘%x’ uses
     lower-case letters and ‘%X’ uses upper-case.  *Note Integer
     Conversions::, for details.

‘%f’
     Print a floating-point number in normal (fixed-point) notation.
     *Note Floating-Point Conversions::, for details.

‘%e’, ‘%E’
     Print a floating-point number in exponential notation.  ‘%e’ uses
     lower-case letters and ‘%E’ uses upper-case.  *Note Floating-Point
     Conversions::, for details.

‘%g’, ‘%G’
     Print a floating-point number in either normal or exponential
     notation, whichever is more appropriate for its magnitude.  ‘%g’
     uses lower-case letters and ‘%G’ uses upper-case.  *Note
     Floating-Point Conversions::, for details.

‘%a’, ‘%A’
     Print a floating-point number in a hexadecimal fractional notation
     with the exponent to base 2 represented in decimal digits.  ‘%a’
     uses lower-case letters and ‘%A’ uses upper-case.  *Note
     Floating-Point Conversions::, for details.

‘%c’
     Print a single character.  *Note Other Output Conversions::.

‘%C’
     This is an alias for ‘%lc’ which is supported for compatibility
     with the Unix standard.

‘%s’
     Print a string.  *Note Other Output Conversions::.

‘%S’
     This is an alias for ‘%ls’ which is supported for compatibility
     with the Unix standard.

‘%p’
     Print the value of a pointer.  *Note Other Output Conversions::.

‘%n’
     Get the number of characters printed so far.  *Note Other Output
     Conversions::.  Note that this conversion specification never
     produces any output.

‘%m’
     Print the string corresponding to the value of ‘errno’.  (This is a
     GNU extension.)  *Note Other Output Conversions::.

‘%%’
     Print a literal ‘%’ character.  *Note Other Output Conversions::.

   If the syntax of a conversion specification is invalid, unpredictable
things will happen, so don’t do this.  If there aren’t enough function
arguments provided to supply values for all the conversion
specifications in the template string, or if the arguments are not of
the correct types, the results are unpredictable.  If you supply more
arguments than conversion specifications, the extra argument values are
simply ignored; this is sometimes useful.


File: libc.info,  Node: Integer Conversions,  Next: Floating-Point Conversions,  Prev: Table of Output Conversions,  Up: Formatted Output

12.12.4 Integer Conversions
---------------------------

This section describes the options for the ‘%d’, ‘%i’, ‘%o’, ‘%u’, ‘%x’,
and ‘%X’ conversion specifications.  These conversions print integers in
various formats.

   The ‘%d’ and ‘%i’ conversion specifications both print an ‘int’
argument as a signed decimal number; while ‘%o’, ‘%u’, and ‘%x’ print
the argument as an unsigned octal, decimal, or hexadecimal number
(respectively).  The ‘%X’ conversion specification is just like ‘%x’
except that it uses the characters ‘ABCDEF’ as digits instead of
‘abcdef’.

   The following flags are meaningful:

‘-’
     Left-justify the result in the field (instead of the normal
     right-justification).

‘+’
     For the signed ‘%d’ and ‘%i’ conversions, print a plus sign if the
     value is positive.

‘ ’
     For the signed ‘%d’ and ‘%i’ conversions, if the result doesn’t
     start with a plus or minus sign, prefix it with a space character
     instead.  Since the ‘+’ flag ensures that the result includes a
     sign, this flag is ignored if you supply both of them.

‘#’
     For the ‘%o’ conversion, this forces the leading digit to be ‘0’,
     as if by increasing the precision.  For ‘%x’ or ‘%X’, this prefixes
     a leading ‘0x’ or ‘0X’ (respectively) to the result.  This doesn’t
     do anything useful for the ‘%d’, ‘%i’, or ‘%u’ conversions.  Using
     this flag produces output which can be parsed by the ‘strtoul’
     function (*note Parsing of Integers::) and ‘scanf’ with the ‘%i’
     conversion (*note Numeric Input Conversions::).

‘'’
     Separate the digits into groups as specified by the locale
     specified for the ‘LC_NUMERIC’ category; *note General Numeric::.
     This flag is a GNU extension.

‘0’
     Pad the field with zeros instead of spaces.  The zeros are placed
     after any indication of sign or base.  This flag is ignored if the
     ‘-’ flag is also specified, or if a precision is specified.

   If a precision is supplied, it specifies the minimum number of digits
to appear; leading zeros are produced if necessary.  If you don’t
specify a precision, the number is printed with as many digits as it
needs.  If you convert a value of zero with an explicit precision of
zero, then no characters at all are produced.

   Without a type modifier, the corresponding argument is treated as an
‘int’ (for the signed conversions ‘%i’ and ‘%d’) or ‘unsigned int’ (for
the unsigned conversions ‘%o’, ‘%u’, ‘%x’, and ‘%X’).  Recall that since
‘printf’ and friends are variadic, any ‘char’ and ‘short’ arguments are
automatically converted to ‘int’ by the default argument promotions.
For arguments of other integer types, you can use these modifiers:

‘hh’
     Specifies that the argument is a ‘signed char’ or ‘unsigned char’,
     as appropriate.  A ‘char’ argument is converted to an ‘int’ or
     ‘unsigned int’ by the default argument promotions anyway, but the
     ‘hh’ modifier says to convert it back to a ‘char’ again.

     This modifier was introduced in ISO C99.

‘h’
     Specifies that the argument is a ‘short int’ or ‘unsigned short
     int’, as appropriate.  A ‘short’ argument is converted to an ‘int’
     or ‘unsigned int’ by the default argument promotions anyway, but
     the ‘h’ modifier says to convert it back to a ‘short’ again.

‘j’
     Specifies that the argument is a ‘intmax_t’ or ‘uintmax_t’, as
     appropriate.

     This modifier was introduced in ISO C99.

‘l’
     Specifies that the argument is a ‘long int’ or ‘unsigned long int’,
     as appropriate.  Two ‘l’ characters are like the ‘L’ modifier,
     below.

     If used with ‘%c’ or ‘%s’ the corresponding parameter is considered
     as a wide character or wide character string respectively.  This
     use of ‘l’ was introduced in Amendment 1 to ISO C90.

‘L’
‘ll’
‘q’
     Specifies that the argument is a ‘long long int’.  (This type is an
     extension supported by the GNU C compiler.  On systems that don’t
     support extra-long integers, this is the same as ‘long int’.)

     The ‘q’ modifier is another name for the same thing, which comes
     from 4.4 BSD; a ‘long long int’ is sometimes called a “quad” ‘int’.

‘t’
     Specifies that the argument is a ‘ptrdiff_t’.

     This modifier was introduced in ISO C99.

‘z’
‘Z’
     Specifies that the argument is a ‘size_t’.

     ‘z’ was introduced in ISO C99.  ‘Z’ is a GNU extension predating
     this addition and should not be used in new code.

   Here is an example.  Using the template string:

     "|%5d|%-5d|%+5d|%+-5d|% 5d|%05d|%5.0d|%5.2d|%d|\n"

to print numbers using the different options for the ‘%d’ conversion
gives results like:

     |    0|0    |   +0|+0   |    0|00000|     |   00|0|
     |    1|1    |   +1|+1   |    1|00001|    1|   01|1|
     |   -1|-1   |   -1|-1   |   -1|-0001|   -1|  -01|-1|
     |100000|100000|+100000|+100000| 100000|100000|100000|100000|100000|

   In particular, notice what happens in the last case where the number
is too large to fit in the minimum field width specified.

   Here are some more examples showing how unsigned integers print under
various format options, using the template string:

     "|%5u|%5o|%5x|%5X|%#5o|%#5x|%#5X|%#10.8x|\n"

     |    0|    0|    0|    0|    0|    0|    0|  00000000|
     |    1|    1|    1|    1|   01|  0x1|  0X1|0x00000001|
     |100000|303240|186a0|186A0|0303240|0x186a0|0X186A0|0x000186a0|


File: libc.info,  Node: Floating-Point Conversions,  Next: Other Output Conversions,  Prev: Integer Conversions,  Up: Formatted Output

12.12.5 Floating-Point Conversions
----------------------------------

This section discusses the conversion specifications for floating-point
numbers: the ‘%f’, ‘%e’, ‘%E’, ‘%g’, and ‘%G’ conversions.

   The ‘%f’ conversion prints its argument in fixed-point notation,
producing output of the form [‘-’]DDD‘.’DDD, where the number of digits
following the decimal point is controlled by the precision you specify.

   The ‘%e’ conversion prints its argument in exponential notation,
producing output of the form [‘-’]D‘.’DDD‘e’[‘+’|‘-’]DD.  Again, the
number of digits following the decimal point is controlled by the
precision.  The exponent always contains at least two digits.  The ‘%E’
conversion is similar but the exponent is marked with the letter ‘E’
instead of ‘e’.

   The ‘%g’ and ‘%G’ conversions print the argument in the style of ‘%e’
or ‘%E’ (respectively) if the exponent would be less than -4 or greater
than or equal to the precision; otherwise they use the ‘%f’ style.  A
precision of ‘0’, is taken as 1.  Trailing zeros are removed from the
fractional portion of the result and a decimal-point character appears
only if it is followed by a digit.

   The ‘%a’ and ‘%A’ conversions are meant for representing
floating-point numbers exactly in textual form so that they can be
exchanged as texts between different programs and/or machines.  The
numbers are represented in the form [‘-’]‘0x’H‘.’HHH‘p’[‘+’|‘-’]DD.  At
the left of the decimal-point character exactly one digit is print.
This character is only ‘0’ if the number is denormalized.  Otherwise the
value is unspecified; it is implementation dependent how many bits are
used.  The number of hexadecimal digits on the right side of the
decimal-point character is equal to the precision.  If the precision is
zero it is determined to be large enough to provide an exact
representation of the number (or it is large enough to distinguish two
adjacent values if the ‘FLT_RADIX’ is not a power of 2, *note Floating
Point Parameters::).  For the ‘%a’ conversion lower-case characters are
used to represent the hexadecimal number and the prefix and exponent
sign are printed as ‘0x’ and ‘p’ respectively.  Otherwise upper-case
characters are used and ‘0X’ and ‘P’ are used for the representation of
prefix and exponent string.  The exponent to the base of two is printed
as a decimal number using at least one digit but at most as many digits
as necessary to represent the value exactly.

   If the value to be printed represents infinity or a NaN, the output
is [‘-’]‘inf’ or ‘nan’ respectively if the conversion specifier is ‘%a’,
‘%e’, ‘%f’, or ‘%g’ and it is [‘-’]‘INF’ or ‘NAN’ respectively if the
conversion is ‘%A’, ‘%E’, or ‘%G’.

   The following flags can be used to modify the behavior:

‘-’
     Left-justify the result in the field.  Normally the result is
     right-justified.

‘+’
     Always include a plus or minus sign in the result.

‘ ’
     If the result doesn’t start with a plus or minus sign, prefix it
     with a space instead.  Since the ‘+’ flag ensures that the result
     includes a sign, this flag is ignored if you supply both of them.

‘#’
     Specifies that the result should always include a decimal point,
     even if no digits follow it.  For the ‘%g’ and ‘%G’ conversions,
     this also forces trailing zeros after the decimal point to be left
     in place where they would otherwise be removed.

‘'’
     Separate the digits of the integer part of the result into groups
     as specified by the locale specified for the ‘LC_NUMERIC’ category;
     *note General Numeric::.  This flag is a GNU extension.

‘0’
     Pad the field with zeros instead of spaces; the zeros are placed
     after any sign.  This flag is ignored if the ‘-’ flag is also
     specified.

   The precision specifies how many digits follow the decimal-point
character for the ‘%f’, ‘%e’, and ‘%E’ conversions.  For these
conversions, the default precision is ‘6’.  If the precision is
explicitly ‘0’, this suppresses the decimal point character entirely.
For the ‘%g’ and ‘%G’ conversions, the precision specifies how many
significant digits to print.  Significant digits are the first digit
before the decimal point, and all the digits after it.  If the precision
is ‘0’ or not specified for ‘%g’ or ‘%G’, it is treated like a value of
‘1’.  If the value being printed cannot be expressed accurately in the
specified number of digits, the value is rounded to the nearest number
that fits.

   Without a type modifier, the floating-point conversions use an
argument of type ‘double’.  (By the default argument promotions, any
‘float’ arguments are automatically converted to ‘double’.)  The
following type modifier is supported:

‘L’
     An uppercase ‘L’ specifies that the argument is a ‘long double’.

   Here are some examples showing how numbers print using the various
floating-point conversions.  All of the numbers were printed using this
template string:

     "|%13.4a|%13.4f|%13.4e|%13.4g|\n"

   Here is the output:

     |  0x0.0000p+0|       0.0000|   0.0000e+00|            0|
     |  0x1.0000p-1|       0.5000|   5.0000e-01|          0.5|
     |  0x1.0000p+0|       1.0000|   1.0000e+00|            1|
     | -0x1.0000p+0|      -1.0000|  -1.0000e+00|           -1|
     |  0x1.9000p+6|     100.0000|   1.0000e+02|          100|
     |  0x1.f400p+9|    1000.0000|   1.0000e+03|         1000|
     | 0x1.3880p+13|   10000.0000|   1.0000e+04|        1e+04|
     | 0x1.81c8p+13|   12345.0000|   1.2345e+04|    1.234e+04|
     | 0x1.86a0p+16|  100000.0000|   1.0000e+05|        1e+05|
     | 0x1.e240p+16|  123456.0000|   1.2346e+05|    1.235e+05|

   Notice how the ‘%g’ conversion drops trailing zeros.


File: libc.info,  Node: Other Output Conversions,  Next: Formatted Output Functions,  Prev: Floating-Point Conversions,  Up: Formatted Output

12.12.6 Other Output Conversions
--------------------------------

This section describes miscellaneous conversions for ‘printf’.

   The ‘%c’ conversion prints a single character.  In case there is no
‘l’ modifier the ‘int’ argument is first converted to an ‘unsigned
char’.  Then, if used in a wide stream function, the character is
converted into the corresponding wide character.  The ‘-’ flag can be
used to specify left-justification in the field, but no other flags are
defined, and no precision or type modifier can be given.  For example:

     printf ("%c%c%c%c%c", 'h', 'e', 'l', 'l', 'o');

prints ‘hello’.

   If there is an ‘l’ modifier present the argument is expected to be of
type ‘wint_t’.  If used in a multibyte function the wide character is
converted into a multibyte character before being added to the output.
In this case more than one output byte can be produced.

   The ‘%s’ conversion prints a string.  If no ‘l’ modifier is present
the corresponding argument must be of type ‘char *’ (or ‘const char *’).
If used in a wide stream function the string is first converted to a
wide character string.  A precision can be specified to indicate the
maximum number of characters to write; otherwise characters in the
string up to but not including the terminating null character are
written to the output stream.  The ‘-’ flag can be used to specify
left-justification in the field, but no other flags or type modifiers
are defined for this conversion.  For example:

     printf ("%3s%-6s", "no", "where");

prints ‘ nowhere ’.

   If there is an ‘l’ modifier present, the argument is expected to be
of type ‘wchar_t’ (or ‘const wchar_t *’).

   If you accidentally pass a null pointer as the argument for a ‘%s’
conversion, the GNU C Library prints it as ‘(null)’.  We think this is
more useful than crashing.  But it’s not good practice to pass a null
argument intentionally.

   The ‘%m’ conversion prints the string corresponding to the error code
in ‘errno’.  *Note Error Messages::.  Thus:

     fprintf (stderr, "can't open `%s': %m\n", filename);

is equivalent to:

     fprintf (stderr, "can't open `%s': %s\n", filename, strerror (errno));

The ‘%m’ conversion is a GNU C Library extension.

   The ‘%p’ conversion prints a pointer value.  The corresponding
argument must be of type ‘void *’.  In practice, you can use any type of
pointer.

   In the GNU C Library, non-null pointers are printed as unsigned
integers, as if a ‘%#x’ conversion were used.  Null pointers print as
‘(nil)’.  (Pointers might print differently in other systems.)

   For example:

     printf ("%p", "testing");

prints ‘0x’ followed by a hexadecimal number—the address of the string
constant ‘"testing"’.  It does not print the word ‘testing’.

   You can supply the ‘-’ flag with the ‘%p’ conversion to specify
left-justification, but no other flags, precision, or type modifiers are
defined.

   The ‘%n’ conversion is unlike any of the other output conversions.
It uses an argument which must be a pointer to an ‘int’, but instead of
printing anything it stores the number of characters printed so far by
this call at that location.  The ‘h’ and ‘l’ type modifiers are
permitted to specify that the argument is of type ‘short int *’ or ‘long
int *’ instead of ‘int *’, but no flags, field width, or precision are
permitted.

   For example,

     int nchar;
     printf ("%d %s%n\n", 3, "bears", &nchar);

prints:

     3 bears

and sets ‘nchar’ to ‘7’, because ‘3 bears’ is seven characters.

   The ‘%%’ conversion prints a literal ‘%’ character.  This conversion
doesn’t use an argument, and no flags, field width, precision, or type
modifiers are permitted.


File: libc.info,  Node: Formatted Output Functions,  Next: Dynamic Output,  Prev: Other Output Conversions,  Up: Formatted Output

12.12.7 Formatted Output Functions
----------------------------------

This section describes how to call ‘printf’ and related functions.
Prototypes for these functions are in the header file ‘stdio.h’.
Because these functions take a variable number of arguments, you _must_
declare prototypes for them before using them.  Of course, the easiest
way to make sure you have all the right prototypes is to just include
‘stdio.h’.

 -- Function: int printf (const char *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     The ‘printf’ function prints the optional arguments under the
     control of the template string TEMPLATE to the stream ‘stdout’.  It
     returns the number of characters printed, or a negative value if
     there was an output error.

 -- Function: int wprintf (const wchar_t *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     The ‘wprintf’ function prints the optional arguments under the
     control of the wide template string TEMPLATE to the stream
     ‘stdout’.  It returns the number of wide characters printed, or a
     negative value if there was an output error.

 -- Function: int fprintf (FILE *STREAM, const char *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is just like ‘printf’, except that the output is
     written to the stream STREAM instead of ‘stdout’.

 -- Function: int fwprintf (FILE *STREAM, const wchar_t *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is just like ‘wprintf’, except that the output is
     written to the stream STREAM instead of ‘stdout’.

 -- Function: int sprintf (char *S, const char *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is like ‘printf’, except that the output is stored in the
     character array S instead of written to a stream.  A null character
     is written to mark the end of the string.

     The ‘sprintf’ function returns the number of characters stored in
     the array S, not including the terminating null character.

     The behavior of this function is undefined if copying takes place
     between objects that overlap—for example, if S is also given as an
     argument to be printed under control of the ‘%s’ conversion.  *Note
     Copying Strings and Arrays::.

     *Warning:* The ‘sprintf’ function can be *dangerous* because it can
     potentially output more characters than can fit in the allocation
     size of the string S.  Remember that the field width given in a
     conversion specification is only a _minimum_ value.

     To avoid this problem, you can use ‘snprintf’ or ‘asprintf’,
     described below.

 -- Function: int swprintf (wchar_t *WS, size_t SIZE, const wchar_t
          *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is like ‘wprintf’, except that the output is stored in the
     wide character array WS instead of written to a stream.  A null
     wide character is written to mark the end of the string.  The SIZE
     argument specifies the maximum number of characters to produce.
     The trailing null character is counted towards this limit, so you
     should allocate at least SIZE wide characters for the string WS.

     The return value is the number of characters generated for the
     given input, excluding the trailing null.  If not all output fits
     into the provided buffer a negative value is returned.  You should
     try again with a bigger output string.  _Note:_ this is different
     from how ‘snprintf’ handles this situation.

     Note that the corresponding narrow stream function takes fewer
     parameters.  ‘swprintf’ in fact corresponds to the ‘snprintf’
     function.  Since the ‘sprintf’ function can be dangerous and should
     be avoided the ISO C committee refused to make the same mistake
     again and decided to not define a function exactly corresponding to
     ‘sprintf’.

 -- Function: int snprintf (char *S, size_t SIZE, const char *TEMPLATE,
          …)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     The ‘snprintf’ function is similar to ‘sprintf’, except that the
     SIZE argument specifies the maximum number of characters to
     produce.  The trailing null character is counted towards this
     limit, so you should allocate at least SIZE characters for the
     string S.  If SIZE is zero, nothing, not even the null byte, shall
     be written and S may be a null pointer.

     The return value is the number of characters which would be
     generated for the given input, excluding the trailing null.  If
     this value is greater than or equal to SIZE, not all characters
     from the result have been stored in S.  You should try again with a
     bigger output string.  Here is an example of doing this:

          /* Construct a message describing the value of a variable
             whose name is NAME and whose value is VALUE. */
          char *
          make_message (char *name, char *value)
          {
            /* Guess we need no more than 100 chars of space. */
            int size = 100;
            char *buffer = (char *) xmalloc (size);
            int nchars;
            if (buffer == NULL)
              return NULL;

           /* Try to print in the allocated space. */
            nchars = snprintf (buffer, size, "value of %s is %s",
          		     name, value);
            if (nchars >= size)
              {
                /* Reallocate buffer now that we know
          	 how much space is needed. */
                size = nchars + 1;
                buffer = (char *) xrealloc (buffer, size);

                if (buffer != NULL)
          	/* Try again. */
          	snprintf (buffer, size, "value of %s is %s",
          		  name, value);
              }
            /* The last call worked, return the string. */
            return buffer;
          }

     In practice, it is often easier just to use ‘asprintf’, below.

     *Attention:* In versions of the GNU C Library prior to 2.1 the
     return value is the number of characters stored, not including the
     terminating null; unless there was not enough space in S to store
     the result in which case ‘-1’ is returned.  This was changed in
     order to comply with the ISO C99 standard.


File: libc.info,  Node: Dynamic Output,  Next: Variable Arguments Output,  Prev: Formatted Output Functions,  Up: Formatted Output

12.12.8 Dynamically Allocating Formatted Output
-----------------------------------------------

The functions in this section do formatted output and place the results
in dynamically allocated memory.

 -- Function: int asprintf (char **PTR, const char *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This function is similar to ‘sprintf’, except that it dynamically
     allocates a string (as with ‘malloc’; *note Unconstrained
     Allocation::) to hold the output, instead of putting the output in
     a buffer you allocate in advance.  The PTR argument should be the
     address of a ‘char *’ object, and a successful call to ‘asprintf’
     stores a pointer to the newly allocated string at that location.

     The return value is the number of characters allocated for the
     buffer, or less than zero if an error occurred.  Usually this means
     that the buffer could not be allocated.

     Here is how to use ‘asprintf’ to get the same result as the
     ‘snprintf’ example, but more easily:

          /* Construct a message describing the value of a variable
             whose name is NAME and whose value is VALUE. */
          char *
          make_message (char *name, char *value)
          {
            char *result;
            if (asprintf (&result, "value of %s is %s", name, value) < 0)
              return NULL;
            return result;
          }

 -- Function: int obstack_printf (struct obstack *OBSTACK, const char
          *TEMPLATE, …)

     Preliminary: | MT-Safe race:obstack locale | AS-Unsafe corrupt heap
     | AC-Unsafe corrupt mem | *Note POSIX Safety Concepts::.

     This function is similar to ‘asprintf’, except that it uses the
     obstack OBSTACK to allocate the space.  *Note Obstacks::.

     The characters are written onto the end of the current object.  To
     get at them, you must finish the object with ‘obstack_finish’
     (*note Growing Objects::).


File: libc.info,  Node: Variable Arguments Output,  Next: Parsing a Template String,  Prev: Dynamic Output,  Up: Formatted Output

12.12.9 Variable Arguments Output Functions
-------------------------------------------

The functions ‘vprintf’ and friends are provided so that you can define
your own variadic ‘printf’-like functions that make use of the same
internals as the built-in formatted output functions.

   The most natural way to define such functions would be to use a
language construct to say, “Call ‘printf’ and pass this template plus
all of my arguments after the first five.” But there is no way to do
this in C, and it would be hard to provide a way, since at the C
language level there is no way to tell how many arguments your function
received.

   Since that method is impossible, we provide alternative functions,
the ‘vprintf’ series, which lets you pass a ‘va_list’ to describe “all
of my arguments after the first five.”

   When it is sufficient to define a macro rather than a real function,
the GNU C compiler provides a way to do this much more easily with
macros.  For example:

     #define myprintf(a, b, c, d, e, rest...) \
     	    printf (mytemplate , ## rest)

*Note (cpp)Variadic Macros::, for details.  But this is limited to
macros, and does not apply to real functions at all.

   Before calling ‘vprintf’ or the other functions listed in this
section, you _must_ call ‘va_start’ (*note Variadic Functions::) to
initialize a pointer to the variable arguments.  Then you can call
‘va_arg’ to fetch the arguments that you want to handle yourself.  This
advances the pointer past those arguments.

   Once your ‘va_list’ pointer is pointing at the argument of your
choice, you are ready to call ‘vprintf’.  That argument and all
subsequent arguments that were passed to your function are used by
‘vprintf’ along with the template that you specified separately.

   *Portability Note:* The value of the ‘va_list’ pointer is
undetermined after the call to ‘vprintf’, so you must not use ‘va_arg’
after you call ‘vprintf’.  Instead, you should call ‘va_end’ to retire
the pointer from service.  You can call ‘va_start’ again and begin
fetching the arguments from the start of the variable argument list.
(Alternatively, you can use ‘va_copy’ to make a copy of the ‘va_list’
pointer before calling ‘vfprintf’.)  Calling ‘vprintf’ does not destroy
the argument list of your function, merely the particular pointer that
you passed to it.

   Prototypes for these functions are declared in ‘stdio.h’.

 -- Function: int vprintf (const char *TEMPLATE, va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is similar to ‘printf’ except that, instead of taking
     a variable number of arguments directly, it takes an argument list
     pointer AP.

 -- Function: int vwprintf (const wchar_t *TEMPLATE, va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is similar to ‘wprintf’ except that, instead of
     taking a variable number of arguments directly, it takes an
     argument list pointer AP.

 -- Function: int vfprintf (FILE *STREAM, const char *TEMPLATE, va_list
          AP)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This is the equivalent of ‘fprintf’ with the variable argument list
     specified directly as for ‘vprintf’.

 -- Function: int vfwprintf (FILE *STREAM, const wchar_t *TEMPLATE,
          va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This is the equivalent of ‘fwprintf’ with the variable argument
     list specified directly as for ‘vwprintf’.

 -- Function: int vsprintf (char *S, const char *TEMPLATE, va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is the equivalent of ‘sprintf’ with the variable argument list
     specified directly as for ‘vprintf’.

 -- Function: int vswprintf (wchar_t *WS, size_t SIZE, const wchar_t
          *TEMPLATE, va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is the equivalent of ‘swprintf’ with the variable argument
     list specified directly as for ‘vwprintf’.

 -- Function: int vsnprintf (char *S, size_t SIZE, const char *TEMPLATE,
          va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is the equivalent of ‘snprintf’ with the variable argument
     list specified directly as for ‘vprintf’.

 -- Function: int vasprintf (char **PTR, const char *TEMPLATE, va_list
          AP)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     The ‘vasprintf’ function is the equivalent of ‘asprintf’ with the
     variable argument list specified directly as for ‘vprintf’.

 -- Function: int obstack_vprintf (struct obstack *OBSTACK, const char
          *TEMPLATE, va_list AP)

     Preliminary: | MT-Safe race:obstack locale | AS-Unsafe corrupt heap
     | AC-Unsafe corrupt mem | *Note POSIX Safety Concepts::.

     The ‘obstack_vprintf’ function is the equivalent of
     ‘obstack_printf’ with the variable argument list specified directly
     as for ‘vprintf’.

   Here’s an example showing how you might use ‘vfprintf’.  This is a
function that prints error messages to the stream ‘stderr’, along with a
prefix indicating the name of the program (*note Error Messages::, for a
description of ‘program_invocation_short_name’).

     #include <stdio.h>
     #include <stdarg.h>

     void
     eprintf (const char *template, ...)
     {
       va_list ap;
       extern char *program_invocation_short_name;

       fprintf (stderr, "%s: ", program_invocation_short_name);
       va_start (ap, template);
       vfprintf (stderr, template, ap);
       va_end (ap);
     }

You could call ‘eprintf’ like this:

     eprintf ("file `%s' does not exist\n", filename);

   In GNU C, there is a special construct you can use to let the
compiler know that a function uses a ‘printf’-style format string.  Then
it can check the number and types of arguments in each call to the
function, and warn you when they do not match the format string.  For
example, take this declaration of ‘eprintf’:

     void eprintf (const char *template, ...)
     	__attribute__ ((format (printf, 1, 2)));

This tells the compiler that ‘eprintf’ uses a format string like
‘printf’ (as opposed to ‘scanf’; *note Formatted Input::); the format
string appears as the first argument; and the arguments to satisfy the
format begin with the second.  *Note Declaring Attributes of Functions:
(gcc)Function Attributes, for more information.


File: libc.info,  Node: Parsing a Template String,  Next: Example of Parsing,  Prev: Variable Arguments Output,  Up: Formatted Output

12.12.10 Parsing a Template String
----------------------------------

You can use the function ‘parse_printf_format’ to obtain information
about the number and types of arguments that are expected by a given
template string.  This function permits interpreters that provide
interfaces to ‘printf’ to avoid passing along invalid arguments from the
user’s program, which could cause a crash.

   All the symbols described in this section are declared in the header
file ‘printf.h’.

 -- Function: size_t parse_printf_format (const char *TEMPLATE, size_t
          N, int *ARGTYPES)

     Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX
     Safety Concepts::.

     This function returns information about the number and types of
     arguments expected by the ‘printf’ template string TEMPLATE.  The
     information is stored in the array ARGTYPES; each element of this
     array describes one argument.  This information is encoded using
     the various ‘PA_’ macros, listed below.

     The argument N specifies the number of elements in the array
     ARGTYPES.  This is the maximum number of elements that
     ‘parse_printf_format’ will try to write.

     ‘parse_printf_format’ returns the total number of arguments
     required by TEMPLATE.  If this number is greater than N, then the
     information returned describes only the first N arguments.  If you
     want information about additional arguments, allocate a bigger
     array and call ‘parse_printf_format’ again.

   The argument types are encoded as a combination of a basic type and
modifier flag bits.

 -- Macro: int PA_FLAG_MASK

     This macro is a bitmask for the type modifier flag bits.  You can
     write the expression ‘(argtypes[i] & PA_FLAG_MASK)’ to extract just
     the flag bits for an argument, or ‘(argtypes[i] & ~PA_FLAG_MASK)’
     to extract just the basic type code.

   Here are symbolic constants that represent the basic types; they
stand for integer values.

‘PA_INT’

     This specifies that the base type is ‘int’.

‘PA_CHAR’

     This specifies that the base type is ‘int’, cast to ‘char’.

‘PA_STRING’

     This specifies that the base type is ‘char *’, a null-terminated
     string.

‘PA_POINTER’

     This specifies that the base type is ‘void *’, an arbitrary
     pointer.

‘PA_FLOAT’

     This specifies that the base type is ‘float’.

‘PA_DOUBLE’

     This specifies that the base type is ‘double’.

‘PA_LAST’

     You can define additional base types for your own programs as
     offsets from ‘PA_LAST’.  For example, if you have data types ‘foo’
     and ‘bar’ with their own specialized ‘printf’ conversions, you
     could define encodings for these types as:

          #define PA_FOO  PA_LAST
          #define PA_BAR  (PA_LAST + 1)

   Here are the flag bits that modify a basic type.  They are combined
with the code for the basic type using inclusive-or.

‘PA_FLAG_PTR’

     If this bit is set, it indicates that the encoded type is a pointer
     to the base type, rather than an immediate value.  For example,
     ‘PA_INT|PA_FLAG_PTR’ represents the type ‘int *’.

‘PA_FLAG_SHORT’

     If this bit is set, it indicates that the base type is modified
     with ‘short’.  (This corresponds to the ‘h’ type modifier.)

‘PA_FLAG_LONG’

     If this bit is set, it indicates that the base type is modified
     with ‘long’.  (This corresponds to the ‘l’ type modifier.)

‘PA_FLAG_LONG_LONG’

     If this bit is set, it indicates that the base type is modified
     with ‘long long’.  (This corresponds to the ‘L’ type modifier.)

‘PA_FLAG_LONG_DOUBLE’

     This is a synonym for ‘PA_FLAG_LONG_LONG’, used by convention with
     a base type of ‘PA_DOUBLE’ to indicate a type of ‘long double’.

   For an example of using these facilities, see *note Example of
Parsing::.


File: libc.info,  Node: Example of Parsing,  Prev: Parsing a Template String,  Up: Formatted Output

12.12.11 Example of Parsing a Template String
---------------------------------------------

Here is an example of decoding argument types for a format string.  We
assume this is part of an interpreter which contains arguments of type
‘NUMBER’, ‘CHAR’, ‘STRING’ and ‘STRUCTURE’ (and perhaps others which are
not valid here).

     /* Test whether the NARGS specified objects
        in the vector ARGS are valid
        for the format string FORMAT:
        if so, return 1.
        If not, return 0 after printing an error message.  */

     int
     validate_args (char *format, int nargs, OBJECT *args)
     {
       int *argtypes;
       int nwanted;

       /* Get the information about the arguments.
          Each conversion specification must be at least two characters
          long, so there cannot be more specifications than half the
          length of the string.  */

       argtypes = (int *) alloca (strlen (format) / 2 * sizeof (int));
       nwanted = parse_printf_format (string, nelts, argtypes);

       /* Check the number of arguments.  */
       if (nwanted > nargs)
         {
           error ("too few arguments (at least %d required)", nwanted);
           return 0;
         }

       /* Check the C type wanted for each argument
          and see if the object given is suitable.  */
       for (i = 0; i < nwanted; i++)
         {
           int wanted;

           if (argtypes[i] & PA_FLAG_PTR)
     	wanted = STRUCTURE;
           else
     	switch (argtypes[i] & ~PA_FLAG_MASK)
	       {
     	  case PA_INT:
     	  case PA_FLOAT:
     	  case PA_DOUBLE:
     	    wanted = NUMBER;
     	    break;
     	  case PA_CHAR:
     	    wanted = CHAR;
     	    break;
     	  case PA_STRING:
     	    wanted = STRING;
     	    break;
     	  case PA_POINTER:
     	    wanted = STRUCTURE;
     	    break;
	       }
           if (TYPE (args[i]) != wanted)
	     {
     	  error ("type mismatch for arg number %d", i);
     	  return 0;
	     }
         }
       return 1;
     }


File: libc.info,  Node: Customizing Printf,  Next: Formatted Input,  Prev: Formatted Output,  Up: I/O on Streams

12.13 Customizing ‘printf’
==========================

The GNU C Library lets you define your own custom conversion specifiers
for ‘printf’ template strings, to teach ‘printf’ clever ways to print
the important data structures of your program.

   The way you do this is by registering the conversion with the
function ‘register_printf_function’; see *note Registering New
Conversions::.  One of the arguments you pass to this function is a
pointer to a handler function that produces the actual output; see *note
Defining the Output Handler::, for information on how to write this
function.

   You can also install a function that just returns information about
the number and type of arguments expected by the conversion specifier.
*Note Parsing a Template String::, for information about this.

   The facilities of this section are declared in the header file
‘printf.h’.

* Menu:

* Registering New Conversions::         Using ‘register_printf_function’
					 to register a new output conversion.
* Conversion Specifier Options::        The handler must be able to get
					 the options specified in the
					 template when it is called.
* Defining the Output Handler::         Defining the handler and arginfo
					 functions that are passed as arguments
					 to ‘register_printf_function’.
* Printf Extension Example::            How to define a ‘printf’
					 handler function.
* Predefined Printf Handlers::          Predefined ‘printf’ handlers.

   *Portability Note:* The ability to extend the syntax of ‘printf’
template strings is a GNU extension.  ISO standard C has nothing
similar.  When using the GNU C compiler or any other compiler that
interprets calls to standard I/O functions according to the rules of the
language standard it is necessary to disable such handling by the
appropriate compiler option.  Otherwise the behavior of a program that
relies on the extension is undefined.


File: libc.info,  Node: Registering New Conversions,  Next: Conversion Specifier Options,  Up: Customizing Printf

12.13.1 Registering New Conversions
-----------------------------------

The function to register a new output conversion is
‘register_printf_function’, declared in ‘printf.h’.

 -- Function: int register_printf_function (int SPEC, printf_function
          HANDLER-FUNCTION, printf_arginfo_function ARGINFO-FUNCTION)

     Preliminary: | MT-Unsafe const:printfext | AS-Unsafe heap lock |
     AC-Unsafe mem lock | *Note POSIX Safety Concepts::.

     This function defines the conversion specifier character SPEC.
     Thus, if SPEC is ‘'Y'’, it defines the conversion ‘%Y’.  You can
     redefine the built-in conversions like ‘%s’, but flag characters
     like ‘#’ and type modifiers like ‘l’ can never be used as
     conversions; calling ‘register_printf_function’ for those
     characters has no effect.  It is advisable not to use lowercase
     letters, since the ISO C standard warns that additional lowercase
     letters may be standardized in future editions of the standard.

     The HANDLER-FUNCTION is the function called by ‘printf’ and friends
     when this conversion appears in a template string.  *Note Defining
     the Output Handler::, for information about how to define a
     function to pass as this argument.  If you specify a null pointer,
     any existing handler function for SPEC is removed.

     The ARGINFO-FUNCTION is the function called by
     ‘parse_printf_format’ when this conversion appears in a template
     string.  *Note Parsing a Template String::, for information about
     this.

     *Attention:* In the GNU C Library versions before 2.0 the
     ARGINFO-FUNCTION function did not need to be installed unless the
     user used the ‘parse_printf_format’ function.  This has changed.
     Now a call to any of the ‘printf’ functions will call this function
     when this format specifier appears in the format string.

     The return value is ‘0’ on success, and ‘-1’ on failure (which
     occurs if SPEC is out of range).

     *Portability Note:* It is possible to redefine the standard output
     conversions but doing so is strongly discouraged because it may
     interfere with the behavior of programs and compiler
     implementations that assume the effects of the conversions conform
     to the relevant language standards.  In addition, conforming
     compilers need not guarantee that the function registered for a
     standard conversion will be called for each such conversion in
     every format string in a program.


File: libc.info,  Node: Conversion Specifier Options,  Next: Defining the Output Handler,  Prev: Registering New Conversions,  Up: Customizing Printf

12.13.2 Conversion Specifier Options
------------------------------------

If you define a meaning for ‘%A’, what if the template contains ‘%+23A’
or ‘%-#A’?  To implement a sensible meaning for these, the handler when
called needs to be able to get the options specified in the template.

   Both the HANDLER-FUNCTION and ARGINFO-FUNCTION accept an argument
that points to a ‘struct printf_info’, which contains information about
the options appearing in an instance of the conversion specifier.  This
data type is declared in the header file ‘printf.h’.

 -- Type: struct printf_info

     This structure is used to pass information about the options
     appearing in an instance of a conversion specifier in a ‘printf’
     template string to the handler and arginfo functions for that
     specifier.  It contains the following members:

     ‘int prec’
          This is the precision specified.  The value is ‘-1’ if no
          precision was specified.  If the precision was given as ‘*’,
          the ‘printf_info’ structure passed to the handler function
          contains the actual value retrieved from the argument list.
          But the structure passed to the arginfo function contains a
          value of ‘INT_MIN’, since the actual value is not known.

     ‘int width’
          This is the minimum field width specified.  The value is ‘0’
          if no width was specified.  If the field width was given as
          ‘*’, the ‘printf_info’ structure passed to the handler
          function contains the actual value retrieved from the argument
          list.  But the structure passed to the arginfo function
          contains a value of ‘INT_MIN’, since the actual value is not
          known.

     ‘wchar_t spec’
          This is the conversion specifier character specified.  It’s
          stored in the structure so that you can register the same
          handler function for multiple characters, but still have a way
          to tell them apart when the handler function is called.

     ‘unsigned int is_long_double’
          This is a boolean that is true if the ‘L’, ‘ll’, or ‘q’ type
          modifier was specified.  For integer conversions, this
          indicates ‘long long int’, as opposed to ‘long double’ for
          floating point conversions.

     ‘unsigned int is_char’
          This is a boolean that is true if the ‘hh’ type modifier was
          specified.

     ‘unsigned int is_short’
          This is a boolean that is true if the ‘h’ type modifier was
          specified.

     ‘unsigned int is_long’
          This is a boolean that is true if the ‘l’ type modifier was
          specified.

     ‘unsigned int alt’
          This is a boolean that is true if the ‘#’ flag was specified.

     ‘unsigned int space’
          This is a boolean that is true if the ‘ ’ flag was specified.

     ‘unsigned int left’
          This is a boolean that is true if the ‘-’ flag was specified.

     ‘unsigned int showsign’
          This is a boolean that is true if the ‘+’ flag was specified.

     ‘unsigned int group’
          This is a boolean that is true if the ‘'’ flag was specified.

     ‘unsigned int extra’
          This flag has a special meaning depending on the context.  It
          could be used freely by the user-defined handlers but when
          called from the ‘printf’ function this variable always
          contains the value ‘0’.

     ‘unsigned int wide’
          This flag is set if the stream is wide oriented.

     ‘wchar_t pad’
          This is the character to use for padding the output to the
          minimum field width.  The value is ‘'0'’ if the ‘0’ flag was
          specified, and ‘' '’ otherwise.


File: libc.info,  Node: Defining the Output Handler,  Next: Printf Extension Example,  Prev: Conversion Specifier Options,  Up: Customizing Printf

12.13.3 Defining the Output Handler
-----------------------------------

Now let’s look at how to define the handler and arginfo functions which
are passed as arguments to ‘register_printf_function’.

   *Compatibility Note:* The interface changed in the GNU C Library
version 2.0.  Previously the third argument was of type ‘va_list *’.

   You should define your handler functions with a prototype like:

     int FUNCTION (FILE *stream, const struct printf_info *info,
     		    const void *const *args)

   The STREAM argument passed to the handler function is the stream to
which it should write output.

   The INFO argument is a pointer to a structure that contains
information about the various options that were included with the
conversion in the template string.  You should not modify this structure
inside your handler function.  *Note Conversion Specifier Options::, for
a description of this data structure.

   The ARGS is a vector of pointers to the arguments data.  The number
of arguments was determined by calling the argument information function
provided by the user.

   Your handler function should return a value just like ‘printf’ does:
it should return the number of characters it has written, or a negative
value to indicate an error.

 -- Data Type: printf_function

     This is the data type that a handler function should have.

   If you are going to use ‘parse_printf_format’ in your application,
you must also define a function to pass as the ARGINFO-FUNCTION argument
for each new conversion you install with ‘register_printf_function’.

   You have to define these functions with a prototype like:

     int FUNCTION (const struct printf_info *info,
     		    size_t n, int *argtypes)

   The return value from the function should be the number of arguments
the conversion expects.  The function should also fill in no more than N
elements of the ARGTYPES array with information about the types of each
of these arguments.  This information is encoded using the various ‘PA_’
macros.  (You will notice that this is the same calling convention
‘parse_printf_format’ itself uses.)

 -- Data Type: printf_arginfo_function

     This type is used to describe functions that return information
     about the number and type of arguments used by a conversion
     specifier.


File: libc.info,  Node: Printf Extension Example,  Next: Predefined Printf Handlers,  Prev: Defining the Output Handler,  Up: Customizing Printf

12.13.4 ‘printf’ Extension Example
----------------------------------

Here is an example showing how to define a ‘printf’ handler function.
This program defines a data structure called a ‘Widget’ and defines the
‘%W’ conversion to print information about ‘Widget *’ arguments,
including the pointer value and the name stored in the data structure.
The ‘%W’ conversion supports the minimum field width and
left-justification options, but ignores everything else.


     #include <stdio.h>
     #include <stdlib.h>
     #include <printf.h>

     typedef struct
     {
       char *name;
     }
     Widget;

     int
     print_widget (FILE *stream,
                   const struct printf_info *info,
                   const void *const *args)
     {
       const Widget *w;
       char *buffer;
       int len;

       /* Format the output into a string. */
       w = *((const Widget **) (args[0]));
       len = asprintf (&buffer, "<Widget %p: %s>", w, w->name);
       if (len == -1)
         return -1;

       /* Pad to the minimum field width and print to the stream. */
       len = fprintf (stream, "%*s",
                      (info->left ? -info->width : info->width),
                      buffer);

       /* Clean up and return. */
       free (buffer);
       return len;
     }


     int
     print_widget_arginfo (const struct printf_info *info, size_t n,
                           int *argtypes)
     {
       /* We always take exactly one argument and this is a pointer to the
          structure.. */
       if (n > 0)
         argtypes[0] = PA_POINTER;
       return 1;
     }


     int
     main (void)
     {
       /* Make a widget to print. */
       Widget mywidget;
       mywidget.name = "mywidget";

       /* Register the print function for widgets. */
       register_printf_function ('W', print_widget, print_widget_arginfo);

       /* Now print the widget. */
       printf ("|%W|\n", &mywidget);
       printf ("|%35W|\n", &mywidget);
       printf ("|%-35W|\n", &mywidget);

       return 0;
     }

   The output produced by this program looks like:

     |<Widget 0xffeffb7c: mywidget>|
     |      <Widget 0xffeffb7c: mywidget>|
     |<Widget 0xffeffb7c: mywidget>      |


File: libc.info,  Node: Predefined Printf Handlers,  Prev: Printf Extension Example,  Up: Customizing Printf

12.13.5 Predefined ‘printf’ Handlers
------------------------------------

The GNU C Library also contains a concrete and useful application of the
‘printf’ handler extension.  There are two functions available which
implement a special way to print floating-point numbers.

 -- Function: int printf_size (FILE *FP, const struct printf_info *INFO,
          const void *const *ARGS)

     Preliminary: | MT-Safe race:fp locale | AS-Unsafe corrupt heap |
     AC-Unsafe mem corrupt | *Note POSIX Safety Concepts::.

     Print a given floating point number as for the format ‘%f’ except
     that there is a postfix character indicating the divisor for the
     number to make this less than 1000.  There are two possible
     divisors: powers of 1024 or powers of 1000.  Which one is used
     depends on the format character specified while registered this
     handler.  If the character is of lower case, 1024 is used.  For
     upper case characters, 1000 is used.

     The postfix tag corresponds to bytes, kilobytes, megabytes,
     gigabytes, etc.  The full table is:

     low   Multiplier    From    Upper   Multiplier
     ’ ’   1                     ’ ’     1
     k     2^10 (1024)   kilo    K       10^3 (1000)
     m     2^20          mega    M       10^6
     g     2^30          giga    G       10^9
     t     2^40          tera    T       10^12
     p     2^50          peta    P       10^15
     e     2^60          exa     E       10^18
     z     2^70          zetta   Z       10^21
     y     2^80          yotta   Y       10^24

     The default precision is 3, i.e., 1024 is printed with a lower-case
     format character as if it were ‘%.3fk’ and will yield ‘1.000k’.

   Due to the requirements of ‘register_printf_function’ we must also
provide the function which returns information about the arguments.

 -- Function: int printf_size_info (const struct printf_info *INFO,
          size_t N, int *ARGTYPES)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function will return in ARGTYPES the information about the
     used parameters in the way the ‘vfprintf’ implementation expects
     it.  The format always takes one argument.

   To use these functions both functions must be registered with a call
like

     register_printf_function ('B', printf_size, printf_size_info);

   Here we register the functions to print numbers as powers of 1000
since the format character ‘'B'’ is an upper-case character.  If we
would additionally use ‘'b'’ in a line like

     register_printf_function ('b', printf_size, printf_size_info);

we could also print using a power of 1024.  Please note that all that is
different in these two lines is the format specifier.  The ‘printf_size’
function knows about the difference between lower and upper case format
specifiers.

   The use of ‘'B'’ and ‘'b'’ is no coincidence.  Rather it is the
preferred way to use this functionality since it is available on some
other systems which also use format specifiers.


File: libc.info,  Node: Formatted Input,  Next: EOF and Errors,  Prev: Customizing Printf,  Up: I/O on Streams

12.14 Formatted Input
=====================

The functions described in this section (‘scanf’ and related functions)
provide facilities for formatted input analogous to the formatted output
facilities.  These functions provide a mechanism for reading arbitrary
values under the control of a "format string" or "template string".

* Menu:

* Formatted Input Basics::      Some basics to get you started.
* Input Conversion Syntax::     Syntax of conversion specifications.
* Table of Input Conversions::  Summary of input conversions and what they do.
* Numeric Input Conversions::   Details of conversions for reading numbers.
* String Input Conversions::    Details of conversions for reading strings.
* Dynamic String Input::	String conversions that ‘malloc’ the buffer.
* Other Input Conversions::     Details of miscellaneous other conversions.
* Formatted Input Functions::   Descriptions of the actual functions.
* Variable Arguments Input::    ‘vscanf’ and friends.


File: libc.info,  Node: Formatted Input Basics,  Next: Input Conversion Syntax,  Up: Formatted Input

12.14.1 Formatted Input Basics
------------------------------

Calls to ‘scanf’ are superficially similar to calls to ‘printf’ in that
arbitrary arguments are read under the control of a template string.
While the syntax of the conversion specifications in the template is
very similar to that for ‘printf’, the interpretation of the template is
oriented more towards free-format input and simple pattern matching,
rather than fixed-field formatting.  For example, most ‘scanf’
conversions skip over any amount of “white space” (including spaces,
tabs, and newlines) in the input file, and there is no concept of
precision for the numeric input conversions as there is for the
corresponding output conversions.  Ordinarily, non-whitespace characters
in the template are expected to match characters in the input stream
exactly, but a matching failure is distinct from an input error on the
stream.

   Another area of difference between ‘scanf’ and ‘printf’ is that you
must remember to supply pointers rather than immediate values as the
optional arguments to ‘scanf’; the values that are read are stored in
the objects that the pointers point to.  Even experienced programmers
tend to forget this occasionally, so if your program is getting strange
errors that seem to be related to ‘scanf’, you might want to
double-check this.

   When a "matching failure" occurs, ‘scanf’ returns immediately,
leaving the first non-matching character as the next character to be
read from the stream.  The normal return value from ‘scanf’ is the
number of values that were assigned, so you can use this to determine if
a matching error happened before all the expected values were read.

   The ‘scanf’ function is typically used for things like reading in the
contents of tables.  For example, here is a function that uses ‘scanf’
to initialize an array of ‘double’:

     void
     readarray (double *array, int n)
     {
       int i;
       for (i=0; i<n; i++)
         if (scanf (" %lf", &(array[i])) != 1)
           invalid_input_error ();
     }

   The formatted input functions are not used as frequently as the
formatted output functions.  Partly, this is because it takes some care
to use them properly.  Another reason is that it is difficult to recover
from a matching error.

   If you are trying to read input that doesn’t match a single, fixed
pattern, you may be better off using a tool such as Flex to generate a
lexical scanner, or Bison to generate a parser, rather than using
‘scanf’.  For more information about these tools, see *note
(flex.info)Top::, and *note (bison.info)Top::.


File: libc.info,  Node: Input Conversion Syntax,  Next: Table of Input Conversions,  Prev: Formatted Input Basics,  Up: Formatted Input

12.14.2 Input Conversion Syntax
-------------------------------

A ‘scanf’ template string is a string that contains ordinary multibyte
characters interspersed with conversion specifications that start with
‘%’.

   Any whitespace character (as defined by the ‘isspace’ function; *note
Classification of Characters::) in the template causes any number of
whitespace characters in the input stream to be read and discarded.  The
whitespace characters that are matched need not be exactly the same
whitespace characters that appear in the template string.  For example,
write ‘ , ’ in the template to recognize a comma with optional
whitespace before and after.

   Other characters in the template string that are not part of
conversion specifications must match characters in the input stream
exactly; if this is not the case, a matching failure occurs.

   The conversion specifications in a ‘scanf’ template string have the
general form:

     % FLAGS WIDTH TYPE CONVERSION

   In more detail, an input conversion specification consists of an
initial ‘%’ character followed in sequence by:

   • An optional "flag character" ‘*’, which says to ignore the text
     read for this specification.  When ‘scanf’ finds a conversion
     specification that uses this flag, it reads input as directed by
     the rest of the conversion specification, but it discards this
     input, does not use a pointer argument, and does not increment the
     count of successful assignments.

   • An optional flag character ‘a’ (valid with string conversions only)
     which requests allocation of a buffer long enough to store the
     string in.  (This is a GNU extension.)  *Note Dynamic String
     Input::.

   • An optional decimal integer that specifies the "maximum field
     width".  Reading of characters from the input stream stops either
     when this maximum is reached or when a non-matching character is
     found, whichever happens first.  Most conversions discard initial
     whitespace characters (those that don’t are explicitly documented),
     and these discarded characters don’t count towards the maximum
     field width.  String input conversions store a null character to
     mark the end of the input; the maximum field width does not include
     this terminator.

   • An optional "type modifier character".  For example, you can
     specify a type modifier of ‘l’ with integer conversions such as
     ‘%d’ to specify that the argument is a pointer to a ‘long int’
     rather than a pointer to an ‘int’.

   • A character that specifies the conversion to be applied.

   The exact options that are permitted and how they are interpreted
vary between the different conversion specifiers.  See the descriptions
of the individual conversions for information about the particular
options that they allow.

   With the ‘-Wformat’ option, the GNU C compiler checks calls to
‘scanf’ and related functions.  It examines the format string and
verifies that the correct number and types of arguments are supplied.
There is also a GNU C syntax to tell the compiler that a function you
write uses a ‘scanf’-style format string.  *Note Declaring Attributes of
Functions: (gcc)Function Attributes, for more information.


File: libc.info,  Node: Table of Input Conversions,  Next: Numeric Input Conversions,  Prev: Input Conversion Syntax,  Up: Formatted Input

12.14.3 Table of Input Conversions
----------------------------------

Here is a table that summarizes the various conversion specifications:

‘%d’
     Matches an optionally signed integer written in decimal.  *Note
     Numeric Input Conversions::.

‘%i’
     Matches an optionally signed integer in any of the formats that the
     C language defines for specifying an integer constant.  *Note
     Numeric Input Conversions::.

‘%o’
     Matches an unsigned integer written in octal radix.  *Note Numeric
     Input Conversions::.

‘%u’
     Matches an unsigned integer written in decimal radix.  *Note
     Numeric Input Conversions::.

‘%x’, ‘%X’
     Matches an unsigned integer written in hexadecimal radix.  *Note
     Numeric Input Conversions::.

‘%e’, ‘%f’, ‘%g’, ‘%E’, ‘%G’
     Matches an optionally signed floating-point number.  *Note Numeric
     Input Conversions::.

‘%s’

     Matches a string containing only non-whitespace characters.  *Note
     String Input Conversions::.  The presence of the ‘l’ modifier
     determines whether the output is stored as a wide character string
     or a multibyte string.  If ‘%s’ is used in a wide character
     function the string is converted as with multiple calls to
     ‘wcrtomb’ into a multibyte string.  This means that the buffer must
     provide room for ‘MB_CUR_MAX’ bytes for each wide character read.
     In case ‘%ls’ is used in a multibyte function the result is
     converted into wide characters as with multiple calls of ‘mbrtowc’
     before being stored in the user provided buffer.

‘%S’
     This is an alias for ‘%ls’ which is supported for compatibility
     with the Unix standard.

‘%[’
     Matches a string of characters that belong to a specified set.
     *Note String Input Conversions::.  The presence of the ‘l’ modifier
     determines whether the output is stored as a wide character string
     or a multibyte string.  If ‘%[’ is used in a wide character
     function the string is converted as with multiple calls to
     ‘wcrtomb’ into a multibyte string.  This means that the buffer must
     provide room for ‘MB_CUR_MAX’ bytes for each wide character read.
     In case ‘%l[’ is used in a multibyte function the result is
     converted into wide characters as with multiple calls of ‘mbrtowc’
     before being stored in the user provided buffer.

‘%c’
     Matches a string of one or more characters; the number of
     characters read is controlled by the maximum field width given for
     the conversion.  *Note String Input Conversions::.

     If ‘%c’ is used in a wide stream function the read value is
     converted from a wide character to the corresponding multibyte
     character before storing it.  Note that this conversion can produce
     more than one byte of output and therefore the provided buffer must
     be large enough for up to ‘MB_CUR_MAX’ bytes for each character.
     If ‘%lc’ is used in a multibyte function the input is treated as a
     multibyte sequence (and not bytes) and the result is converted as
     with calls to ‘mbrtowc’.

‘%C’
     This is an alias for ‘%lc’ which is supported for compatibility
     with the Unix standard.

‘%p’
     Matches a pointer value in the same implementation-defined format
     used by the ‘%p’ output conversion for ‘printf’.  *Note Other Input
     Conversions::.

‘%n’
     This conversion doesn’t read any characters; it records the number
     of characters read so far by this call.  *Note Other Input
     Conversions::.

‘%%’
     This matches a literal ‘%’ character in the input stream.  No
     corresponding argument is used.  *Note Other Input Conversions::.

   If the syntax of a conversion specification is invalid, the behavior
is undefined.  If there aren’t enough function arguments provided to
supply addresses for all the conversion specifications in the template
strings that perform assignments, or if the arguments are not of the
correct types, the behavior is also undefined.  On the other hand, extra
arguments are simply ignored.


File: libc.info,  Node: Numeric Input Conversions,  Next: String Input Conversions,  Prev: Table of Input Conversions,  Up: Formatted Input

12.14.4 Numeric Input Conversions
---------------------------------

This section describes the ‘scanf’ conversions for reading numeric
values.

   The ‘%d’ conversion matches an optionally signed integer in decimal
radix.  The syntax that is recognized is the same as that for the
‘strtol’ function (*note Parsing of Integers::) with the value ‘10’ for
the BASE argument.

   The ‘%i’ conversion matches an optionally signed integer in any of
the formats that the C language defines for specifying an integer
constant.  The syntax that is recognized is the same as that for the
‘strtol’ function (*note Parsing of Integers::) with the value ‘0’ for
the BASE argument.  (You can print integers in this syntax with ‘printf’
by using the ‘#’ flag character with the ‘%x’, ‘%o’, or ‘%d’ conversion.
*Note Integer Conversions::.)

   For example, any of the strings ‘10’, ‘0xa’, or ‘012’ could be read
in as integers under the ‘%i’ conversion.  Each of these specifies a
number with decimal value ‘10’.

   The ‘%o’, ‘%u’, and ‘%x’ conversions match unsigned integers in
octal, decimal, and hexadecimal radices, respectively.  The syntax that
is recognized is the same as that for the ‘strtoul’ function (*note
Parsing of Integers::) with the appropriate value (‘8’, ‘10’, or ‘16’)
for the BASE argument.

   The ‘%X’ conversion is identical to the ‘%x’ conversion.  They both
permit either uppercase or lowercase letters to be used as digits.

   The default type of the corresponding argument for the ‘%d’ and ‘%i’
conversions is ‘int *’, and ‘unsigned int *’ for the other integer
conversions.  You can use the following type modifiers to specify other
sizes of integer:

‘hh’
     Specifies that the argument is a ‘signed char *’ or ‘unsigned char
     *’.

     This modifier was introduced in ISO C99.

‘h’
     Specifies that the argument is a ‘short int *’ or ‘unsigned short
     int *’.

‘j’
     Specifies that the argument is a ‘intmax_t *’ or ‘uintmax_t *’.

     This modifier was introduced in ISO C99.

‘l’
     Specifies that the argument is a ‘long int *’ or ‘unsigned long int
     *’.  Two ‘l’ characters is like the ‘L’ modifier, below.

     If used with ‘%c’ or ‘%s’ the corresponding parameter is considered
     as a pointer to a wide character or wide character string
     respectively.  This use of ‘l’ was introduced in Amendment 1 to
     ISO C90.

‘ll’
‘L’
‘q’
     Specifies that the argument is a ‘long long int *’ or ‘unsigned
     long long int *’.  (The ‘long long’ type is an extension supported
     by the GNU C compiler.  For systems that don’t provide extra-long
     integers, this is the same as ‘long int’.)

     The ‘q’ modifier is another name for the same thing, which comes
     from 4.4 BSD; a ‘long long int’ is sometimes called a “quad” ‘int’.

‘t’
     Specifies that the argument is a ‘ptrdiff_t *’.

     This modifier was introduced in ISO C99.

‘z’
     Specifies that the argument is a ‘size_t *’.

     This modifier was introduced in ISO C99.

   All of the ‘%e’, ‘%f’, ‘%g’, ‘%E’, and ‘%G’ input conversions are
interchangeable.  They all match an optionally signed floating point
number, in the same syntax as for the ‘strtod’ function (*note Parsing
of Floats::).

   For the floating-point input conversions, the default argument type
is ‘float *’.  (This is different from the corresponding output
conversions, where the default type is ‘double’; remember that ‘float’
arguments to ‘printf’ are converted to ‘double’ by the default argument
promotions, but ‘float *’ arguments are not promoted to ‘double *’.)
You can specify other sizes of float using these type modifiers:

‘l’
     Specifies that the argument is of type ‘double *’.

‘L’
     Specifies that the argument is of type ‘long double *’.

   For all the above number parsing formats there is an additional
optional flag ‘'’.  When this flag is given the ‘scanf’ function expects
the number represented in the input string to be formatted according to
the grouping rules of the currently selected locale (*note General
Numeric::).

   If the ‘"C"’ or ‘"POSIX"’ locale is selected there is no difference.
But for a locale which specifies values for the appropriate fields in
the locale the input must have the correct form in the input.  Otherwise
the longest prefix with a correct form is processed.


File: libc.info,  Node: String Input Conversions,  Next: Dynamic String Input,  Prev: Numeric Input Conversions,  Up: Formatted Input

12.14.5 String Input Conversions
--------------------------------

This section describes the ‘scanf’ input conversions for reading string
and character values: ‘%s’, ‘%S’, ‘%[’, ‘%c’, and ‘%C’.

   You have two options for how to receive the input from these
conversions:

   • Provide a buffer to store it in.  This is the default.  You should
     provide an argument of type ‘char *’ or ‘wchar_t *’ (the latter if
     the ‘l’ modifier is present).

     *Warning:* To make a robust program, you must make sure that the
     input (plus its terminating null) cannot possibly exceed the size
     of the buffer you provide.  In general, the only way to do this is
     to specify a maximum field width one less than the buffer size.
     *If you provide the buffer, always specify a maximum field width to
     prevent overflow.*

   • Ask ‘scanf’ to allocate a big enough buffer, by specifying the ‘a’
     flag character.  This is a GNU extension.  You should provide an
     argument of type ‘char **’ for the buffer address to be stored in.
     *Note Dynamic String Input::.

   The ‘%c’ conversion is the simplest: it matches a fixed number of
characters, always.  The maximum field width says how many characters to
read; if you don’t specify the maximum, the default is 1.  This
conversion doesn’t append a null character to the end of the text it
reads.  It also does not skip over initial whitespace characters.  It
reads precisely the next N characters, and fails if it cannot get that
many.  Since there is always a maximum field width with ‘%c’ (whether
specified, or 1 by default), you can always prevent overflow by making
the buffer long enough.

   If the format is ‘%lc’ or ‘%C’ the function stores wide characters
which are converted using the conversion determined at the time the
stream was opened from the external byte stream.  The number of bytes
read from the medium is limited by ‘MB_CUR_LEN * N’ but at most N wide
characters get stored in the output string.

   The ‘%s’ conversion matches a string of non-whitespace characters.
It skips and discards initial whitespace, but stops when it encounters
more whitespace after having read something.  It stores a null character
at the end of the text that it reads.

   For example, reading the input:

      hello, world

with the conversion ‘%10c’ produces ‘" hello, wo"’, but reading the same
input with the conversion ‘%10s’ produces ‘"hello,"’.

   *Warning:* If you do not specify a field width for ‘%s’, then the
number of characters read is limited only by where the next whitespace
character appears.  This almost certainly means that invalid input can
make your program crash—which is a bug.

   The ‘%ls’ and ‘%S’ format are handled just like ‘%s’ except that the
external byte sequence is converted using the conversion associated with
the stream to wide characters with their own encoding.  A width or
precision specified with the format do not directly determine how many
bytes are read from the stream since they measure wide characters.  But
an upper limit can be computed by multiplying the value of the width or
precision by ‘MB_CUR_MAX’.

   To read in characters that belong to an arbitrary set of your choice,
use the ‘%[’ conversion.  You specify the set between the ‘[’ character
and a following ‘]’ character, using the same syntax used in regular
expressions for explicit sets of characters.  As special cases:

   • A literal ‘]’ character can be specified as the first character of
     the set.

   • An embedded ‘-’ character (that is, one that is not the first or
     last character of the set) is used to specify a range of
     characters.

   • If a caret character ‘^’ immediately follows the initial ‘[’, then
     the set of allowed input characters is everything _except_ the
     characters listed.

   The ‘%[’ conversion does not skip over initial whitespace characters.

   Note that the "character class" syntax available in character sets
that appear inside regular expressions (such as ‘[:alpha:]’) is _not_
available in the ‘%[’ conversion.

   Here are some examples of ‘%[’ conversions and what they mean:

‘%25[1234567890]’
     Matches a string of up to 25 digits.

‘%25[][]’
     Matches a string of up to 25 square brackets.

‘%25[^ \f\n\r\t\v]’
     Matches a string up to 25 characters long that doesn’t contain any
     of the standard whitespace characters.  This is slightly different
     from ‘%s’, because if the input begins with a whitespace character,
     ‘%[’ reports a matching failure while ‘%s’ simply discards the
     initial whitespace.

‘%25[a-z]’
     Matches up to 25 lowercase characters.

   As for ‘%c’ and ‘%s’ the ‘%[’ format is also modified to produce wide
characters if the ‘l’ modifier is present.  All what is said about ‘%ls’
above is true for ‘%l[’.

   One more reminder: the ‘%s’ and ‘%[’ conversions are *dangerous* if
you don’t specify a maximum width or use the ‘a’ flag, because input too
long would overflow whatever buffer you have provided for it.  No matter
how long your buffer is, a user could supply input that is longer.  A
well-written program reports invalid input with a comprehensible error
message, not with a crash.


File: libc.info,  Node: Dynamic String Input,  Next: Other Input Conversions,  Prev: String Input Conversions,  Up: Formatted Input

12.14.6 Dynamically Allocating String Conversions
-------------------------------------------------

A GNU extension to formatted input lets you safely read a string with no
maximum size.  Using this feature, you don’t supply a buffer; instead,
‘scanf’ allocates a buffer big enough to hold the data and gives you its
address.  To use this feature, write ‘a’ as a flag character, as in
‘%as’ or ‘%a[0-9a-z]’.

   The pointer argument you supply for where to store the input should
have type ‘char **’.  The ‘scanf’ function allocates a buffer and stores
its address in the word that the argument points to.  You should free
the buffer with ‘free’ when you no longer need it.

   Here is an example of using the ‘a’ flag with the ‘%[…]’ conversion
specification to read a “variable assignment” of the form ‘VARIABLE =
VALUE’.

     {
       char *variable, *value;

       if (2 > scanf ("%a[a-zA-Z0-9] = %a[^\n]\n",
     		 &variable, &value))
         {
           invalid_input_error ();
           return 0;
         }

       …
     }


File: libc.info,  Node: Other Input Conversions,  Next: Formatted Input Functions,  Prev: Dynamic String Input,  Up: Formatted Input

12.14.7 Other Input Conversions
-------------------------------

This section describes the miscellaneous input conversions.

   The ‘%p’ conversion is used to read a pointer value.  It recognizes
the same syntax used by the ‘%p’ output conversion for ‘printf’ (*note
Other Output Conversions::); that is, a hexadecimal number just as the
‘%x’ conversion accepts.  The corresponding argument should be of type
‘void **’; that is, the address of a place to store a pointer.

   The resulting pointer value is not guaranteed to be valid if it was
not originally written during the same program execution that reads it
in.

   The ‘%n’ conversion produces the number of characters read so far by
this call.  The corresponding argument should be of type ‘int *’.  This
conversion works in the same way as the ‘%n’ conversion for ‘printf’;
see *note Other Output Conversions::, for an example.

   The ‘%n’ conversion is the only mechanism for determining the success
of literal matches or conversions with suppressed assignments.  If the
‘%n’ follows the locus of a matching failure, then no value is stored
for it since ‘scanf’ returns before processing the ‘%n’.  If you store
‘-1’ in that argument slot before calling ‘scanf’, the presence of ‘-1’
after ‘scanf’ indicates an error occurred before the ‘%n’ was reached.

   Finally, the ‘%%’ conversion matches a literal ‘%’ character in the
input stream, without using an argument.  This conversion does not
permit any flags, field width, or type modifier to be specified.


File: libc.info,  Node: Formatted Input Functions,  Next: Variable Arguments Input,  Prev: Other Input Conversions,  Up: Formatted Input

12.14.8 Formatted Input Functions
---------------------------------

Here are the descriptions of the functions for performing formatted
input.  Prototypes for these functions are in the header file ‘stdio.h’.

 -- Function: int scanf (const char *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     The ‘scanf’ function reads formatted input from the stream ‘stdin’
     under the control of the template string TEMPLATE.  The optional
     arguments are pointers to the places which receive the resulting
     values.

     The return value is normally the number of successful assignments.
     If an end-of-file condition is detected before any matches are
     performed, including matches against whitespace and literal
     characters in the template, then ‘EOF’ is returned.

 -- Function: int wscanf (const wchar_t *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     The ‘wscanf’ function reads formatted input from the stream ‘stdin’
     under the control of the template string TEMPLATE.  The optional
     arguments are pointers to the places which receive the resulting
     values.

     The return value is normally the number of successful assignments.
     If an end-of-file condition is detected before any matches are
     performed, including matches against whitespace and literal
     characters in the template, then ‘WEOF’ is returned.

 -- Function: int fscanf (FILE *STREAM, const char *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is just like ‘scanf’, except that the input is read
     from the stream STREAM instead of ‘stdin’.

 -- Function: int fwscanf (FILE *STREAM, const wchar_t *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is just like ‘wscanf’, except that the input is read
     from the stream STREAM instead of ‘stdin’.

 -- Function: int sscanf (const char *S, const char *TEMPLATE, …)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is like ‘scanf’, except that the characters are taken from the
     null-terminated string S instead of from a stream.  Reaching the
     end of the string is treated as an end-of-file condition.

     The behavior of this function is undefined if copying takes place
     between objects that overlap—for example, if S is also given as an
     argument to receive a string read under control of the ‘%s’, ‘%S’,
     or ‘%[’ conversion.

 -- Function: int swscanf (const wchar_t *WS, const wchar_t *TEMPLATE,
          …)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is like ‘wscanf’, except that the characters are taken from
     the null-terminated string WS instead of from a stream.  Reaching
     the end of the string is treated as an end-of-file condition.

     The behavior of this function is undefined if copying takes place
     between objects that overlap—for example, if WS is also given as an
     argument to receive a string read under control of the ‘%s’, ‘%S’,
     or ‘%[’ conversion.


File: libc.info,  Node: Variable Arguments Input,  Prev: Formatted Input Functions,  Up: Formatted Input

12.14.9 Variable Arguments Input Functions
------------------------------------------

The functions ‘vscanf’ and friends are provided so that you can define
your own variadic ‘scanf’-like functions that make use of the same
internals as the built-in formatted output functions.  These functions
are analogous to the ‘vprintf’ series of output functions.  *Note
Variable Arguments Output::, for important information on how to use
them.

   *Portability Note:* The functions listed in this section were
introduced in ISO C99 and were before available as GNU extensions.

 -- Function: int vscanf (const char *TEMPLATE, va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is similar to ‘scanf’, but instead of taking a
     variable number of arguments directly, it takes an argument list
     pointer AP of type ‘va_list’ (*note Variadic Functions::).

 -- Function: int vwscanf (const wchar_t *TEMPLATE, va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This function is similar to ‘wscanf’, but instead of taking a
     variable number of arguments directly, it takes an argument list
     pointer AP of type ‘va_list’ (*note Variadic Functions::).

 -- Function: int vfscanf (FILE *STREAM, const char *TEMPLATE, va_list
          AP)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This is the equivalent of ‘fscanf’ with the variable argument list
     specified directly as for ‘vscanf’.

 -- Function: int vfwscanf (FILE *STREAM, const wchar_t *TEMPLATE,
          va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe corrupt heap | AC-Unsafe
     mem lock corrupt | *Note POSIX Safety Concepts::.

     This is the equivalent of ‘fwscanf’ with the variable argument list
     specified directly as for ‘vwscanf’.

 -- Function: int vsscanf (const char *S, const char *TEMPLATE, va_list
          AP)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is the equivalent of ‘sscanf’ with the variable argument list
     specified directly as for ‘vscanf’.

 -- Function: int vswscanf (const wchar_t *S, const wchar_t *TEMPLATE,
          va_list AP)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     This is the equivalent of ‘swscanf’ with the variable argument list
     specified directly as for ‘vwscanf’.

   In GNU C, there is a special construct you can use to let the
compiler know that a function uses a ‘scanf’-style format string.  Then
it can check the number and types of arguments in each call to the
function, and warn you when they do not match the format string.  For
details, see *note Declaring Attributes of Functions: (gcc)Function
Attributes.


File: libc.info,  Node: EOF and Errors,  Next: Error Recovery,  Prev: Formatted Input,  Up: I/O on Streams

12.15 End-Of-File and Errors
============================

Many of the functions described in this chapter return the value of the
macro ‘EOF’ to indicate unsuccessful completion of the operation.  Since
‘EOF’ is used to report both end of file and random errors, it’s often
better to use the ‘feof’ function to check explicitly for end of file
and ‘ferror’ to check for errors.  These functions check indicators that
are part of the internal state of the stream object, indicators set if
the appropriate condition was detected by a previous I/O operation on
that stream.

 -- Macro: int EOF

     This macro is an integer value that is returned by a number of
     narrow stream functions to indicate an end-of-file condition, or
     some other error situation.  With the GNU C Library, ‘EOF’ is ‘-1’.
     In other libraries, its value may be some other negative number.

     This symbol is declared in ‘stdio.h’.

 -- Macro: int WEOF

     This macro is an integer value that is returned by a number of wide
     stream functions to indicate an end-of-file condition, or some
     other error situation.  With the GNU C Library, ‘WEOF’ is ‘-1’.  In
     other libraries, its value may be some other negative number.

     This symbol is declared in ‘wchar.h’.

 -- Function: int feof (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Safe | AC-Unsafe lock | *Note POSIX
     Safety Concepts::.

     The ‘feof’ function returns nonzero if and only if the end-of-file
     indicator for the stream STREAM is set.

     This symbol is declared in ‘stdio.h’.

 -- Function: int feof_unlocked (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘feof_unlocked’ function is equivalent to the ‘feof’ function
     except that it does not implicitly lock the stream.

     This function is a GNU extension.

     This symbol is declared in ‘stdio.h’.

 -- Function: int ferror (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Safe | AC-Unsafe lock | *Note POSIX
     Safety Concepts::.

     The ‘ferror’ function returns nonzero if and only if the error
     indicator for the stream STREAM is set, indicating that an error
     has occurred on a previous operation on the stream.

     This symbol is declared in ‘stdio.h’.

 -- Function: int ferror_unlocked (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘ferror_unlocked’ function is equivalent to the ‘ferror’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.

     This symbol is declared in ‘stdio.h’.

   In addition to setting the error indicator associated with the
stream, the functions that operate on streams also set ‘errno’ in the
same way as the corresponding low-level functions that operate on file
descriptors.  For example, all of the functions that perform output to a
stream—such as ‘fputc’, ‘printf’, and ‘fflush’—are implemented in terms
of ‘write’, and all of the ‘errno’ error conditions defined for ‘write’
are meaningful for these functions.  For more information about the
descriptor-level I/O functions, see *note Low-Level I/O::.


File: libc.info,  Node: Error Recovery,  Next: Binary Streams,  Prev: EOF and Errors,  Up: I/O on Streams

12.16 Recovering from errors
============================

You may explicitly clear the error and EOF flags with the ‘clearerr’
function.

 -- Function: void clearerr (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Safe | AC-Unsafe lock | *Note POSIX
     Safety Concepts::.

     This function clears the end-of-file and error indicators for the
     stream STREAM.

     The file positioning functions (*note File Positioning::) also
     clear the end-of-file indicator for the stream.

 -- Function: void clearerr_unlocked (FILE *STREAM)

     Preliminary: | MT-Safe race:stream | AS-Safe | AC-Safe | *Note
     POSIX Safety Concepts::.

     The ‘clearerr_unlocked’ function is equivalent to the ‘clearerr’
     function except that it does not implicitly lock the stream.

     This function is a GNU extension.

   Note that it is _not_ correct to just clear the error flag and retry
a failed stream operation.  After a failed write, any number of
characters since the last buffer flush may have been committed to the
file, while some buffered data may have been discarded.  Merely retrying
can thus cause lost or repeated data.

   A failed read may leave the file pointer in an inappropriate position
for a second try.  In both cases, you should seek to a known position
before retrying.

   Most errors that can happen are not recoverable — a second try will
always fail again in the same way.  So usually it is best to give up and
report the error to the user, rather than install complicated recovery
logic.

   One important exception is ‘EINTR’ (*note Interrupted Primitives::).
Many stream I/O implementations will treat it as an ordinary error,
which can be quite inconvenient.  You can avoid this hassle by
installing all signals with the ‘SA_RESTART’ flag.

   For similar reasons, setting nonblocking I/O on a stream’s file
descriptor is not usually advisable.


File: libc.info,  Node: Binary Streams,  Next: File Positioning,  Prev: Error Recovery,  Up: I/O on Streams

12.17 Text and Binary Streams
=============================

GNU systems and other POSIX-compatible operating systems organize all
files as uniform sequences of characters.  However, some other systems
make a distinction between files containing text and files containing
binary data, and the input and output facilities of ISO C provide for
this distinction.  This section tells you how to write programs portable
to such systems.

   When you open a stream, you can specify either a "text stream" or a
"binary stream".  You indicate that you want a binary stream by
specifying the ‘b’ modifier in the OPENTYPE argument to ‘fopen’; see
*note Opening Streams::.  Without this option, ‘fopen’ opens the file as
a text stream.

   Text and binary streams differ in several ways:

   • The data read from a text stream is divided into "lines" which are
     terminated by newline (‘'\n'’) characters, while a binary stream is
     simply a long series of characters.  A text stream might on some
     systems fail to handle lines more than 254 characters long
     (including the terminating newline character).

   • On some systems, text files can contain only printing characters,
     horizontal tab characters, and newlines, and so text streams may
     not support other characters.  However, binary streams can handle
     any character value.

   • Space characters that are written immediately preceding a newline
     character in a text stream may disappear when the file is read in
     again.

   • More generally, there need not be a one-to-one mapping between
     characters that are read from or written to a text stream, and the
     characters in the actual file.

   Since a binary stream is always more capable and more predictable
than a text stream, you might wonder what purpose text streams serve.
Why not simply always use binary streams?  The answer is that on these
operating systems, text and binary streams use different file formats,
and the only way to read or write “an ordinary file of text” that can
work with other text-oriented programs is through a text stream.

   In the GNU C Library, and on all POSIX systems, there is no
difference between text streams and binary streams.  When you open a
stream, you get the same kind of stream regardless of whether you ask
for binary.  This stream can handle any file content, and has none of
the restrictions that text streams sometimes have.


File: libc.info,  Node: File Positioning,  Next: Portable Positioning,  Prev: Binary Streams,  Up: I/O on Streams

12.18 File Positioning
======================

The "file position" of a stream describes where in the file the stream
is currently reading or writing.  I/O on the stream advances the file
position through the file.  On GNU systems, the file position is
represented as an integer, which counts the number of bytes from the
beginning of the file.  *Note File Position::.

   During I/O to an ordinary disk file, you can change the file position
whenever you wish, so as to read or write any portion of the file.  Some
other kinds of files may also permit this.  Files which support changing
the file position are sometimes referred to as "random-access" files.

   You can use the functions in this section to examine or modify the
file position indicator associated with a stream.  The symbols listed
below are declared in the header file ‘stdio.h’.

 -- Function: long int ftell (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function returns the current file position of the stream
     STREAM.

     This function can fail if the stream doesn’t support file
     positioning, or if the file position can’t be represented in a
     ‘long int’, and possibly for other reasons as well.  If a failure
     occurs, a value of ‘-1’ is returned.

 -- Function: off_t ftello (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘ftello’ function is similar to ‘ftell’, except that it returns
     a value of type ‘off_t’.  Systems which support this type use it to
     describe all file positions, unlike the POSIX specification which
     uses a long int.  The two are not necessarily the same size.
     Therefore, using ftell can lead to problems if the implementation
     is written on top of a POSIX compliant low-level I/O
     implementation, and using ‘ftello’ is preferable whenever it is
     available.

     If this function fails it returns ‘(off_t) -1’.  This can happen
     due to missing support for file positioning or internal errors.
     Otherwise the return value is the current file position.

     The function is an extension defined in the Unix Single
     Specification version 2.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32 bit system this function is in fact ‘ftello64’.  I.e., the LFS
     interface transparently replaces the old interface.

 -- Function: off64_t ftello64 (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function is similar to ‘ftello’ with the only difference that
     the return value is of type ‘off64_t’.  This also requires that the
     stream STREAM was opened using either ‘fopen64’, ‘freopen64’, or
     ‘tmpfile64’ since otherwise the underlying file operations to
     position the file pointer beyond the 2^31 bytes limit might fail.

     If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32
     bits machine this function is available under the name ‘ftello’ and
     so transparently replaces the old interface.

 -- Function: int fseek (FILE *STREAM, long int OFFSET, int WHENCE)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘fseek’ function is used to change the file position of the
     stream STREAM.  The value of WHENCE must be one of the constants
     ‘SEEK_SET’, ‘SEEK_CUR’, or ‘SEEK_END’, to indicate whether the
     OFFSET is relative to the beginning of the file, the current file
     position, or the end of the file, respectively.

     This function returns a value of zero if the operation was
     successful, and a nonzero value to indicate failure.  A successful
     call also clears the end-of-file indicator of STREAM and discards
     any characters that were “pushed back” by the use of ‘ungetc’.

     ‘fseek’ either flushes any buffered output before setting the file
     position or else remembers it so it will be written later in its
     proper place in the file.

 -- Function: int fseeko (FILE *STREAM, off_t OFFSET, int WHENCE)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function is similar to ‘fseek’ but it corrects a problem with
     ‘fseek’ in a system with POSIX types.  Using a value of type ‘long
     int’ for the offset is not compatible with POSIX. ‘fseeko’ uses the
     correct type ‘off_t’ for the OFFSET parameter.

     For this reason it is a good idea to prefer ‘ftello’ whenever it is
     available since its functionality is (if different at all) closer
     the underlying definition.

     The functionality and return value are the same as for ‘fseek’.

     The function is an extension defined in the Unix Single
     Specification version 2.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32 bit system this function is in fact ‘fseeko64’.  I.e., the LFS
     interface transparently replaces the old interface.

 -- Function: int fseeko64 (FILE *STREAM, off64_t OFFSET, int WHENCE)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function is similar to ‘fseeko’ with the only difference that
     the OFFSET parameter is of type ‘off64_t’.  This also requires that
     the stream STREAM was opened using either ‘fopen64’, ‘freopen64’,
     or ‘tmpfile64’ since otherwise the underlying file operations to
     position the file pointer beyond the 2^31 bytes limit might fail.

     If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32
     bits machine this function is available under the name ‘fseeko’ and
     so transparently replaces the old interface.

   *Portability Note:* In non-POSIX systems, ‘ftell’, ‘ftello’, ‘fseek’
and ‘fseeko’ might work reliably only on binary streams.  *Note Binary
Streams::.

   The following symbolic constants are defined for use as the WHENCE
argument to ‘fseek’.  They are also used with the ‘lseek’ function
(*note I/O Primitives::) and to specify offsets for file locks (*note
Control Operations::).

 -- Macro: int SEEK_SET

     This is an integer constant which, when used as the WHENCE argument
     to the ‘fseek’ or ‘fseeko’ functions, specifies that the offset
     provided is relative to the beginning of the file.

 -- Macro: int SEEK_CUR

     This is an integer constant which, when used as the WHENCE argument
     to the ‘fseek’ or ‘fseeko’ functions, specifies that the offset
     provided is relative to the current file position.

 -- Macro: int SEEK_END

     This is an integer constant which, when used as the WHENCE argument
     to the ‘fseek’ or ‘fseeko’ functions, specifies that the offset
     provided is relative to the end of the file.

 -- Function: void rewind (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘rewind’ function positions the stream STREAM at the beginning
     of the file.  It is equivalent to calling ‘fseek’ or ‘fseeko’ on
     the STREAM with an OFFSET argument of ‘0L’ and a WHENCE argument of
     ‘SEEK_SET’, except that the return value is discarded and the error
     indicator for the stream is reset.

   These three aliases for the ‘SEEK_…’ constants exist for the sake of
compatibility with older BSD systems.  They are defined in two different
header files: ‘fcntl.h’ and ‘sys/file.h’.

‘L_SET’

     An alias for ‘SEEK_SET’.

‘L_INCR’

     An alias for ‘SEEK_CUR’.

‘L_XTND’

     An alias for ‘SEEK_END’.


File: libc.info,  Node: Portable Positioning,  Next: Stream Buffering,  Prev: File Positioning,  Up: I/O on Streams

12.19 Portable File-Position Functions
======================================

On GNU systems, the file position is truly a character count.  You can
specify any character count value as an argument to ‘fseek’ or ‘fseeko’
and get reliable results for any random access file.  However, some ISO C
systems do not represent file positions in this way.

   On some systems where text streams truly differ from binary streams,
it is impossible to represent the file position of a text stream as a
count of characters from the beginning of the file.  For example, the
file position on some systems must encode both a record offset within
the file, and a character offset within the record.

   As a consequence, if you want your programs to be portable to these
systems, you must observe certain rules:

   • The value returned from ‘ftell’ on a text stream has no predictable
     relationship to the number of characters you have read so far.  The
     only thing you can rely on is that you can use it subsequently as
     the OFFSET argument to ‘fseek’ or ‘fseeko’ to move back to the same
     file position.

   • In a call to ‘fseek’ or ‘fseeko’ on a text stream, either the
     OFFSET must be zero, or WHENCE must be ‘SEEK_SET’ and the OFFSET
     must be the result of an earlier call to ‘ftell’ on the same
     stream.

   • The value of the file position indicator of a text stream is
     undefined while there are characters that have been pushed back
     with ‘ungetc’ that haven’t been read or discarded.  *Note
     Unreading::.

   But even if you observe these rules, you may still have trouble for
long files, because ‘ftell’ and ‘fseek’ use a ‘long int’ value to
represent the file position.  This type may not have room to encode all
the file positions in a large file.  Using the ‘ftello’ and ‘fseeko’
functions might help here since the ‘off_t’ type is expected to be able
to hold all file position values but this still does not help to handle
additional information which must be associated with a file position.

   So if you do want to support systems with peculiar encodings for the
file positions, it is better to use the functions ‘fgetpos’ and
‘fsetpos’ instead.  These functions represent the file position using
the data type ‘fpos_t’, whose internal representation varies from system
to system.

   These symbols are declared in the header file ‘stdio.h’.

 -- Data Type: fpos_t

     This is the type of an object that can encode information about the
     file position of a stream, for use by the functions ‘fgetpos’ and
     ‘fsetpos’.

     In the GNU C Library, ‘fpos_t’ is an opaque data structure that
     contains internal data to represent file offset and conversion
     state information.  In other systems, it might have a different
     internal representation.

     When compiling with ‘_FILE_OFFSET_BITS == 64’ on a 32 bit machine
     this type is in fact equivalent to ‘fpos64_t’ since the LFS
     interface transparently replaces the old interface.

 -- Data Type: fpos64_t

     This is the type of an object that can encode information about the
     file position of a stream, for use by the functions ‘fgetpos64’ and
     ‘fsetpos64’.

     In the GNU C Library, ‘fpos64_t’ is an opaque data structure that
     contains internal data to represent file offset and conversion
     state information.  In other systems, it might have a different
     internal representation.

 -- Function: int fgetpos (FILE *STREAM, fpos_t *POSITION)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function stores the value of the file position indicator for
     the stream STREAM in the ‘fpos_t’ object pointed to by POSITION.
     If successful, ‘fgetpos’ returns zero; otherwise it returns a
     nonzero value and stores an implementation-defined positive value
     in ‘errno’.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32 bit system the function is in fact ‘fgetpos64’.  I.e., the LFS
     interface transparently replaces the old interface.

 -- Function: int fgetpos64 (FILE *STREAM, fpos64_t *POSITION)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function is similar to ‘fgetpos’ but the file position is
     returned in a variable of type ‘fpos64_t’ to which POSITION points.

     If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32
     bits machine this function is available under the name ‘fgetpos’
     and so transparently replaces the old interface.

 -- Function: int fsetpos (FILE *STREAM, const fpos_t *POSITION)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function sets the file position indicator for the stream
     STREAM to the position POSITION, which must have been set by a
     previous call to ‘fgetpos’ on the same stream.  If successful,
     ‘fsetpos’ clears the end-of-file indicator on the stream, discards
     any characters that were “pushed back” by the use of ‘ungetc’, and
     returns a value of zero.  Otherwise, ‘fsetpos’ returns a nonzero
     value and stores an implementation-defined positive value in
     ‘errno’.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32 bit system the function is in fact ‘fsetpos64’.  I.e., the LFS
     interface transparently replaces the old interface.

 -- Function: int fsetpos64 (FILE *STREAM, const fpos64_t *POSITION)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function is similar to ‘fsetpos’ but the file position used
     for positioning is provided in a variable of type ‘fpos64_t’ to
     which POSITION points.

     If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32
     bits machine this function is available under the name ‘fsetpos’
     and so transparently replaces the old interface.


File: libc.info,  Node: Stream Buffering,  Next: Other Kinds of Streams,  Prev: Portable Positioning,  Up: I/O on Streams

12.20 Stream Buffering
======================

Characters that are written to a stream are normally accumulated and
transmitted asynchronously to the file in a block, instead of appearing
as soon as they are output by the application program.  Similarly,
streams often retrieve input from the host environment in blocks rather
than on a character-by-character basis.  This is called "buffering".

   If you are writing programs that do interactive input and output
using streams, you need to understand how buffering works when you
design the user interface to your program.  Otherwise, you might find
that output (such as progress or prompt messages) doesn’t appear when
you intended it to, or displays some other unexpected behavior.

   This section deals only with controlling when characters are
transmitted between the stream and the file or device, and _not_ with
how things like echoing, flow control, and the like are handled on
specific classes of devices.  For information on common control
operations on terminal devices, see *note Low-Level Terminal
Interface::.

   You can bypass the stream buffering facilities altogether by using
the low-level input and output functions that operate on file
descriptors instead.  *Note Low-Level I/O::.

* Menu:

* Buffering Concepts::          Terminology is defined here.
* Flushing Buffers::            How to ensure that output buffers are flushed.
* Controlling Buffering::       How to specify what kind of buffering to use.


File: libc.info,  Node: Buffering Concepts,  Next: Flushing Buffers,  Up: Stream Buffering

12.20.1 Buffering Concepts
--------------------------

There are three different kinds of buffering strategies:

   • Characters written to or read from an "unbuffered" stream are
     transmitted individually to or from the file as soon as possible.

   • Characters written to a "line buffered" stream are transmitted to
     the file in blocks when a newline character is encountered.

   • Characters written to or read from a "fully buffered" stream are
     transmitted to or from the file in blocks of arbitrary size.

   Newly opened streams are normally fully buffered, with one exception:
a stream connected to an interactive device such as a terminal is
initially line buffered.  *Note Controlling Buffering::, for information
on how to select a different kind of buffering.  Usually the automatic
selection gives you the most convenient kind of buffering for the file
or device you open.

   The use of line buffering for interactive devices implies that output
messages ending in a newline will appear immediately—which is usually
what you want.  Output that doesn’t end in a newline might or might not
show up immediately, so if you want them to appear immediately, you
should flush buffered output explicitly with ‘fflush’, as described in
*note Flushing Buffers::.


File: libc.info,  Node: Flushing Buffers,  Next: Controlling Buffering,  Prev: Buffering Concepts,  Up: Stream Buffering

12.20.2 Flushing Buffers
------------------------

"Flushing" output on a buffered stream means transmitting all
accumulated characters to the file.  There are many circumstances when
buffered output on a stream is flushed automatically:

   • When you try to do output and the output buffer is full.

   • When the stream is closed.  *Note Closing Streams::.

   • When the program terminates by calling ‘exit’.  *Note Normal
     Termination::.

   • When a newline is written, if the stream is line buffered.

   • Whenever an input operation on _any_ stream actually reads data
     from its file.

   If you want to flush the buffered output at another time, call
‘fflush’, which is declared in the header file ‘stdio.h’.

 -- Function: int fflush (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function causes any buffered output on STREAM to be delivered
     to the file.  If STREAM is a null pointer, then ‘fflush’ causes
     buffered output on _all_ open output streams to be flushed.

     This function returns ‘EOF’ if a write error occurs, or zero
     otherwise.

 -- Function: int fflush_unlocked (FILE *STREAM)

     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘fflush_unlocked’ function is equivalent to the ‘fflush’
     function except that it does not implicitly lock the stream.

   The ‘fflush’ function can be used to flush all streams currently
opened.  While this is useful in some situations it does often more than
necessary since it might be done in situations when terminal input is
required and the program wants to be sure that all output is visible on
the terminal.  But this means that only line buffered streams have to be
flushed.  Solaris introduced a function especially for this.  It was
always available in the GNU C Library in some form but never officially
exported.

 -- Function: void _flushlbf (void)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     The ‘_flushlbf’ function flushes all line buffered streams
     currently opened.

     This function is declared in the ‘stdio_ext.h’ header.

   *Compatibility Note:* Some brain-damaged operating systems have been
known to be so thoroughly fixated on line-oriented input and output that
flushing a line buffered stream causes a newline to be written!
Fortunately, this “feature” seems to be becoming less common.  You do
not need to worry about this with the GNU C Library.

   In some situations it might be useful to not flush the output pending
for a stream but instead simply forget it.  If transmission is costly
and the output is not needed anymore this is valid reasoning.  In this
situation a non-standard function introduced in Solaris and available in
the GNU C Library can be used.

 -- Function: void __fpurge (FILE *STREAM)

     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Unsafe
     corrupt | *Note POSIX Safety Concepts::.

     The ‘__fpurge’ function causes the buffer of the stream STREAM to
     be emptied.  If the stream is currently in read mode all input in
     the buffer is lost.  If the stream is in output mode the buffered
     output is not written to the device (or whatever other underlying
     storage) and the buffer is cleared.

     This function is declared in ‘stdio_ext.h’.


File: libc.info,  Node: Controlling Buffering,  Prev: Flushing Buffers,  Up: Stream Buffering

12.20.3 Controlling Which Kind of Buffering
-------------------------------------------

After opening a stream (but before any other operations have been
performed on it), you can explicitly specify what kind of buffering you
want it to have using the ‘setvbuf’ function.

   The facilities listed in this section are declared in the header file
‘stdio.h’.

 -- Function: int setvbuf (FILE *STREAM, char *BUF, int MODE, size_t
          SIZE)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function is used to specify that the stream STREAM should have
     the buffering mode MODE, which can be either ‘_IOFBF’ (for full
     buffering), ‘_IOLBF’ (for line buffering), or ‘_IONBF’ (for
     unbuffered input/output).

     If you specify a null pointer as the BUF argument, then ‘setvbuf’
     allocates a buffer itself using ‘malloc’.  This buffer will be
     freed when you close the stream.

     Otherwise, BUF should be a character array that can hold at least
     SIZE characters.  You should not free the space for this array as
     long as the stream remains open and this array remains its buffer.
     You should usually either allocate it statically, or ‘malloc’
     (*note Unconstrained Allocation::) the buffer.  Using an automatic
     array is not a good idea unless you close the file before exiting
     the block that declares the array.

     While the array remains a stream buffer, the stream I/O functions
     will use the buffer for their internal purposes.  You shouldn’t try
     to access the values in the array directly while the stream is
     using it for buffering.

     The ‘setvbuf’ function returns zero on success, or a nonzero value
     if the value of MODE is not valid or if the request could not be
     honored.

 -- Macro: int _IOFBF

     The value of this macro is an integer constant expression that can
     be used as the MODE argument to the ‘setvbuf’ function to specify
     that the stream should be fully buffered.

 -- Macro: int _IOLBF

     The value of this macro is an integer constant expression that can
     be used as the MODE argument to the ‘setvbuf’ function to specify
     that the stream should be line buffered.

 -- Macro: int _IONBF

     The value of this macro is an integer constant expression that can
     be used as the MODE argument to the ‘setvbuf’ function to specify
     that the stream should be unbuffered.

 -- Macro: int BUFSIZ

     The value of this macro is an integer constant expression that is
     good to use for the SIZE argument to ‘setvbuf’.  This value is
     guaranteed to be at least ‘256’.

     The value of ‘BUFSIZ’ is chosen on each system so as to make stream
     I/O efficient.  So it is a good idea to use ‘BUFSIZ’ as the size
     for the buffer when you call ‘setvbuf’.

     Actually, you can get an even better value to use for the buffer
     size by means of the ‘fstat’ system call: it is found in the
     ‘st_blksize’ field of the file attributes.  *Note Attribute
     Meanings::.

     Sometimes people also use ‘BUFSIZ’ as the allocation size of
     buffers used for related purposes, such as strings used to receive
     a line of input with ‘fgets’ (*note Character Input::).  There is
     no particular reason to use ‘BUFSIZ’ for this instead of any other
     integer, except that it might lead to doing I/O in chunks of an
     efficient size.

 -- Function: void setbuf (FILE *STREAM, char *BUF)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     If BUF is a null pointer, the effect of this function is equivalent
     to calling ‘setvbuf’ with a MODE argument of ‘_IONBF’.  Otherwise,
     it is equivalent to calling ‘setvbuf’ with BUF, and a MODE of
     ‘_IOFBF’ and a SIZE argument of ‘BUFSIZ’.

     The ‘setbuf’ function is provided for compatibility with old code;
     use ‘setvbuf’ in all new programs.

 -- Function: void setbuffer (FILE *STREAM, char *BUF, size_t SIZE)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     If BUF is a null pointer, this function makes STREAM unbuffered.
     Otherwise, it makes STREAM fully buffered using BUF as the buffer.
     The SIZE argument specifies the length of BUF.

     This function is provided for compatibility with old BSD code.  Use
     ‘setvbuf’ instead.

 -- Function: void setlinebuf (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Unsafe corrupt | AC-Unsafe lock corrupt
     | *Note POSIX Safety Concepts::.

     This function makes STREAM be line buffered, and allocates the
     buffer for you.

     This function is provided for compatibility with old BSD code.  Use
     ‘setvbuf’ instead.

   It is possible to query whether a given stream is line buffered or
not using a non-standard function introduced in Solaris and available in
the GNU C Library.

 -- Function: int __flbf (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘__flbf’ function will return a nonzero value in case the
     stream STREAM is line buffered.  Otherwise the return value is
     zero.

     This function is declared in the ‘stdio_ext.h’ header.

   Two more extensions allow to determine the size of the buffer and how
much of it is used.  These functions were also introduced in Solaris.

 -- Function: size_t __fbufsize (FILE *STREAM)

     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Safe |
     *Note POSIX Safety Concepts::.

     The ‘__fbufsize’ function return the size of the buffer in the
     stream STREAM.  This value can be used to optimize the use of the
     stream.

     This function is declared in the ‘stdio_ext.h’ header.

 -- Function: size_t __fpending (FILE *STREAM)

     Preliminary: | MT-Safe race:stream | AS-Unsafe corrupt | AC-Safe |
     *Note POSIX Safety Concepts::.

     The ‘__fpending’ function returns the number of bytes currently in
     the output buffer.  For wide-oriented streams the measuring unit is
     wide characters.  This function should not be used on buffers in
     read mode or opened read-only.

     This function is declared in the ‘stdio_ext.h’ header.


File: libc.info,  Node: Other Kinds of Streams,  Next: Formatted Messages,  Prev: Stream Buffering,  Up: I/O on Streams

12.21 Other Kinds of Streams
============================

The GNU C Library provides ways for you to define additional kinds of
streams that do not necessarily correspond to an open file.

   One such type of stream takes input from or writes output to a
string.  These kinds of streams are used internally to implement the
‘sprintf’ and ‘sscanf’ functions.  You can also create such a stream
explicitly, using the functions described in *note String Streams::.

   More generally, you can define streams that do input/output to
arbitrary objects using functions supplied by your program.  This
protocol is discussed in *note Custom Streams::.

   *Portability Note:* The facilities described in this section are
specific to GNU. Other systems or C implementations might or might not
provide equivalent functionality.

* Menu:

* String Streams::              Streams that get data from or put data in
				 a string or memory buffer.
* Custom Streams::              Defining your own streams with an arbitrary
				 input data source and/or output data sink.


File: libc.info,  Node: String Streams,  Next: Custom Streams,  Up: Other Kinds of Streams

12.21.1 String Streams
----------------------

The ‘fmemopen’ and ‘open_memstream’ functions allow you to do I/O to a
string or memory buffer.  These facilities are declared in ‘stdio.h’.

 -- Function: FILE * fmemopen (void *BUF, size_t SIZE, const char
          *OPENTYPE)

     Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe mem lock |
     *Note POSIX Safety Concepts::.

     This function opens a stream that allows the access specified by
     the OPENTYPE argument, that reads from or writes to the buffer
     specified by the argument BUF.  This array must be at least SIZE
     bytes long.

     If you specify a null pointer as the BUF argument, ‘fmemopen’
     dynamically allocates an array SIZE bytes long (as with ‘malloc’;
     *note Unconstrained Allocation::).  This is really only useful if
     you are going to write things to the buffer and then read them back
     in again, because you have no way of actually getting a pointer to
     the buffer (for this, try ‘open_memstream’, below).  The buffer is
     freed when the stream is closed.

     The argument OPENTYPE is the same as in ‘fopen’ (*note Opening
     Streams::).  If the OPENTYPE specifies append mode, then the
     initial file position is set to the first null character in the
     buffer.  Otherwise the initial file position is at the beginning of
     the buffer.

     When a stream open for writing is flushed or closed, a null
     character (zero byte) is written at the end of the buffer if it
     fits.  You should add an extra byte to the SIZE argument to account
     for this.  Attempts to write more than SIZE bytes to the buffer
     result in an error.

     For a stream open for reading, null characters (zero bytes) in the
     buffer do not count as “end of file”.  Read operations indicate end
     of file only when the file position advances past SIZE bytes.  So,
     if you want to read characters from a null-terminated string, you
     should supply the length of the string as the SIZE argument.

   Here is an example of using ‘fmemopen’ to create a stream for reading
from a string:


     #include <stdio.h>

     static char buffer[] = "foobar";

     int
     main (void)
     {
       int ch;
       FILE *stream;

       stream = fmemopen (buffer, strlen (buffer), "r");
       while ((ch = fgetc (stream)) != EOF)
         printf ("Got %c\n", ch);
       fclose (stream);

       return 0;
     }

   This program produces the following output:

     Got f
     Got o
     Got o
     Got b
     Got a
     Got r

 -- Function: FILE * open_memstream (char **PTR, size_t *SIZELOC)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note
     POSIX Safety Concepts::.

     This function opens a stream for writing to a buffer.  The buffer
     is allocated dynamically and grown as necessary, using ‘malloc’.
     After you’ve closed the stream, this buffer is your responsibility
     to clean up using ‘free’ or ‘realloc’.  *Note Unconstrained
     Allocation::.

     When the stream is closed with ‘fclose’ or flushed with ‘fflush’,
     the locations PTR and SIZELOC are updated to contain the pointer to
     the buffer and its size.  The values thus stored remain valid only
     as long as no further output on the stream takes place.  If you do
     more output, you must flush the stream again to store new values
     before you use them again.

     A null character is written at the end of the buffer.  This null
     character is _not_ included in the size value stored at SIZELOC.

     You can move the stream’s file position with ‘fseek’ or ‘fseeko’
     (*note File Positioning::).  Moving the file position past the end
     of the data already written fills the intervening space with
     zeroes.

   Here is an example of using ‘open_memstream’:


     #include <stdio.h>

     int
     main (void)
     {
       char *bp;
       size_t size;
       FILE *stream;

       stream = open_memstream (&bp, &size);
       fprintf (stream, "hello");
       fflush (stream);
       printf ("buf = `%s', size = %zu\n", bp, size);
       fprintf (stream, ", world");
       fclose (stream);
       printf ("buf = `%s', size = %zu\n", bp, size);

       return 0;
     }

   This program produces the following output:

     buf = `hello', size = 5
     buf = `hello, world', size = 12


File: libc.info,  Node: Custom Streams,  Prev: String Streams,  Up: Other Kinds of Streams

12.21.2 Programming Your Own Custom Streams
-------------------------------------------

This section describes how you can make a stream that gets input from an
arbitrary data source or writes output to an arbitrary data sink
programmed by you.  We call these "custom streams".  The functions and
types described here are all GNU extensions.

* Menu:

* Streams and Cookies::         The "cookie" records where to fetch or
				 store data that is read or written.
* Hook Functions::              How you should define the four "hook
				 functions" that a custom stream needs.


File: libc.info,  Node: Streams and Cookies,  Next: Hook Functions,  Up: Custom Streams

12.21.2.1 Custom Streams and Cookies
....................................

Inside every custom stream is a special object called the "cookie".
This is an object supplied by you which records where to fetch or store
the data read or written.  It is up to you to define a data type to use
for the cookie.  The stream functions in the library never refer
directly to its contents, and they don’t even know what the type is;
they record its address with type ‘void *’.

   To implement a custom stream, you must specify _how_ to fetch or
store the data in the specified place.  You do this by defining "hook
functions" to read, write, change “file position”, and close the stream.
All four of these functions will be passed the stream’s cookie so they
can tell where to fetch or store the data.  The library functions don’t
know what’s inside the cookie, but your functions will know.

   When you create a custom stream, you must specify the cookie pointer,
and also the four hook functions stored in a structure of type
‘cookie_io_functions_t’.

   These facilities are declared in ‘stdio.h’.

 -- Data Type: cookie_io_functions_t

     This is a structure type that holds the functions that define the
     communications protocol between the stream and its cookie.  It has
     the following members:

     ‘cookie_read_function_t *read’
          This is the function that reads data from the cookie.  If the
          value is a null pointer instead of a function, then read
          operations on this stream always return ‘EOF’.

     ‘cookie_write_function_t *write’
          This is the function that writes data to the cookie.  If the
          value is a null pointer instead of a function, then data
          written to the stream is discarded.

     ‘cookie_seek_function_t *seek’
          This is the function that performs the equivalent of file
          positioning on the cookie.  If the value is a null pointer
          instead of a function, calls to ‘fseek’ or ‘fseeko’ on this
          stream can only seek to locations within the buffer; any
          attempt to seek outside the buffer will return an ‘ESPIPE’
          error.

     ‘cookie_close_function_t *close’
          This function performs any appropriate cleanup on the cookie
          when closing the stream.  If the value is a null pointer
          instead of a function, nothing special is done to close the
          cookie when the stream is closed.

 -- Function: FILE * fopencookie (void *COOKIE, const char *OPENTYPE,
          cookie_io_functions_t IO-FUNCTIONS)

     Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe mem lock |
     *Note POSIX Safety Concepts::.

     This function actually creates the stream for communicating with
     the COOKIE using the functions in the IO-FUNCTIONS argument.  The
     OPENTYPE argument is interpreted as for ‘fopen’; see *note Opening
     Streams::.  (But note that the “truncate on open” option is
     ignored.)  The new stream is fully buffered.

     The ‘fopencookie’ function returns the newly created stream, or a
     null pointer in case of an error.


File: libc.info,  Node: Hook Functions,  Prev: Streams and Cookies,  Up: Custom Streams

12.21.2.2 Custom Stream Hook Functions
......................................

Here are more details on how you should define the four hook functions
that a custom stream needs.

   You should define the function to read data from the cookie as:

     ssize_t READER (void *COOKIE, char *BUFFER, size_t SIZE)

   This is very similar to the ‘read’ function; see *note I/O
Primitives::.  Your function should transfer up to SIZE bytes into the
BUFFER, and return the number of bytes read, or zero to indicate
end-of-file.  You can return a value of ‘-1’ to indicate an error.

   You should define the function to write data to the cookie as:

     ssize_t WRITER (void *COOKIE, const char *BUFFER, size_t SIZE)

   This is very similar to the ‘write’ function; see *note I/O
Primitives::.  Your function should transfer up to SIZE bytes from the
buffer, and return the number of bytes written.  You can return a value
of ‘0’ to indicate an error.  You must not return any negative value.

   You should define the function to perform seek operations on the
cookie as:

     int SEEKER (void *COOKIE, off64_t *POSITION, int WHENCE)

   For this function, the POSITION and WHENCE arguments are interpreted
as for ‘fgetpos’; see *note Portable Positioning::.

   After doing the seek operation, your function should store the
resulting file position relative to the beginning of the file in
POSITION.  Your function should return a value of ‘0’ on success and
‘-1’ to indicate an error.

   You should define the function to do cleanup operations on the cookie
appropriate for closing the stream as:

     int CLEANER (void *COOKIE)

   Your function should return ‘-1’ to indicate an error, and ‘0’
otherwise.

 -- Data Type: cookie_read_function_t

     This is the data type that the read function for a custom stream
     should have.  If you declare the function as shown above, this is
     the type it will have.

 -- Data Type: cookie_write_function_t

     The data type of the write function for a custom stream.

 -- Data Type: cookie_seek_function_t

     The data type of the seek function for a custom stream.

 -- Data Type: cookie_close_function_t

     The data type of the close function for a custom stream.


File: libc.info,  Node: Formatted Messages,  Prev: Other Kinds of Streams,  Up: I/O on Streams

12.22 Formatted Messages
========================

On systems which are based on System V messages of programs (especially
the system tools) are printed in a strict form using the ‘fmtmsg’
function.  The uniformity sometimes helps the user to interpret messages
and the strictness tests of the ‘fmtmsg’ function ensure that the
programmer follows some minimal requirements.

* Menu:

* Printing Formatted Messages::   The ‘fmtmsg’ function.
* Adding Severity Classes::       Add more severity classes.
* Example::                       How to use ‘fmtmsg’ and ‘addseverity’.


File: libc.info,  Node: Printing Formatted Messages,  Next: Adding Severity Classes,  Up: Formatted Messages

12.22.1 Printing Formatted Messages
-----------------------------------

Messages can be printed to standard error and/or to the console.  To
select the destination the programmer can use the following two values,
bitwise OR combined if wanted, for the CLASSIFICATION parameter of
‘fmtmsg’:

‘MM_PRINT’
     Display the message in standard error.
‘MM_CONSOLE’
     Display the message on the system console.

   The erroneous piece of the system can be signalled by exactly one of
the following values which also is bitwise ORed with the CLASSIFICATION
parameter to ‘fmtmsg’:

‘MM_HARD’
     The source of the condition is some hardware.
‘MM_SOFT’
     The source of the condition is some software.
‘MM_FIRM’
     The source of the condition is some firmware.

   A third component of the CLASSIFICATION parameter to ‘fmtmsg’ can
describe the part of the system which detects the problem.  This is done
by using exactly one of the following values:

‘MM_APPL’
     The erroneous condition is detected by the application.
‘MM_UTIL’
     The erroneous condition is detected by a utility.
‘MM_OPSYS’
     The erroneous condition is detected by the operating system.

   A last component of CLASSIFICATION can signal the results of this
message.  Exactly one of the following values can be used:

‘MM_RECOVER’
     It is a recoverable error.
‘MM_NRECOV’
     It is a non-recoverable error.

 -- Function: int fmtmsg (long int CLASSIFICATION, const char *LABEL,
          int SEVERITY, const char *TEXT, const char *ACTION, const char
          *TAG)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Safe | *Note POSIX
     Safety Concepts::.

     Display a message described by its parameters on the device(s)
     specified in the CLASSIFICATION parameter.  The LABEL parameter
     identifies the source of the message.  The string should consist of
     two colon separated parts where the first part has not more than 10
     and the second part not more than 14 characters.  The TEXT
     parameter describes the condition of the error, the ACTION
     parameter possible steps to recover from the error and the TAG
     parameter is a reference to the online documentation where more
     information can be found.  It should contain the LABEL value and a
     unique identification number.

     Each of the parameters can be a special value which means this
     value is to be omitted.  The symbolic names for these values are:

     ‘MM_NULLLBL’
          Ignore LABEL parameter.
     ‘MM_NULLSEV’
          Ignore SEVERITY parameter.
     ‘MM_NULLMC’
          Ignore CLASSIFICATION parameter.  This implies that nothing is
          actually printed.
     ‘MM_NULLTXT’
          Ignore TEXT parameter.
     ‘MM_NULLACT’
          Ignore ACTION parameter.
     ‘MM_NULLTAG’
          Ignore TAG parameter.

     There is another way certain fields can be omitted from the output
     to standard error.  This is described below in the description of
     environment variables influencing the behavior.

     The SEVERITY parameter can have one of the values in the following
     table:

     ‘MM_NOSEV’
          Nothing is printed, this value is the same as ‘MM_NULLSEV’.
     ‘MM_HALT’
          This value is printed as ‘HALT’.
     ‘MM_ERROR’
          This value is printed as ‘ERROR’.
     ‘MM_WARNING’
          This value is printed as ‘WARNING’.
     ‘MM_INFO’
          This value is printed as ‘INFO’.

     The numeric value of these five macros are between ‘0’ and ‘4’.
     Using the environment variable ‘SEV_LEVEL’ or using the
     ‘addseverity’ function one can add more severity levels with their
     corresponding string to print.  This is described below (*note
     Adding Severity Classes::).

     If no parameter is ignored the output looks like this:

          LABEL: SEVERITY-STRING: TEXT
          TO FIX: ACTION TAG

     The colons, new line characters and the ‘TO FIX’ string are
     inserted if necessary, i.e., if the corresponding parameter is not
     ignored.

     This function is specified in the X/Open Portability Guide.  It is
     also available on all systems derived from System V.

     The function returns the value ‘MM_OK’ if no error occurred.  If
     only the printing to standard error failed, it returns ‘MM_NOMSG’.
     If printing to the console fails, it returns ‘MM_NOCON’.  If
     nothing is printed ‘MM_NOTOK’ is returned.  Among situations where
     all outputs fail this last value is also returned if a parameter
     value is incorrect.

   There are two environment variables which influence the behavior of
‘fmtmsg’.  The first is ‘MSGVERB’.  It is used to control the output
actually happening on standard error (_not_ the console output).  Each
of the five fields can explicitly be enabled.  To do this the user has
to put the ‘MSGVERB’ variable with a format like the following in the
environment before calling the ‘fmtmsg’ function the first time:

     MSGVERB=KEYWORD[:KEYWORD[:…]]

   Valid KEYWORDs are ‘label’, ‘severity’, ‘text’, ‘action’, and ‘tag’.
If the environment variable is not given or is the empty string, a not
supported keyword is given or the value is somehow else invalid, no part
of the message is masked out.

   The second environment variable which influences the behavior of
‘fmtmsg’ is ‘SEV_LEVEL’.  This variable and the change in the behavior
of ‘fmtmsg’ is not specified in the X/Open Portability Guide.  It is
available in System V systems, though.  It can be used to introduce new
severity levels.  By default, only the five severity levels described
above are available.  Any other numeric value would make ‘fmtmsg’ print
nothing.

   If the user puts ‘SEV_LEVEL’ with a format like

     SEV_LEVEL=[DESCRIPTION[:DESCRIPTION[:…]]]

in the environment of the process before the first call to ‘fmtmsg’,
where DESCRIPTION has a value of the form

     SEVERITY-KEYWORD,LEVEL,PRINTSTRING

   The SEVERITY-KEYWORD part is not used by ‘fmtmsg’ but it has to be
present.  The LEVEL part is a string representation of a number.  The
numeric value must be a number greater than 4.  This value must be used
in the SEVERITY parameter of ‘fmtmsg’ to select this class.  It is not
possible to overwrite any of the predefined classes.  The PRINTSTRING is
the string printed when a message of this class is processed by ‘fmtmsg’
(see above, ‘fmtsmg’ does not print the numeric value but instead the
string representation).


File: libc.info,  Node: Adding Severity Classes,  Next: Example,  Prev: Printing Formatted Messages,  Up: Formatted Messages

12.22.2 Adding Severity Classes
-------------------------------

There is another possibility to introduce severity classes besides using
the environment variable ‘SEV_LEVEL’.  This simplifies the task of
introducing new classes in a running program.  One could use the
‘setenv’ or ‘putenv’ function to set the environment variable, but this
is toilsome.

 -- Function: int addseverity (int SEVERITY, const char *STRING)
     Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe lock mem |
     *Note POSIX Safety Concepts::.

     This function allows the introduction of new severity classes which
     can be addressed by the SEVERITY parameter of the ‘fmtmsg’
     function.  The SEVERITY parameter of ‘addseverity’ must match the
     value for the parameter with the same name of ‘fmtmsg’, and STRING
     is the string printed in the actual messages instead of the numeric
     value.

     If STRING is ‘NULL’ the severity class with the numeric value
     according to SEVERITY is removed.

     It is not possible to overwrite or remove one of the default
     severity classes.  All calls to ‘addseverity’ with SEVERITY set to
     one of the values for the default classes will fail.

     The return value is ‘MM_OK’ if the task was successfully performed.
     If the return value is ‘MM_NOTOK’ something went wrong.  This could
     mean that no more memory is available or a class is not available
     when it has to be removed.

     This function is not specified in the X/Open Portability Guide
     although the ‘fmtsmg’ function is.  It is available on System V
     systems.


File: libc.info,  Node: Example,  Prev: Adding Severity Classes,  Up: Formatted Messages

12.22.3 How to use ‘fmtmsg’ and ‘addseverity’
---------------------------------------------

Here is a simple example program to illustrate the use of both functions
described in this section.


     #include <fmtmsg.h>

     int
     main (void)
     {
       addseverity (5, "NOTE2");
       fmtmsg (MM_PRINT, "only1field", MM_INFO, "text2", "action2", "tag2");
       fmtmsg (MM_PRINT, "UX:cat", 5, "invalid syntax", "refer to manual",
               "UX:cat:001");
       fmtmsg (MM_PRINT, "label:foo", 6, "text", "action", "tag");
       return 0;
     }

   The second call to ‘fmtmsg’ illustrates a use of this function as it
usually occurs on System V systems, which heavily use this function.  It
seems worthwhile to give a short explanation here of how this system
works on System V. The value of the LABEL field (‘UX:cat’) says that the
error occurred in the Unix program ‘cat’.  The explanation of the error
follows and the value for the ACTION parameter is ‘"refer to manual"’.
One could be more specific here, if necessary.  The TAG field contains,
as proposed above, the value of the string given for the LABEL
parameter, and additionally a unique ID (‘001’ in this case).  For a GNU
environment this string could contain a reference to the corresponding
node in the Info page for the program.

Running this program without specifying the ‘MSGVERB’ and ‘SEV_LEVEL’
function produces the following output:

     UX:cat: NOTE2: invalid syntax
     TO FIX: refer to manual UX:cat:001

   We see the different fields of the message and how the extra glue
(the colons and the ‘TO FIX’ string) is printed.  But only one of the
three calls to ‘fmtmsg’ produced output.  The first call does not print
anything because the LABEL parameter is not in the correct form.  The
string must contain two fields, separated by a colon (*note Printing
Formatted Messages::).  The third ‘fmtmsg’ call produced no output since
the class with the numeric value ‘6’ is not defined.  Although a class
with numeric value ‘5’ is also not defined by default, the call to
‘addseverity’ introduces it and the second call to ‘fmtmsg’ produces the
above output.

   When we change the environment of the program to contain
‘SEV_LEVEL=XXX,6,NOTE’ when running it we get a different result:

     UX:cat: NOTE2: invalid syntax
     TO FIX: refer to manual UX:cat:001
     label:foo: NOTE: text
     TO FIX: action tag

   Now the third call to ‘fmtmsg’ produced some output and we see how
the string ‘NOTE’ from the environment variable appears in the message.

   Now we can reduce the output by specifying which fields we are
interested in.  If we additionally set the environment variable
‘MSGVERB’ to the value ‘severity:label:action’ we get the following
output:

     UX:cat: NOTE2
     TO FIX: refer to manual
     label:foo: NOTE
     TO FIX: action

I.e., the output produced by the TEXT and the TAG parameters to ‘fmtmsg’
vanished.  Please also note that now there is no colon after the ‘NOTE’
and ‘NOTE2’ strings in the output.  This is not necessary since there is
no more output on this line because the text is missing.


File: libc.info,  Node: Low-Level I/O,  Next: File System Interface,  Prev: I/O on Streams,  Up: Top

13 Low-Level Input/Output
*************************

This chapter describes functions for performing low-level input/output
operations on file descriptors.  These functions include the primitives
for the higher-level I/O functions described in *note I/O on Streams::,
as well as functions for performing low-level control operations for
which there are no equivalents on streams.

   Stream-level I/O is more flexible and usually more convenient;
therefore, programmers generally use the descriptor-level functions only
when necessary.  These are some of the usual reasons:

   • For reading binary files in large chunks.

   • For reading an entire file into core before parsing it.

   • To perform operations other than data transfer, which can only be
     done with a descriptor.  (You can use ‘fileno’ to get the
     descriptor corresponding to a stream.)

   • To pass descriptors to a child process.  (The child can create its
     own stream to use a descriptor that it inherits, but cannot inherit
     a stream directly.)

* Menu:

* Opening and Closing Files::           How to open and close file
                                         descriptors.
* I/O Primitives::                      Reading and writing data.
* File Position Primitive::             Setting a descriptor’s file
                                         position.
* Descriptors and Streams::             Converting descriptor to stream
                                         or vice-versa.
* Stream/Descriptor Precautions::       Precautions needed if you use both
                                         descriptors and streams.
* Scatter-Gather::                      Fast I/O to discontinuous buffers.
* Copying File Data::                   Copying data between files.
* Memory-mapped I/O::                   Using files like memory.
* Waiting for I/O::                     How to check for input or output
					 on multiple file descriptors.
* Synchronizing I/O::                   Making sure all I/O actions completed.
* Asynchronous I/O::                    Perform I/O in parallel.
* Control Operations::                  Various other operations on file
					 descriptors.
* Duplicating Descriptors::             Fcntl commands for duplicating
                                         file descriptors.
* Descriptor Flags::                    Fcntl commands for manipulating
                                         flags associated with file
                                         descriptors.
* File Status Flags::                   Fcntl commands for manipulating
                                         flags associated with open files.
* File Locks::                          Fcntl commands for implementing
                                         file locking.
* Open File Description Locks::         Fcntl commands for implementing
                                         open file description locking.
* Open File Description Locks Example:: An example of open file description lock
                                         usage
* Interrupt Input::                     Getting an asynchronous signal when
                                         input arrives.
* IOCTLs::                              Generic I/O Control operations.


File: libc.info,  Node: Opening and Closing Files,  Next: I/O Primitives,  Up: Low-Level I/O

13.1 Opening and Closing Files
==============================

This section describes the primitives for opening and closing files
using file descriptors.  The ‘open’ and ‘creat’ functions are declared
in the header file ‘fcntl.h’, while ‘close’ is declared in ‘unistd.h’.

 -- Function: int open (const char *FILENAME, int FLAGS[, mode_t MODE])

     Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety
     Concepts::.

     The ‘open’ function creates and returns a new file descriptor for
     the file named by FILENAME.  Initially, the file position indicator
     for the file is at the beginning of the file.  The argument MODE
     (*note Permission Bits::) is used only when a file is created, but
     it doesn’t hurt to supply the argument in any case.

     The FLAGS argument controls how the file is to be opened.  This is
     a bit mask; you create the value by the bitwise OR of the
     appropriate parameters (using the ‘|’ operator in C). *Note File
     Status Flags::, for the parameters available.

     The normal return value from ‘open’ is a non-negative integer file
     descriptor.  In the case of an error, a value of -1 is returned
     instead.  In addition to the usual file name errors (*note File
     Name Errors::), the following ‘errno’ error conditions are defined
     for this function:

     ‘EACCES’
          The file exists but is not readable/writable as requested by
          the FLAGS argument, or the file does not exist and the
          directory is unwritable so it cannot be created.

     ‘EEXIST’
          Both ‘O_CREAT’ and ‘O_EXCL’ are set, and the named file
          already exists.

     ‘EINTR’
          The ‘open’ operation was interrupted by a signal.  *Note
          Interrupted Primitives::.

     ‘EISDIR’
          The FLAGS argument specified write access, and the file is a
          directory.

     ‘EMFILE’
          The process has too many files open.  The maximum number of
          file descriptors is controlled by the ‘RLIMIT_NOFILE’ resource
          limit; *note Limits on Resources::.

     ‘ENFILE’
          The entire system, or perhaps the file system which contains
          the directory, cannot support any additional open files at the
          moment.  (This problem cannot happen on GNU/Hurd systems.)

     ‘ENOENT’
          The named file does not exist, and ‘O_CREAT’ is not specified.

     ‘ENOSPC’
          The directory or file system that would contain the new file
          cannot be extended, because there is no disk space left.

     ‘ENXIO’
          ‘O_NONBLOCK’ and ‘O_WRONLY’ are both set in the FLAGS
          argument, the file named by FILENAME is a FIFO (*note Pipes
          and FIFOs::), and no process has the file open for reading.

     ‘EROFS’
          The file resides on a read-only file system and any of
          ‘O_WRONLY’, ‘O_RDWR’, and ‘O_TRUNC’ are set in the FLAGS
          argument, or ‘O_CREAT’ is set and the file does not already
          exist.

     If on a 32 bit machine the sources are translated with
     ‘_FILE_OFFSET_BITS == 64’ the function ‘open’ returns a file
     descriptor opened in the large file mode which enables the file
     handling functions to use files up to 2^63 bytes in size and offset
     from −2^63 to 2^63.  This happens transparently for the user since
     all of the low-level file handling functions are equally replaced.

     This function is a cancellation point in multi-threaded programs.
     This is a problem if the thread allocates some resources (like
     memory, file descriptors, semaphores or whatever) at the time
     ‘open’ is called.  If the thread gets canceled these resources stay
     allocated until the program ends.  To avoid this calls to ‘open’
     should be protected using cancellation handlers.

     The ‘open’ function is the underlying primitive for the ‘fopen’ and
     ‘freopen’ functions, that create streams.

 -- Function: int open64 (const char *FILENAME, int FLAGS[, mode_t
          MODE])

     Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety
     Concepts::.

     This function is similar to ‘open’.  It returns a file descriptor
     which can be used to access the file named by FILENAME.  The only
     difference is that on 32 bit systems the file is opened in the
     large file mode.  I.e., file length and file offsets can exceed 31
     bits.

     When the sources are translated with ‘_FILE_OFFSET_BITS == 64’ this
     function is actually available under the name ‘open’.  I.e., the
     new, extended API using 64 bit file sizes and offsets transparently
     replaces the old API.

 -- Obsolete function: int creat (const char *FILENAME, mode_t MODE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety
     Concepts::.

     This function is obsolete.  The call:

          creat (FILENAME, MODE)

     is equivalent to:

          open (FILENAME, O_WRONLY | O_CREAT | O_TRUNC, MODE)

     If on a 32 bit machine the sources are translated with
     ‘_FILE_OFFSET_BITS == 64’ the function ‘creat’ returns a file
     descriptor opened in the large file mode which enables the file
     handling functions to use files up to 2^63 in size and offset from
     −2^63 to 2^63.  This happens transparently for the user since all
     of the low-level file handling functions are equally replaced.

 -- Obsolete function: int creat64 (const char *FILENAME, mode_t MODE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety
     Concepts::.

     This function is similar to ‘creat’.  It returns a file descriptor
     which can be used to access the file named by FILENAME.  The only
     difference is that on 32 bit systems the file is opened in the
     large file mode.  I.e., file length and file offsets can exceed 31
     bits.

     To use this file descriptor one must not use the normal operations
     but instead the counterparts named ‘*64’, e.g., ‘read64’.

     When the sources are translated with ‘_FILE_OFFSET_BITS == 64’ this
     function is actually available under the name ‘open’.  I.e., the
     new, extended API using 64 bit file sizes and offsets transparently
     replaces the old API.

 -- Function: int close (int FILEDES)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety
     Concepts::.

     The function ‘close’ closes the file descriptor FILEDES.  Closing a
     file has the following consequences:

        • The file descriptor is deallocated.

        • Any record locks owned by the process on the file are
          unlocked.

        • When all file descriptors associated with a pipe or FIFO have
          been closed, any unread data is discarded.

     This function is a cancellation point in multi-threaded programs.
     This is a problem if the thread allocates some resources (like
     memory, file descriptors, semaphores or whatever) at the time
     ‘close’ is called.  If the thread gets canceled these resources
     stay allocated until the program ends.  To avoid this, calls to
     ‘close’ should be protected using cancellation handlers.

     The normal return value from ‘close’ is 0; a value of -1 is
     returned in case of failure.  The following ‘errno’ error
     conditions are defined for this function:

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor.

     ‘EINTR’
          The ‘close’ call was interrupted by a signal.  *Note
          Interrupted Primitives::.  Here is an example of how to handle
          ‘EINTR’ properly:

               TEMP_FAILURE_RETRY (close (desc));

     ‘ENOSPC’
     ‘EIO’
     ‘EDQUOT’
          When the file is accessed by NFS, these errors from ‘write’
          can sometimes not be detected until ‘close’.  *Note I/O
          Primitives::, for details on their meaning.

     Please note that there is _no_ separate ‘close64’ function.  This
     is not necessary since this function does not determine nor depend
     on the mode of the file.  The kernel which performs the ‘close’
     operation knows which mode the descriptor is used for and can
     handle this situation.

   To close a stream, call ‘fclose’ (*note Closing Streams::) instead of
trying to close its underlying file descriptor with ‘close’.  This
flushes any buffered output and updates the stream object to indicate
that it is closed.


File: libc.info,  Node: I/O Primitives,  Next: File Position Primitive,  Prev: Opening and Closing Files,  Up: Low-Level I/O

13.2 Input and Output Primitives
================================

This section describes the functions for performing primitive input and
output operations on file descriptors: ‘read’, ‘write’, and ‘lseek’.
These functions are declared in the header file ‘unistd.h’.

 -- Data Type: ssize_t

     This data type is used to represent the sizes of blocks that can be
     read or written in a single operation.  It is similar to ‘size_t’,
     but must be a signed type.

 -- Function: ssize_t read (int FILEDES, void *BUFFER, size_t SIZE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘read’ function reads up to SIZE bytes from the file with
     descriptor FILEDES, storing the results in the BUFFER.  (This is
     not necessarily a character string, and no terminating null
     character is added.)

     The return value is the number of bytes actually read.  This might
     be less than SIZE; for example, if there aren’t that many bytes
     left in the file or if there aren’t that many bytes immediately
     available.  The exact behavior depends on what kind of file it is.
     Note that reading less than SIZE bytes is not an error.

     A value of zero indicates end-of-file (except if the value of the
     SIZE argument is also zero).  This is not considered an error.  If
     you keep calling ‘read’ while at end-of-file, it will keep
     returning zero and doing nothing else.

     If ‘read’ returns at least one character, there is no way you can
     tell whether end-of-file was reached.  But if you did reach the
     end, the next read will return zero.

     In case of an error, ‘read’ returns -1.  The following ‘errno’
     error conditions are defined for this function:

     ‘EAGAIN’
          Normally, when no input is immediately available, ‘read’ waits
          for some input.  But if the ‘O_NONBLOCK’ flag is set for the
          file (*note File Status Flags::), ‘read’ returns immediately
          without reading any data, and reports this error.

          *Compatibility Note:* Most versions of BSD Unix use a
          different error code for this: ‘EWOULDBLOCK’.  In the GNU C
          Library, ‘EWOULDBLOCK’ is an alias for ‘EAGAIN’, so it doesn’t
          matter which name you use.

          On some systems, reading a large amount of data from a
          character special file can also fail with ‘EAGAIN’ if the
          kernel cannot find enough physical memory to lock down the
          user’s pages.  This is limited to devices that transfer with
          direct memory access into the user’s memory, which means it
          does not include terminals, since they always use separate
          buffers inside the kernel.  This problem never happens on
          GNU/Hurd systems.

          Any condition that could result in ‘EAGAIN’ can instead result
          in a successful ‘read’ which returns fewer bytes than
          requested.  Calling ‘read’ again immediately would result in
          ‘EAGAIN’.

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor, or is not
          open for reading.

     ‘EINTR’
          ‘read’ was interrupted by a signal while it was waiting for
          input.  *Note Interrupted Primitives::.  A signal will not
          necessarily cause ‘read’ to return ‘EINTR’; it may instead
          result in a successful ‘read’ which returns fewer bytes than
          requested.

     ‘EIO’
          For many devices, and for disk files, this error code
          indicates a hardware error.

          ‘EIO’ also occurs when a background process tries to read from
          the controlling terminal, and the normal action of stopping
          the process by sending it a ‘SIGTTIN’ signal isn’t working.
          This might happen if the signal is being blocked or ignored,
          or because the process group is orphaned.  *Note Job
          Control::, for more information about job control, and *note
          Signal Handling::, for information about signals.

     ‘EINVAL’
          In some systems, when reading from a character or block
          device, position and size offsets must be aligned to a
          particular block size.  This error indicates that the offsets
          were not properly aligned.

     Please note that there is no function named ‘read64’.  This is not
     necessary since this function does not directly modify or handle
     the possibly wide file offset.  Since the kernel handles this state
     internally, the ‘read’ function can be used for all cases.

     This function is a cancellation point in multi-threaded programs.
     This is a problem if the thread allocates some resources (like
     memory, file descriptors, semaphores or whatever) at the time
     ‘read’ is called.  If the thread gets canceled these resources stay
     allocated until the program ends.  To avoid this, calls to ‘read’
     should be protected using cancellation handlers.

     The ‘read’ function is the underlying primitive for all of the
     functions that read from streams, such as ‘fgetc’.

 -- Function: ssize_t pread (int FILEDES, void *BUFFER, size_t SIZE,
          off_t OFFSET)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘pread’ function is similar to the ‘read’ function.  The first
     three arguments are identical, and the return values and error
     codes also correspond.

     The difference is the fourth argument and its handling.  The data
     block is not read from the current position of the file descriptor
     ‘filedes’.  Instead the data is read from the file starting at
     position OFFSET.  The position of the file descriptor itself is not
     affected by the operation.  The value is the same as before the
     call.

     When the source file is compiled with ‘_FILE_OFFSET_BITS == 64’ the
     ‘pread’ function is in fact ‘pread64’ and the type ‘off_t’ has 64
     bits, which makes it possible to handle files up to 2^63 bytes in
     length.

     The return value of ‘pread’ describes the number of bytes read.  In
     the error case it returns -1 like ‘read’ does and the error codes
     are also the same, with these additions:

     ‘EINVAL’
          The value given for OFFSET is negative and therefore illegal.

     ‘ESPIPE’
          The file descriptor FILEDES is associated with a pipe or a
          FIFO and this device does not allow positioning of the file
          pointer.

     The function is an extension defined in the Unix Single
     Specification version 2.

 -- Function: ssize_t pread64 (int FILEDES, void *BUFFER, size_t SIZE,
          off64_t OFFSET)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is similar to the ‘pread’ function.  The difference
     is that the OFFSET parameter is of type ‘off64_t’ instead of
     ‘off_t’ which makes it possible on 32 bit machines to address files
     larger than 2^31 bytes and up to 2^63 bytes.  The file descriptor
     ‘filedes’ must be opened using ‘open64’ since otherwise the large
     offsets possible with ‘off64_t’ will lead to errors with a
     descriptor in small file mode.

     When the source file is compiled with ‘_FILE_OFFSET_BITS == 64’ on
     a 32 bit machine this function is actually available under the name
     ‘pread’ and so transparently replaces the 32 bit interface.

 -- Function: ssize_t write (int FILEDES, const void *BUFFER, size_t
          SIZE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘write’ function writes up to SIZE bytes from BUFFER to the
     file with descriptor FILEDES.  The data in BUFFER is not
     necessarily a character string and a null character is output like
     any other character.

     The return value is the number of bytes actually written.  This may
     be SIZE, but can always be smaller.  Your program should always
     call ‘write’ in a loop, iterating until all the data is written.

     Once ‘write’ returns, the data is enqueued to be written and can be
     read back right away, but it is not necessarily written out to
     permanent storage immediately.  You can use ‘fsync’ when you need
     to be sure your data has been permanently stored before continuing.
     (It is more efficient for the system to batch up consecutive writes
     and do them all at once when convenient.  Normally they will always
     be written to disk within a minute or less.)  Modern systems
     provide another function ‘fdatasync’ which guarantees integrity
     only for the file data and is therefore faster.  You can use the
     ‘O_FSYNC’ open mode to make ‘write’ always store the data to disk
     before returning; *note Operating Modes::.

     In the case of an error, ‘write’ returns -1.  The following ‘errno’
     error conditions are defined for this function:

     ‘EAGAIN’
          Normally, ‘write’ blocks until the write operation is
          complete.  But if the ‘O_NONBLOCK’ flag is set for the file
          (*note Control Operations::), it returns immediately without
          writing any data and reports this error.  An example of a
          situation that might cause the process to block on output is
          writing to a terminal device that supports flow control, where
          output has been suspended by receipt of a STOP character.

          *Compatibility Note:* Most versions of BSD Unix use a
          different error code for this: ‘EWOULDBLOCK’.  In the GNU C
          Library, ‘EWOULDBLOCK’ is an alias for ‘EAGAIN’, so it doesn’t
          matter which name you use.

          On some systems, writing a large amount of data from a
          character special file can also fail with ‘EAGAIN’ if the
          kernel cannot find enough physical memory to lock down the
          user’s pages.  This is limited to devices that transfer with
          direct memory access into the user’s memory, which means it
          does not include terminals, since they always use separate
          buffers inside the kernel.  This problem does not arise on
          GNU/Hurd systems.

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor, or is not
          open for writing.

     ‘EFBIG’
          The size of the file would become larger than the
          implementation can support.

     ‘EINTR’
          The ‘write’ operation was interrupted by a signal while it was
          blocked waiting for completion.  A signal will not necessarily
          cause ‘write’ to return ‘EINTR’; it may instead result in a
          successful ‘write’ which writes fewer bytes than requested.
          *Note Interrupted Primitives::.

     ‘EIO’
          For many devices, and for disk files, this error code
          indicates a hardware error.

     ‘ENOSPC’
          The device containing the file is full.

     ‘EPIPE’
          This error is returned when you try to write to a pipe or FIFO
          that isn’t open for reading by any process.  When this
          happens, a ‘SIGPIPE’ signal is also sent to the process; see
          *note Signal Handling::.

     ‘EINVAL’
          In some systems, when writing to a character or block device,
          position and size offsets must be aligned to a particular
          block size.  This error indicates that the offsets were not
          properly aligned.

     Unless you have arranged to prevent ‘EINTR’ failures, you should
     check ‘errno’ after each failing call to ‘write’, and if the error
     was ‘EINTR’, you should simply repeat the call.  *Note Interrupted
     Primitives::.  The easy way to do this is with the macro
     ‘TEMP_FAILURE_RETRY’, as follows:

          nbytes = TEMP_FAILURE_RETRY (write (desc, buffer, count));

     Please note that there is no function named ‘write64’.  This is not
     necessary since this function does not directly modify or handle
     the possibly wide file offset.  Since the kernel handles this state
     internally the ‘write’ function can be used for all cases.

     This function is a cancellation point in multi-threaded programs.
     This is a problem if the thread allocates some resources (like
     memory, file descriptors, semaphores or whatever) at the time
     ‘write’ is called.  If the thread gets canceled these resources
     stay allocated until the program ends.  To avoid this, calls to
     ‘write’ should be protected using cancellation handlers.

     The ‘write’ function is the underlying primitive for all of the
     functions that write to streams, such as ‘fputc’.

 -- Function: ssize_t pwrite (int FILEDES, const void *BUFFER, size_t
          SIZE, off_t OFFSET)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘pwrite’ function is similar to the ‘write’ function.  The
     first three arguments are identical, and the return values and
     error codes also correspond.

     The difference is the fourth argument and its handling.  The data
     block is not written to the current position of the file descriptor
     ‘filedes’.  Instead the data is written to the file starting at
     position OFFSET.  The position of the file descriptor itself is not
     affected by the operation.  The value is the same as before the
     call.

     However, on Linux, if a file is opened with ‘O_APPEND’, ‘pwrite’
     appends data to the end of the file, regardless of the value of
     ‘offset’.

     When the source file is compiled with ‘_FILE_OFFSET_BITS == 64’ the
     ‘pwrite’ function is in fact ‘pwrite64’ and the type ‘off_t’ has 64
     bits, which makes it possible to handle files up to 2^63 bytes in
     length.

     The return value of ‘pwrite’ describes the number of written bytes.
     In the error case it returns -1 like ‘write’ does and the error
     codes are also the same, with these additions:

     ‘EINVAL’
          The value given for OFFSET is negative and therefore illegal.

     ‘ESPIPE’
          The file descriptor FILEDES is associated with a pipe or a
          FIFO and this device does not allow positioning of the file
          pointer.

     The function is an extension defined in the Unix Single
     Specification version 2.

 -- Function: ssize_t pwrite64 (int FILEDES, const void *BUFFER, size_t
          SIZE, off64_t OFFSET)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is similar to the ‘pwrite’ function.  The difference
     is that the OFFSET parameter is of type ‘off64_t’ instead of
     ‘off_t’ which makes it possible on 32 bit machines to address files
     larger than 2^31 bytes and up to 2^63 bytes.  The file descriptor
     ‘filedes’ must be opened using ‘open64’ since otherwise the large
     offsets possible with ‘off64_t’ will lead to errors with a
     descriptor in small file mode.

     When the source file is compiled using ‘_FILE_OFFSET_BITS == 64’ on
     a 32 bit machine this function is actually available under the name
     ‘pwrite’ and so transparently replaces the 32 bit interface.


File: libc.info,  Node: File Position Primitive,  Next: Descriptors and Streams,  Prev: I/O Primitives,  Up: Low-Level I/O

13.3 Setting the File Position of a Descriptor
==============================================

Just as you can set the file position of a stream with ‘fseek’, you can
set the file position of a descriptor with ‘lseek’.  This specifies the
position in the file for the next ‘read’ or ‘write’ operation.  *Note
File Positioning::, for more information on the file position and what
it means.

   To read the current file position value from a descriptor, use ‘lseek
(DESC, 0, SEEK_CUR)’.

 -- Function: off_t lseek (int FILEDES, off_t OFFSET, int WHENCE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘lseek’ function is used to change the file position of the
     file with descriptor FILEDES.

     The WHENCE argument specifies how the OFFSET should be interpreted,
     in the same way as for the ‘fseek’ function, and it must be one of
     the symbolic constants ‘SEEK_SET’, ‘SEEK_CUR’, or ‘SEEK_END’.

     ‘SEEK_SET’
          Specifies that OFFSET is a count of characters from the
          beginning of the file.

     ‘SEEK_CUR’
          Specifies that OFFSET is a count of characters from the
          current file position.  This count may be positive or
          negative.

     ‘SEEK_END’
          Specifies that OFFSET is a count of characters from the end of
          the file.  A negative count specifies a position within the
          current extent of the file; a positive count specifies a
          position past the current end.  If you set the position past
          the current end, and actually write data, you will extend the
          file with zeros up to that position.

     The return value from ‘lseek’ is normally the resulting file
     position, measured in bytes from the beginning of the file.  You
     can use this feature together with ‘SEEK_CUR’ to read the current
     file position.

     If you want to append to the file, setting the file position to the
     current end of file with ‘SEEK_END’ is not sufficient.  Another
     process may write more data after you seek but before you write,
     extending the file so the position you write onto clobbers their
     data.  Instead, use the ‘O_APPEND’ operating mode; *note Operating
     Modes::.

     You can set the file position past the current end of the file.
     This does not by itself make the file longer; ‘lseek’ never changes
     the file.  But subsequent output at that position will extend the
     file.  Characters between the previous end of file and the new
     position are filled with zeros.  Extending the file in this way can
     create a “hole”: the blocks of zeros are not actually allocated on
     disk, so the file takes up less space than it appears to; it is
     then called a “sparse file”.

     If the file position cannot be changed, or the operation is in some
     way invalid, ‘lseek’ returns a value of -1.  The following ‘errno’
     error conditions are defined for this function:

     ‘EBADF’
          The FILEDES is not a valid file descriptor.

     ‘EINVAL’
          The WHENCE argument value is not valid, or the resulting file
          offset is not valid.  A file offset is invalid.

     ‘ESPIPE’
          The FILEDES corresponds to an object that cannot be
          positioned, such as a pipe, FIFO or terminal device.  (POSIX.1
          specifies this error only for pipes and FIFOs, but on GNU
          systems, you always get ‘ESPIPE’ if the object is not
          seekable.)

     When the source file is compiled with ‘_FILE_OFFSET_BITS == 64’ the
     ‘lseek’ function is in fact ‘lseek64’ and the type ‘off_t’ has 64
     bits which makes it possible to handle files up to 2^63 bytes in
     length.

     This function is a cancellation point in multi-threaded programs.
     This is a problem if the thread allocates some resources (like
     memory, file descriptors, semaphores or whatever) at the time
     ‘lseek’ is called.  If the thread gets canceled these resources
     stay allocated until the program ends.  To avoid this calls to
     ‘lseek’ should be protected using cancellation handlers.

     The ‘lseek’ function is the underlying primitive for the ‘fseek’,
     ‘fseeko’, ‘ftell’, ‘ftello’ and ‘rewind’ functions, which operate
     on streams instead of file descriptors.

 -- Function: off64_t lseek64 (int FILEDES, off64_t OFFSET, int WHENCE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is similar to the ‘lseek’ function.  The difference
     is that the OFFSET parameter is of type ‘off64_t’ instead of
     ‘off_t’ which makes it possible on 32 bit machines to address files
     larger than 2^31 bytes and up to 2^63 bytes.  The file descriptor
     ‘filedes’ must be opened using ‘open64’ since otherwise the large
     offsets possible with ‘off64_t’ will lead to errors with a
     descriptor in small file mode.

     When the source file is compiled with ‘_FILE_OFFSET_BITS == 64’ on
     a 32 bits machine this function is actually available under the
     name ‘lseek’ and so transparently replaces the 32 bit interface.

   You can have multiple descriptors for the same file if you open the
file more than once, or if you duplicate a descriptor with ‘dup’.
Descriptors that come from separate calls to ‘open’ have independent
file positions; using ‘lseek’ on one descriptor has no effect on the
other.  For example,

     {
       int d1, d2;
       char buf[4];
       d1 = open ("foo", O_RDONLY);
       d2 = open ("foo", O_RDONLY);
       lseek (d1, 1024, SEEK_SET);
       read (d2, buf, 4);
     }

will read the first four characters of the file ‘foo’.  (The
error-checking code necessary for a real program has been omitted here
for brevity.)

   By contrast, descriptors made by duplication share a common file
position with the original descriptor that was duplicated.  Anything
which alters the file position of one of the duplicates, including
reading or writing data, affects all of them alike.  Thus, for example,

     {
       int d1, d2, d3;
       char buf1[4], buf2[4];
       d1 = open ("foo", O_RDONLY);
       d2 = dup (d1);
       d3 = dup (d2);
       lseek (d3, 1024, SEEK_SET);
       read (d1, buf1, 4);
       read (d2, buf2, 4);
     }

will read four characters starting with the 1024’th character of ‘foo’,
and then four more characters starting with the 1028’th character.

 -- Data Type: off_t

     This is a signed integer type used to represent file sizes.  In the
     GNU C Library, this type is no narrower than ‘int’.

     If the source is compiled with ‘_FILE_OFFSET_BITS == 64’ this type
     is transparently replaced by ‘off64_t’.

 -- Data Type: off64_t

     This type is used similar to ‘off_t’.  The difference is that even
     on 32 bit machines, where the ‘off_t’ type would have 32 bits,
     ‘off64_t’ has 64 bits and so is able to address files up to 2^63
     bytes in length.

     When compiling with ‘_FILE_OFFSET_BITS == 64’ this type is
     available under the name ‘off_t’.

   These aliases for the ‘SEEK_…’ constants exist for the sake of
compatibility with older BSD systems.  They are defined in two different
header files: ‘fcntl.h’ and ‘sys/file.h’.

‘L_SET’
     An alias for ‘SEEK_SET’.

‘L_INCR’
     An alias for ‘SEEK_CUR’.

‘L_XTND’
     An alias for ‘SEEK_END’.


File: libc.info,  Node: Descriptors and Streams,  Next: Stream/Descriptor Precautions,  Prev: File Position Primitive,  Up: Low-Level I/O

13.4 Descriptors and Streams
============================

Given an open file descriptor, you can create a stream for it with the
‘fdopen’ function.  You can get the underlying file descriptor for an
existing stream with the ‘fileno’ function.  These functions are
declared in the header file ‘stdio.h’.

 -- Function: FILE * fdopen (int FILEDES, const char *OPENTYPE)

     Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe mem lock |
     *Note POSIX Safety Concepts::.

     The ‘fdopen’ function returns a new stream for the file descriptor
     FILEDES.

     The OPENTYPE argument is interpreted in the same way as for the
     ‘fopen’ function (*note Opening Streams::), except that the ‘b’
     option is not permitted; this is because GNU systems make no
     distinction between text and binary files.  Also, ‘"w"’ and ‘"w+"’
     do not cause truncation of the file; these have an effect only when
     opening a file, and in this case the file has already been opened.
     You must make sure that the OPENTYPE argument matches the actual
     mode of the open file descriptor.

     The return value is the new stream.  If the stream cannot be
     created (for example, if the modes for the file indicated by the
     file descriptor do not permit the access specified by the OPENTYPE
     argument), a null pointer is returned instead.

     In some other systems, ‘fdopen’ may fail to detect that the modes
     for file descriptors do not permit the access specified by
     ‘opentype’.  The GNU C Library always checks for this.

   For an example showing the use of the ‘fdopen’ function, see *note
Creating a Pipe::.

 -- Function: int fileno (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function returns the file descriptor associated with the
     stream STREAM.  If an error is detected (for example, if the STREAM
     is not valid) or if STREAM does not do I/O to a file, ‘fileno’
     returns -1.

 -- Function: int fileno_unlocked (FILE *STREAM)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘fileno_unlocked’ function is equivalent to the ‘fileno’
     function except that it does not implicitly lock the stream if the
     state is ‘FSETLOCKING_INTERNAL’.

     This function is a GNU extension.

   There are also symbolic constants defined in ‘unistd.h’ for the file
descriptors belonging to the standard streams ‘stdin’, ‘stdout’, and
‘stderr’; see *note Standard Streams::.

‘STDIN_FILENO’

     This macro has value ‘0’, which is the file descriptor for standard
     input.

‘STDOUT_FILENO’

     This macro has value ‘1’, which is the file descriptor for standard
     output.

‘STDERR_FILENO’

     This macro has value ‘2’, which is the file descriptor for standard
     error output.


File: libc.info,  Node: Stream/Descriptor Precautions,  Next: Scatter-Gather,  Prev: Descriptors and Streams,  Up: Low-Level I/O

13.5 Dangers of Mixing Streams and Descriptors
==============================================

You can have multiple file descriptors and streams (let’s call both
streams and descriptors “channels” for short) connected to the same
file, but you must take care to avoid confusion between channels.  There
are two cases to consider: "linked" channels that share a single file
position value, and "independent" channels that have their own file
positions.

   It’s best to use just one channel in your program for actual data
transfer to any given file, except when all the access is for input.
For example, if you open a pipe (something you can only do at the file
descriptor level), either do all I/O with the descriptor, or construct a
stream from the descriptor with ‘fdopen’ and then do all I/O with the
stream.

* Menu:

* Linked Channels::	   Dealing with channels sharing a file position.
* Independent Channels::   Dealing with separately opened, unlinked channels.
* Cleaning Streams::	   Cleaning a stream makes it safe to use
                            another channel.


File: libc.info,  Node: Linked Channels,  Next: Independent Channels,  Up: Stream/Descriptor Precautions

13.5.1 Linked Channels
----------------------

Channels that come from a single opening share the same file position;
we call them "linked" channels.  Linked channels result when you make a
stream from a descriptor using ‘fdopen’, when you get a descriptor from
a stream with ‘fileno’, when you copy a descriptor with ‘dup’ or ‘dup2’,
and when descriptors are inherited during ‘fork’.  For files that don’t
support random access, such as terminals and pipes, _all_ channels are
effectively linked.  On random-access files, all append-type output
streams are effectively linked to each other.

   If you have been using a stream for I/O (or have just opened the
stream), and you want to do I/O using another channel (either a stream
or a descriptor) that is linked to it, you must first "clean up" the
stream that you have been using.  *Note Cleaning Streams::.

   Terminating a process, or executing a new program in the process,
destroys all the streams in the process.  If descriptors linked to these
streams persist in other processes, their file positions become
undefined as a result.  To prevent this, you must clean up the streams
before destroying them.

