setjmp(3avr)

NAME
setjmp - <setjmp.h>: Non-local goto

SYNOPSIS

  Functions
int setjmp (jmp_buf __jmpb)
void longjmp (jmp_buf __jmpb, int __ret) __ATTR_NORETURN__

Detailed Description

While the C language has the dreaded goto statement, it can only be used to jump to a label in the same (local) function. In order to jump directly to another (non-local) function, the C library provides the setjmp() and longjmp() functions. setjmp() and longjmp() are useful for dealing with errors and interrupts encountered in a low-level subroutine of a program.

Note
    setjmp() and longjmp() make programs hard to understand and maintain. If possible, an alternative should be used.

    longjmp() can destroy changes made to global register variables (see How to permanently bind a variable to a register?).

For a very detailed discussion of setjmp()/longjmp(), see Chapter 7 of Advanced Programming in the UNIX Environment, by W. Richard Stevens.

Example:

#include <setjmp.h>
jmp_buf env;
int main (void)
{
    if (setjmp (env))
    {
        ... handle error ...
    }
    while (1)
    {
       ... main processing loop which calls foo() some where ...
    }
}
...
void foo (void)
{
    ... blah, blah, blah ...
    if (err)
    {
        longjmp (env, 1);
    }
}

Function Documentation

  void longjmp (jmp_buf __jmpb, int __ret)

Non-local jump to a saved stack context.

#include <setjmp.h>

longjmp() restores the environment saved by the last call of setjmp() with the corresponding __jmpb argument. After longjmp() is completed, program execution continues as if the corresponding call of setjmp() had just returned the value __ret.

Note
    longjmp() cannot cause 0 to be returned. If longjmp() is invoked with a second argument of 0, 1 will be returned instead.

Parameters
    __jmpb Information saved by a previous call to setjmp().
    __ret Value to return to the caller of setjmp().

Returns
    This function never returns.

  int setjmp (jmp_buf __jmpb)

Save stack context for non-local goto.

#include <setjmp.h>

setjmp() saves the stack context/environment in __jmpb for later use by longjmp(). The stack context will be invalidated if the function which called setjmp() returns.

Parameters
    __jmpb Variable of type jmp_buf which holds the stack information such that the environment can be restored.

Returns
    setjmp() returns 0 if returning directly, and non-zero when returning from longjmp() using the saved context.

Author

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