GNU libunistring: 14. Case mappings <unicase.h>

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# 14. Case mappings `<unicase.h>`

This include file defines functions for case mapping for Unicode strings and case insensitive comparison of Unicode strings and C strings.

These string functions fix the problems that were mentioned in ‘`char *`’ strings, namely, they handle the Croatian LETTER DZ WITH CARON, the German LATIN SMALL LETTER SHARP S, the Greek sigma and the Lithuanian i correctly.

## 14.1 Case mappings of characters

The following functions implement case mappings on Unicode characters — for those cases only where the result of the mapping is a again a single Unicode character.

These mappings are locale and context independent.

WARNING! These functions are not sufficient for languages such as German, Greek and Lithuanian. Better use the functions below that treat an entire string at once and are language aware.

Function: ucs4_t uc_toupper (ucs4_t uc)

  Returns the uppercase mapping of the Unicode character uc.

Function: ucs4_t uc_tolower (ucs4_t uc)

  Returns the lowercase mapping of the Unicode character uc.

Function: ucs4_t uc_totitle (ucs4_t uc)

  Returns the titlecase mapping of the Unicode character uc.

  The titlecase mapping of a character is to be used when the character should look like upper case and the following characters are lower cased.

  For most characters, this is the same as the uppercase mapping. There are only few characters where the title case variant and the upper case variant are different. These characters occur in the Latin writing of the Croatian, Bosnian, and Serbian languages.

  Lower case | Title case | Upper case
  --- | --- | ---
  LATIN SMALL LETTER LJ | LATIN CAPITAL LETTER L WITH SMALL LETTER J | LATIN CAPITAL LETTER LJ
  LATIN SMALL LETTER NJ | LATIN CAPITAL LETTER N WITH SMALL LETTER J | LATIN CAPITAL LETTER NJ
  LATIN SMALL LETTER DZ | LATIN CAPITAL LETTER D WITH SMALL LETTER Z | LATIN CAPITAL LETTER DZ
  LATIN SMALL LETTER DZ WITH CARON | LATIN CAPITAL LETTER D WITH SMALL LETTER Z WITH CARON | LATIN CAPITAL LETTER DZ WITH CARON

## 14.2 Case mappings of strings

Case mapping should always be performed on entire strings, not on individual characters. The functions in this section do so.

These functions allow to apply a normalization after the case mapping. The reason is that if you want to treat ‘`ä`’ and ‘`Ä`’ the same, you most often also want to treat the composed and decomposed forms of such a character, U+00C4 LATIN CAPITAL LETTER A WITH DIAERESIS and U+0041 LATIN CAPITAL LETTER A U+0308 COMBINING DIAERESIS the same. The nf argument designates the normalization.

These functions are locale dependent. The iso639_language argument identifies the language (e.g. `"tr"` for Turkish). NULL means to use locale independent case mappings.

Function: const char * uc_locale_language ()

  Returns the ISO 639 language code of the current locale. Returns `""` if it is unknown, or in the "C" locale.

Function: uint8_t * u8_toupper (const uint8_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint8_t *resultbuf, size_t *lengthp)
Function: uint16_t * u16_toupper (const uint16_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint16_t *resultbuf, size_t *lengthp)
Function: uint32_t * u32_toupper (const uint32_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint32_t *resultbuf, size_t *lengthp)

  Returns the uppercase mapping of a string.

  The nf argument identifies the normalization form to apply after the case-mapping. It can also be NULL, for no normalization.

  The resultbuf and lengthp arguments are as described in chapter Conventions.

Function: uint8_t * u8_tolower (const uint8_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint8_t *resultbuf, size_t *lengthp)
Function: uint16_t * u16_tolower (const uint16_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint16_t *resultbuf, size_t *lengthp)
Function: uint32_t * u32_tolower (const uint32_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint32_t *resultbuf, size_t *lengthp)

  Returns the lowercase mapping of a string.

  The nf argument identifies the normalization form to apply after the case-mapping. It can also be NULL, for no normalization.

  The resultbuf and lengthp arguments are as described in chapter Conventions.

Function: uint8_t * u8_totitle (const uint8_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint8_t *resultbuf, size_t *lengthp)
Function: uint16_t * u16_totitle (const uint16_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint16_t *resultbuf, size_t *lengthp)
Function: uint32_t * u32_totitle (const uint32_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint32_t *resultbuf, size_t *lengthp)

  Returns the titlecase mapping of a string.

  Mapping to title case means that, in each word, the first cased character is being mapped to title case and the remaining characters of the word are being mapped to lower case.

  The nf argument identifies the normalization form to apply after the case-mapping. It can also be NULL, for no normalization.

  The resultbuf and lengthp arguments are as described in chapter Conventions.

## 14.3 Case mappings of substrings

Case mapping of a substring cannot simply be performed by extracting the substring and then applying the case mapping function to it. This does not work because case mapping requires some information about the surrounding characters. The following functions allow to apply case mappings to substrings of a given string, while taking into account the characters that precede it (the “prefix”) and the characters that follow it (the “suffix”).

Type: casing_prefix_context_t

  This data type denotes the case-mapping context that is given by a prefix string. It is an immediate type that can be copied by simple assignment, without involving memory allocation. It is not an array type.

Constant: casing_prefix_context_t unicase_empty_prefix_context

  This constant is the case-mapping context that corresponds to an empty prefix string.

The following functions return `casing_prefix_context_t` objects:

Function: casing_prefix_context_t u8_casing_prefix_context (const uint8_t *s, size_t n)
Function: casing_prefix_context_t u16_casing_prefix_context (const uint16_t *s, size_t n)
Function: casing_prefix_context_t u32_casing_prefix_context (const uint32_t *s, size_t n)

  Returns the case-mapping context of a given prefix string.

Function: casing_prefix_context_t u8_casing_prefixes_context (const uint8_t *s, size_t n, casing_prefix_context_t a_context)
Function: casing_prefix_context_t u16_casing_prefixes_context (const uint16_t *s, size_t n, casing_prefix_context_t a_context)
Function: casing_prefix_context_t u32_casing_prefixes_context (const uint32_t *s, size_t n, casing_prefix_context_t a_context)

  Returns the case-mapping context of the prefix concat(a, s), given the case-mapping context of the prefix a.

Type: casing_suffix_context_t

  This data type denotes the case-mapping context that is given by a suffix string. It is an immediate type that can be copied by simple assignment, without involving memory allocation. It is not an array type.

Constant: casing_suffix_context_t unicase_empty_suffix_context

  This constant is the case-mapping context that corresponds to an empty suffix string.

The following functions return `casing_suffix_context_t` objects:

Function: casing_suffix_context_t u8_casing_suffix_context (const uint8_t *s, size_t n)
Function: casing_suffix_context_t u16_casing_suffix_context (const uint16_t *s, size_t n)
Function: casing_suffix_context_t u32_casing_suffix_context (const uint32_t *s, size_t n)

  Returns the case-mapping context of a given suffix string.

Function: casing_suffix_context_t u8_casing_suffixes_context (const uint8_t *s, size_t n, casing_suffix_context_t a_context)
Function: casing_suffix_context_t u16_casing_suffixes_context (const uint16_t *s, size_t n, casing_suffix_context_t a_context)
Function: casing_suffix_context_t u32_casing_suffixes_context (const uint32_t *s, size_t n, casing_suffix_context_t a_context)

  Returns the case-mapping context of the suffix concat(s, a), given the case-mapping context of the suffix a.

The following functions perform a case mapping, considering the prefix context and the suffix context.

Function: uint8_t * u8_ct_toupper (const uint8_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint8_t *resultbuf, size_t *lengthp)
Function: uint16_t * u16_ct_toupper (const uint16_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint16_t *resultbuf, size_t *lengthp)
Function: uint32_t * u32_ct_toupper (const uint32_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint32_t *resultbuf, size_t *lengthp)

  Returns the uppercase mapping of a string that is surrounded by a prefix and a suffix.

  The resultbuf and lengthp arguments are as described in chapter Conventions.

Function: uint8_t * u8_ct_tolower (const uint8_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint8_t *resultbuf, size_t *lengthp)
Function: uint16_t * u16_ct_tolower (const uint16_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint16_t *resultbuf, size_t *lengthp)
Function: uint32_t * u32_ct_tolower (const uint32_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint32_t *resultbuf, size_t *lengthp)

  Returns the lowercase mapping of a string that is surrounded by a prefix and a suffix.

  The resultbuf and lengthp arguments are as described in chapter Conventions.

Function: uint8_t * u8_ct_totitle (const uint8_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint8_t *resultbuf, size_t *lengthp)
Function: uint16_t * u16_ct_totitle (const uint16_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint16_t *resultbuf, size_t *lengthp)
Function: uint32_t * u32_ct_totitle (const uint32_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint32_t *resultbuf, size_t *lengthp)

  Returns the titlecase mapping of a string that is surrounded by a prefix and a suffix.

  The resultbuf and lengthp arguments are as described in chapter Conventions.

For example, to uppercase the UTF-8 substring between `s + start_index` and `s + end_index` of a string that extends from `s` to `s + u8_strlen (s)`, you can use the statements

    size_t result_length;
    uint8_t result =
      u8_ct_toupper (s + start_index, end_index - start_index,
                     u8_casing_prefix_context (s, start_index),
                     u8_casing_suffix_context (s + end_index,
                                               u8_strlen (s) - end_index),
                     iso639_language, NULL, NULL, &result_length);

## 14.4 Case insensitive comparison

The following functions implement comparison that ignores differences in case and normalization.

Function: uint8_t * u8_casefold (const uint8_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint8_t *resultbuf, size_t *lengthp)
Function: uint16_t * u16_casefold (const uint16_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint16_t *resultbuf, size_t *lengthp)
Function: uint32_t * u32_casefold (const uint32_t *s, size_t n, const char *iso639_language, uninorm_t nf, uint32_t *resultbuf, size_t *lengthp)

  Returns the case folded string.

  Comparing `u8_casefold (s1)` and `u8_casefold (s2)` with the `u8_cmp2` function is equivalent to comparing s1 and s2 with `u8_casecmp`.

  The nf argument identifies the normalization form to apply after the case-mapping. It can also be NULL, for no normalization.

  The resultbuf and lengthp arguments are as described in chapter Conventions.

Function: uint8_t * u8_ct_casefold (const uint8_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint8_t *resultbuf, size_t *lengthp)
Function: uint16_t * u16_ct_casefold (const uint16_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint16_t *resultbuf, size_t *lengthp)
Function: uint32_t * u32_ct_casefold (const uint32_t *s, size_t n, casing_prefix_context_t prefix_context, casing_suffix_context_t suffix_context, const char *iso639_language, uninorm_t nf, uint32_t *resultbuf, size_t *lengthp)

  Returns the case folded string. The case folding takes into account the case mapping contexts of the prefix and suffix strings.

  The resultbuf and lengthp arguments are as described in chapter Conventions.

The following functions ignore locale-dependent collation rules, but do use locale-dependent case mappings (if iso639_language is not NULL).

Function: int u8_casecmp (const uint8_t *s1, size_t n1, const uint8_t *s2, size_t n2, const char *iso639_language, uninorm_t nf, int *resultp)
Function: int u16_casecmp (const uint16_t *s1, size_t n1, const uint16_t *s2, size_t n2, const char *iso639_language, uninorm_t nf, int *resultp)
Function: int u32_casecmp (const uint32_t *s1, size_t n1, const uint32_t *s2, size_t n2, const char *iso639_language, uninorm_t nf, int *resultp)
Function: int ulc_casecmp (const char *s1, size_t n1, const char *s2, size_t n2, const char *iso639_language, uninorm_t nf, int *resultp)

  Compares s1 and s2, ignoring differences in case and normalization.

  The nf argument identifies the normalization form to apply after the case-mapping. It can also be NULL, for no normalization.

  If successful, sets `*resultp` to -1 if s1 < s2, 0 if s1 = s2, 1 if s1 > s2, and returns 0. Upon failure, returns -1 with `errno` set.

The following functions additionally take into account the sorting rules of the current locale.

Function: char * u8_casexfrm (const uint8_t *s, size_t n, const char *iso639_language, uninorm_t nf, char *resultbuf, size_t *lengthp)
Function: char * u16_casexfrm (const uint16_t *s, size_t n, const char *iso639_language, uninorm_t nf, char *resultbuf, size_t *lengthp)
Function: char * u32_casexfrm (const uint32_t *s, size_t n, const char *iso639_language, uninorm_t nf, char *resultbuf, size_t *lengthp)
Function: char * ulc_casexfrm (const char *s, size_t n, const char *iso639_language, uninorm_t nf, char *resultbuf, size_t *lengthp)

  Converts the string s of length n to a NUL-terminated byte sequence, in such a way that comparing `u8_casexfrm (s1)` and `u8_casexfrm (s2)` with the gnulib function `memcmp2` is equivalent to comparing s1 and s2 with `u8_casecoll`.

  nf must be either `UNINORM_NFC`, `UNINORM_NFKC`, or NULL for no normalization.

  The resultbuf and lengthp arguments are as described in chapter Conventions.

Function: int u8_casecoll (const uint8_t *s1, size_t n1, const uint8_t *s2, size_t n2, const char *iso639_language, uninorm_t nf, int *resultp)
Function: int u16_casecoll (const uint16_t *s1, size_t n1, const uint16_t *s2, size_t n2, const char *iso639_language, uninorm_t nf, int *resultp)
Function: int u32_casecoll (const uint32_t *s1, size_t n1, const uint32_t *s2, size_t n2, const char *iso639_language, uninorm_t nf, int *resultp)
Function: int ulc_casecoll (const char *s1, size_t n1, const char *s2, size_t n2, const char *iso639_language, uninorm_t nf, int *resultp)

  Compares s1 and s2, ignoring differences in case and normalization, using the collation rules of the current locale.

  The nf argument identifies the normalization form to apply after the case-mapping. It must be either `UNINORM_NFC` or `UNINORM_NFKC`. It can also be NULL, for no normalization.

  If successful, sets `*resultp` to -1 if s1 < s2, 0 if s1 = s2, 1 if s1 > s2, and returns 0. Upon failure, returns -1 with `errno` set.

## 14.5 Case detection

The following functions determine whether a Unicode string is entirely in upper case. or entirely in lower case, or entirely in title case, or already case-folded.

Function: int u8_is_uppercase (const uint8_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u16_is_uppercase (const uint16_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u32_is_uppercase (const uint32_t *s, size_t n, const char *iso639_language, bool *resultp)

  Sets `*resultp` to true if mapping NFD(s) to upper case is a no-op, or to false otherwise, and returns 0. Upon failure, returns -1 with `errno` set.

Function: int u8_is_lowercase (const uint8_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u16_is_lowercase (const uint16_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u32_is_lowercase (const uint32_t *s, size_t n, const char *iso639_language, bool *resultp)

  Sets `*resultp` to true if mapping NFD(s) to lower case is a no-op, or to false otherwise, and returns 0. Upon failure, returns -1 with `errno` set.

Function: int u8_is_titlecase (const uint8_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u16_is_titlecase (const uint16_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u32_is_titlecase (const uint32_t *s, size_t n, const char *iso639_language, bool *resultp)

  Sets `*resultp` to true if mapping NFD(s) to title case is a no-op, or to false otherwise, and returns 0. Upon failure, returns -1 with `errno` set.

Function: int u8_is_casefolded (const uint8_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u16_is_casefolded (const uint16_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u32_is_casefolded (const uint32_t *s, size_t n, const char *iso639_language, bool *resultp)

  Sets `*resultp` to true if applying case folding to NFD(S) is a no-op, or to false otherwise, and returns 0. Upon failure, returns -1 with `errno` set.

The following functions determine whether case mappings have any effect on a Unicode string.

Function: int u8_is_cased (const uint8_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u16_is_cased (const uint16_t *s, size_t n, const char *iso639_language, bool *resultp)
Function: int u32_is_cased (const uint32_t *s, size_t n, const char *iso639_language, bool *resultp)

  Sets `*resultp` to true if case matters for s, that is, if mapping NFD(s) to either upper case or lower case or title case is not a no-op. Set `*resultp` to false if NFD(s) maps to itself under the upper case mapping, under the lower case mapping, and under the title case mapping; in other words, when NFD(s) consists entirely of caseless characters. Upon failure, returns -1 with `errno` set.

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