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# 4. Elementary Unicode string functions `<unistr.h>`

This include file declares elementary functions for Unicode strings. It is essentially the equivalent of what `<string.h>` is for C strings.

## 4.1 Elementary string checks

The following function is available to verify the integrity of a Unicode string.

Function: const uint8_t * u8_check (const uint8_t *s, size_t n)
Function: const uint16_t * u16_check (const uint16_t *s, size_t n)
Function: const uint32_t * u32_check (const uint32_t *s, size_t n)

  This function checks whether a Unicode string is well-formed. It returns NULL if valid, or a pointer to the first invalid unit otherwise.

## 4.2 Elementary string conversions

The following functions perform conversions between the different forms of Unicode strings.

Function: uint16_t * u8_to_u16 (const uint8_t *s, size_t n, uint16_t *resultbuf, size_t *lengthp)

  Converts an UTF-8 string to an UTF-16 string.

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

Function: uint32_t * u8_to_u32 (const uint8_t *s, size_t n, uint32_t *resultbuf, size_t *lengthp)

  Converts an UTF-8 string to an UTF-32 string.

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

Function: uint8_t * u16_to_u8 (const uint16_t *s, size_t n, uint8_t *resultbuf, size_t *lengthp)

  Converts an UTF-16 string to an UTF-8 string.

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

Function: uint32_t * u16_to_u32 (const uint16_t *s, size_t n, uint32_t *resultbuf, size_t *lengthp)

  Converts an UTF-16 string to an UTF-32 string.

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

Function: uint8_t * u32_to_u8 (const uint32_t *s, size_t n, uint8_t *resultbuf, size_t *lengthp)

  Converts an UTF-32 string to an UTF-8 string.

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

Function: uint16_t * u32_to_u16 (const uint32_t *s, size_t n, uint16_t *resultbuf, size_t *lengthp)

  Converts an UTF-32 string to an UTF-16 string.

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

## 4.3 Elementary string functions

### 4.3.1 Iterating over a Unicode string

The following functions inspect and return details about the first character in a Unicode string.

Function: int u8_mblen (const uint8_t *s, size_t n)
Function: int u16_mblen (const uint16_t *s, size_t n)
Function: int u32_mblen (const uint32_t *s, size_t n)

  Returns the length (number of units) of the first character in s, which is no longer than n. Returns 0 if it is the NUL character. Returns -1 upon failure.

  This function is similar to `mblen`, except that it operates on a Unicode string and that s must not be NULL.

Function: int u8_mbtouc (ucs4_t *puc, const uint8_t *s, size_t n)
Function: int u16_mbtouc (ucs4_t *puc, const uint16_t *s, size_t n)
Function: int u32_mbtouc (ucs4_t *puc, const uint32_t *s, size_t n)

  Returns the length (number of units) of the first character in s, putting its `ucs4_t` representation in `*puc`. Upon failure, `*puc` is set to `0xfffd`, and an appropriate number of units is returned.

  The number of available units, n, must be > 0.

  This function fails if an invalid sequence of units is encountered at the beginning of s, or if additional units (after the n provided units) would be needed to form a character.

  This function is similar to `mbtowc`, except that it operates on a Unicode string, puc and s must not be NULL, n must be > 0, and the NUL character is not treated specially.

Function: int u8_mbtouc_unsafe (ucs4_t *puc, const uint8_t *s, size_t n)
Function: int u16_mbtouc_unsafe (ucs4_t *puc, const uint16_t *s, size_t n)
Function: int u32_mbtouc_unsafe (ucs4_t *puc, const uint32_t *s, size_t n)

  This function is identical to `u8_mbtouc`/`u16_mbtouc`/`u32_mbtouc`. Earlier versions of this function performed fewer range-checks on the sequence of units.

Function: int u8_mbtoucr (ucs4_t *puc, const uint8_t *s, size_t n)
Function: int u16_mbtoucr (ucs4_t *puc, const uint16_t *s, size_t n)
Function: int u32_mbtoucr (ucs4_t *puc, const uint32_t *s, size_t n)

  Returns the length (number of units) of the first character in s, putting its `ucs4_t` representation in `*puc`. Upon failure, `*puc` is set to `0xfffd`, and -1 is returned for an invalid sequence of units, -2 is returned for an incomplete sequence of units.

  The number of available units, n, must be > 0.

  This function is similar to `u8_mbtouc`, except that the return value gives more details about the failure, similar to `mbrtowc`.

### 4.3.2 Creating Unicode strings one character at a time

The following function stores a Unicode character as a Unicode string in memory.

Function: int u8_uctomb (uint8_t *s, ucs4_t uc, ptrdiff_t n)
Function: int u16_uctomb (uint16_t *s, ucs4_t uc, ptrdiff_t n)
Function: int u32_uctomb (uint32_t *s, ucs4_t uc, ptrdiff_t n)

  Puts the multibyte character represented by uc in s, returning its length. Returns -1 upon failure, -2 if the number of available units, n, is too small. The latter case cannot occur if n >= 6/2/1, respectively.

  This function is similar to `wctomb`, except that it operates on a Unicode strings, s must not be NULL, and the argument n must be specified.

### 4.3.3 Copying Unicode strings

The following functions copy Unicode strings in memory.

Function: uint8_t * u8_cpy (uint8_t *dest, const uint8_t *src, size_t n)
Function: uint16_t * u16_cpy (uint16_t *dest, const uint16_t *src, size_t n)
Function: uint32_t * u32_cpy (uint32_t *dest, const uint32_t *src, size_t n)

  Copies n units from src to dest.

  This function is similar to `memcpy`, except that it operates on Unicode strings.

Function: uint8_t * u8_pcpy (uint8_t *dest, const uint8_t *src, size_t n)
Function: uint16_t * u16_pcpy (uint16_t *dest, const uint16_t *src, size_t n)
Function: uint32_t * u32_pcpy (uint32_t *dest, const uint32_t *src, size_t n)

  Copies n units from src to dest, returning a pointer after the last written unit.

  This function is similar to `mempcpy`, except that it operates on Unicode strings.

Function: uint8_t * u8_move (uint8_t *dest, const uint8_t *src, size_t n)
Function: uint16_t * u16_move (uint16_t *dest, const uint16_t *src, size_t n)
Function: uint32_t * u32_move (uint32_t *dest, const uint32_t *src, size_t n)

  Copies n units from src to dest, guaranteeing correct behavior for overlapping memory areas.

  This function is similar to `memmove`, except that it operates on Unicode strings.

The following function fills a Unicode string.

Function: uint8_t * u8_set (uint8_t *s, ucs4_t uc, size_t n)
Function: uint16_t * u16_set (uint16_t *s, ucs4_t uc, size_t n)
Function: uint32_t * u32_set (uint32_t *s, ucs4_t uc, size_t n)

  Sets the first n characters of s to uc. uc should be a character that occupies only 1 unit.

  This function is similar to `memset`, except that it operates on Unicode strings.

### 4.3.4 Comparing Unicode strings

The following function compares two Unicode strings of the same length.

Function: int u8_cmp (const uint8_t *s1, const uint8_t *s2, size_t n)
Function: int u16_cmp (const uint16_t *s1, const uint16_t *s2, size_t n)
Function: int u32_cmp (const uint32_t *s1, const uint32_t *s2, size_t n)

  Compares s1 and s2, each of length n, lexicographically. Returns a negative value if s1 compares smaller than s2, a positive value if s1 compares larger than s2, or 0 if they compare equal.

  This function is similar to `memcmp`, except that it operates on Unicode strings.

The following function compares two Unicode strings of possibly different lengths.

Function: int u8_cmp2 (const uint8_t *s1, size_t n1, const uint8_t *s2, size_t n2)
Function: int u16_cmp2 (const uint16_t *s1, size_t n1, const uint16_t *s2, size_t n2)
Function: int u32_cmp2 (const uint32_t *s1, size_t n1, const uint32_t *s2, size_t n2)

  Compares s1 and s2, lexicographically. Returns a negative value if s1 compares smaller than s2, a positive value if s1 compares larger than s2, or 0 if they compare equal.

  This function is similar to the gnulib function `memcmp2`, except that it operates on Unicode strings.

### 4.3.5 Searching for a character in a Unicode string

The following function searches for a given Unicode character.

Function: uint8_t * u8_chr (const uint8_t *s, size_t n, ucs4_t uc)
Function: uint16_t * u16_chr (const uint16_t *s, size_t n, ucs4_t uc)
Function: uint32_t * u32_chr (const uint32_t *s, size_t n, ucs4_t uc)

  Searches the string at s for uc. Returns a pointer to the first occurrence of uc in s, or NULL if uc does not occur in s.

  This function is similar to `memchr`, except that it operates on Unicode strings.

### 4.3.6 Counting the characters in a Unicode string

The following function counts the number of Unicode characters.

Function: size_t u8_mbsnlen (const uint8_t *s, size_t n)
Function: size_t u16_mbsnlen (const uint16_t *s, size_t n)
Function: size_t u32_mbsnlen (const uint32_t *s, size_t n)

  Counts and returns the number of Unicode characters in the n units from s.

  This function is similar to the gnulib function `mbsnlen`, except that it operates on Unicode strings.

## 4.4 Elementary string functions with memory allocation

The following function copies a Unicode string.

Function: uint8_t * u8_cpy_alloc (const uint8_t *s, size_t n)
Function: uint16_t * u16_cpy_alloc (const uint16_t *s, size_t n)
Function: uint32_t * u32_cpy_alloc (const uint32_t *s, size_t n)

  Makes a freshly allocated copy of s, of length n.

## 4.5 Elementary string functions on NUL terminated strings

### 4.5.1 Iterating over a NUL terminated Unicode string

The following functions inspect and return details about the first character in a Unicode string.

Function: int u8_strmblen (const uint8_t *s)
Function: int u16_strmblen (const uint16_t *s)
Function: int u32_strmblen (const uint32_t *s)

  Returns the length (number of units) of the first character in s. Returns 0 if it is the NUL character. Returns -1 upon failure.

Function: int u8_strmbtouc (ucs4_t *puc, const uint8_t *s)
Function: int u16_strmbtouc (ucs4_t *puc, const uint16_t *s)
Function: int u32_strmbtouc (ucs4_t *puc, const uint32_t *s)

  Returns the length (number of units) of the first character in s, putting its `ucs4_t` representation in `*puc`. Returns 0 if it is the NUL character. Returns -1 upon failure.

Function: const uint8_t * u8_next (ucs4_t *puc, const uint8_t *s)
Function: const uint16_t * u16_next (ucs4_t *puc, const uint16_t *s)
Function: const uint32_t * u32_next (ucs4_t *puc, const uint32_t *s)

  Forward iteration step. Advances the pointer past the next character, or returns NULL if the end of the string has been reached. Puts the character's `ucs4_t` representation in `*puc`.

The following function inspects and returns details about the previous character in a Unicode string.

Function: const uint8_t * u8_prev (ucs4_t *puc, const uint8_t *s, const uint8_t *start)
Function: const uint16_t * u16_prev (ucs4_t *puc, const uint16_t *s, const uint16_t *start)
Function: const uint32_t * u32_prev (ucs4_t *puc, const uint32_t *s, const uint32_t *start)

  Backward iteration step. Advances the pointer to point to the previous character (the one that ends at `s`), or returns NULL if the beginning of the string (specified by `start`) had been reached. Puts the character's `ucs4_t` representation in `*puc`. Note that this function works only on well-formed Unicode strings.

### 4.5.2 Length of a NUL terminated Unicode string

The following functions determine the length of a Unicode string.

Function: size_t u8_strlen (const uint8_t *s)
Function: size_t u16_strlen (const uint16_t *s)
Function: size_t u32_strlen (const uint32_t *s)

  Returns the number of units in s.

  This function is similar to `strlen` and `wcslen`, except that it operates on Unicode strings.

Function: size_t u8_strnlen (const uint8_t *s, size_t maxlen)
Function: size_t u16_strnlen (const uint16_t *s, size_t maxlen)
Function: size_t u32_strnlen (const uint32_t *s, size_t maxlen)

  Returns the number of units in s, but at most maxlen.

  This function is similar to `strnlen` and `wcsnlen`, except that it operates on Unicode strings.

### 4.5.3 Copying a NUL terminated Unicode string

The following functions copy portions of Unicode strings in memory.

Function: uint8_t * u8_strcpy (uint8_t *dest, const uint8_t *src)
Function: uint16_t * u16_strcpy (uint16_t *dest, const uint16_t *src)
Function: uint32_t * u32_strcpy (uint32_t *dest, const uint32_t *src)

  Copies src to dest.

  This function is similar to `strcpy` and `wcscpy`, except that it operates on Unicode strings.

Function: uint8_t * u8_stpcpy (uint8_t *dest, const uint8_t *src)
Function: uint16_t * u16_stpcpy (uint16_t *dest, const uint16_t *src)
Function: uint32_t * u32_stpcpy (uint32_t *dest, const uint32_t *src)

  Copies src to dest, returning the address of the terminating NUL in dest.

  This function is similar to `stpcpy`, except that it operates on Unicode strings.

Function: uint8_t * u8_strncpy (uint8_t *dest, const uint8_t *src, size_t n)
Function: uint16_t * u16_strncpy (uint16_t *dest, const uint16_t *src, size_t n)
Function: uint32_t * u32_strncpy (uint32_t *dest, const uint32_t *src, size_t n)

  Copies no more than n units of src to dest.

  This function is similar to `strncpy` and `wcsncpy`, except that it operates on Unicode strings.

Function: uint8_t * u8_stpncpy (uint8_t *dest, const uint8_t *src, size_t n)
Function: uint16_t * u16_stpncpy (uint16_t *dest, const uint16_t *src, size_t n)
Function: uint32_t * u32_stpncpy (uint32_t *dest, const uint32_t *src, size_t n)

  Copies no more than n units of src to dest. Returns a pointer past the last non-NUL unit written into dest. In other words, if the units written into dest include a NUL, the return value is the address of the first such NUL unit, otherwise it is `dest + n`.

  This function is similar to `stpncpy`, except that it operates on Unicode strings.

Function: uint8_t * u8_strcat (uint8_t *dest, const uint8_t *src)
Function: uint16_t * u16_strcat (uint16_t *dest, const uint16_t *src)
Function: uint32_t * u32_strcat (uint32_t *dest, const uint32_t *src)

  Appends src onto dest.

  This function is similar to `strcat` and `wcscat`, except that it operates on Unicode strings.

Function: uint8_t * u8_strncat (uint8_t *dest, const uint8_t *src, size_t n)
Function: uint16_t * u16_strncat (uint16_t *dest, const uint16_t *src, size_t n)
Function: uint32_t * u32_strncat (uint32_t *dest, const uint32_t *src, size_t n)

  Appends no more than n units of src onto dest.

  This function is similar to `strncat` and `wcsncat`, except that it operates on Unicode strings.

### 4.5.4 Comparing NUL terminated Unicode strings

The following functions compare two Unicode strings. They ignore locale-dependent collation rules.

Function: int u8_strcmp (const uint8_t *s1, const uint8_t *s2)
Function: int u16_strcmp (const uint16_t *s1, const uint16_t *s2)
Function: int u32_strcmp (const uint32_t *s1, const uint32_t *s2)

  Compares s1 and s2, lexicographically. Returns a negative value if s1 compares smaller than s2, a positive value if s1 compares larger than s2, or 0 if they compare equal.

  This function is similar to `strcmp` and `wcscmp`, except that it operates on Unicode strings.

Function: int u8_strcoll (const uint8_t *s1, const uint8_t *s2)
Function: int u16_strcoll (const uint16_t *s1, const uint16_t *s2)
Function: int u32_strcoll (const uint32_t *s1, const uint32_t *s2)

  Compares s1 and s2 using the collation rules of the current locale. Returns -1 if s1 < s2, 0 if s1 = s2, 1 if s1 > s2. Upon failure, sets `errno` and returns any value.

  This function is similar to `strcoll` and `wcscoll`, except that it operates on Unicode strings.

  Note that this function may consider different canonical normalizations of the same string as having a large distance. It is therefore better to use the function `u8_normcoll` instead of this one; see Normalization forms (composition and decomposition) `<uninorm.h>`.

Function: int u8_strncmp (const uint8_t *s1, const uint8_t *s2, size_t n)
Function: int u16_strncmp (const uint16_t *s1, const uint16_t *s2, size_t n)
Function: int u32_strncmp (const uint32_t *s1, const uint32_t *s2, size_t n)

  Compares no more than n units of s1 and s2.

  This function is similar to `strncmp` and `wcsncmp`, except that it operates on Unicode strings.

### 4.5.5 Duplicating a NUL terminated Unicode string

The following function allocates a duplicate of a Unicode string.

Function: uint8_t * u8_strdup (const uint8_t *s)
Function: uint16_t * u16_strdup (const uint16_t *s)
Function: uint32_t * u32_strdup (const uint32_t *s)

  Duplicates s, returning an identical malloc'd string.

  This function is similar to `strdup` and `wcsdup`, except that it operates on Unicode strings.

### 4.5.6 Searching for a character in a NUL terminated Unicode string

The following functions search for a given Unicode character.

Function: uint8_t * u8_strchr (const uint8_t *str, ucs4_t uc)
Function: uint16_t * u16_strchr (const uint16_t *str, ucs4_t uc)
Function: uint32_t * u32_strchr (const uint32_t *str, ucs4_t uc)

  Finds the first occurrence of uc in str.

  This function is similar to `strchr` and `wcschr`, except that it operates on Unicode strings.

Function: uint8_t * u8_strrchr (const uint8_t *str, ucs4_t uc)
Function: uint16_t * u16_strrchr (const uint16_t *str, ucs4_t uc)
Function: uint32_t * u32_strrchr (const uint32_t *str, ucs4_t uc)

  Finds the last occurrence of uc in str.

  This function is similar to `strrchr` and `wcsrchr`, except that it operates on Unicode strings.

The following functions search for the first occurrence of some Unicode character in or outside a given set of Unicode characters.

Function: size_t u8_strcspn (const uint8_t *str, const uint8_t *reject)
Function: size_t u16_strcspn (const uint16_t *str, const uint16_t *reject)
Function: size_t u32_strcspn (const uint32_t *str, const uint32_t *reject)

  Returns the length of the initial segment of str which consists entirely of Unicode characters not in reject.

  This function is similar to `strcspn` and `wcscspn`, except that it operates on Unicode strings.

Function: size_t u8_strspn (const uint8_t *str, const uint8_t *accept)
Function: size_t u16_strspn (const uint16_t *str, const uint16_t *accept)
Function: size_t u32_strspn (const uint32_t *str, const uint32_t *accept)

  Returns the length of the initial segment of str which consists entirely of Unicode characters in accept.

  This function is similar to `strspn` and `wcsspn`, except that it operates on Unicode strings.

Function: uint8_t * u8_strpbrk (const uint8_t *str, const uint8_t *accept)
Function: uint16_t * u16_strpbrk (const uint16_t *str, const uint16_t *accept)
Function: uint32_t * u32_strpbrk (const uint32_t *str, const uint32_t *accept)

  Finds the first occurrence in str of any character in accept.

  This function is similar to `strpbrk` and `wcspbrk`, except that it operates on Unicode strings.

### 4.5.7 Searching for a substring in a NUL terminated Unicode string

The following functions search whether a given Unicode string is a substring of another Unicode string.

Function: uint8_t * u8_strstr (const uint8_t *haystack, const uint8_t *needle)
Function: uint16_t * u16_strstr (const uint16_t *haystack, const uint16_t *needle)
Function: uint32_t * u32_strstr (const uint32_t *haystack, const uint32_t *needle)

  Finds the first occurrence of needle in haystack.

  This function is similar to `strstr` and `wcsstr`, except that it operates on Unicode strings.

Function: bool u8_startswith (const uint8_t *str, const uint8_t *prefix)
Function: bool u16_startswith (const uint16_t *str, const uint16_t *prefix)
Function: bool u32_startswith (const uint32_t *str, const uint32_t *prefix)

  Tests whether str starts with prefix.

Function: bool u8_endswith (const uint8_t *str, const uint8_t *suffix)
Function: bool u16_endswith (const uint16_t *str, const uint16_t *suffix)
Function: bool u32_endswith (const uint32_t *str, const uint32_t *suffix)

  Tests whether str ends with suffix.

### 4.5.8 Tokenizing a NUL terminated Unicode string

The following function does one step in tokenizing a Unicode string.

Function: uint8_t * u8_strtok (uint8_t *str, const uint8_t *delim, uint8_t **ptr)
Function: uint16_t * u16_strtok (uint16_t *str, const uint16_t *delim, uint16_t **ptr)
Function: uint32_t * u32_strtok (uint32_t *str, const uint32_t *delim, uint32_t **ptr)

  Divides str into tokens separated by characters in delim.

  This function is similar to `strtok_r` and `wcstok`, except that it operates on Unicode strings. Its interface is actually more similar to `wcstok` than to `strtok`.

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