mbtowc − convert a multibyte sequence to a wide character
int mbtowc (wchar_t *pwc, const char *s, size_t n);
The main case for this function is when s is not NULL and pwc is not NULL. In this case, the mbtowc function inspects at most n bytes of the multibyte string starting at s, extracts the next complete multibyte character, converts it to a wide character and stores it at *pwc. It updates an internal shift state only known to the mbtowc function. It s does not point to a ’\0’ byte, it returns the number of bytes that were consumed from s, otherwise it returns 0.
If the n bytes starting at s do not contain a complete multibyte character, or if they contain an invalid multibyte sequence, mbtowc returns -1. This can happen even if n >= MB_CUR_MAX, if the multibyte string contains redundant shift sequences.
A different case is when s is not NULL but pwc is NULL. In this case the mbtowc function behaves as above, excepts that it does not store the converted wide character in memory.
A third case is when s is NULL. In this case, pwc and n are ignored. The mbtowc function resets the shift state, only known to this function, to the initial state, and returns non-zero if the encoding has non-trivial shift state, or zero if the encoding is stateless.
If s is not NULL, the mbtowc function returns the number of consumed bytes starting at s, or 0 if s points to a null byte, or -1 upon failure.
If s is NULL, the mbtowc function returns non-zero if the encoding has non-trivial shift state, or zero if the encoding is stateless.
ISO/ANSI C, UNIX98
The behaviour of mbtowc depends on the LC_CTYPE category of the current locale.
This function is not multi-thread safe. The function mbrtowc provides a better interface to the same functionality.