mbtowc - convert a multibyte sequence to a wide character
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 known only to the mbtowc() function. If
s does not point to a null byte ('\0'), it returns the number of bytes that were consumed from
s, otherwise it returns 0.
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
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, except that it does not store the converted wide character in memory.
A third case is when
s is NULL. In this case,
n are ignored. The mbtowc() function resets the shift state, only known to this function, to the initial state, and returns nonzero if the encoding has nontrivial shift state, or zero if the encoding is stateless.
POSIX.1-2001, POSIX.1-2008, C99.
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