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mbrtowc

Section: C Library Functions (3)
Updated: 202-0-08
Index Return to Main Contents

NAME

mbrtowc - convert a multibyte sequence to a wide character

LIBRARY

Standard C library (libc,~-lc)

SYNOPSIS

#include <wchar.h>
size_t mbrtowc(size_t n;
               wchar_t *restrict pwc, const char s[restrict n],
               size_t n, mbstate_t *restrict ps);

DESCRIPTION

The main case for this function is when s is not NULL and pwc is not NULL. In this case, the mbrtowc() 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 the shift state *ps. If the converted wide character is not L[aq][rs]0[aq] (the null wide character), it returns the number of bytes that were consumed from s. If the converted wide character is L[aq][rs]0[aq], it resets the shift state *ps to the initial state and returns 0. If the n bytes starting at s do not contain a complete multibyte character, mbrtowc() returns (size_t) -2. This can happen even if n >= MB_CUR_MAX, if the multibyte string contains redundant shift sequences. If the multibyte string starting at s contains an invalid multibyte sequence before the next complete character, mbrtowc() returns (size_t) -1 and sets errno to EILSEQ. In this case, the effects on *ps are undefined. A different case is when s is not NULL but pwc is NULL. In this case, the mbrtowc() 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, pwc and n are ignored. If the conversion state represented by *ps denotes an incomplete multibyte character conversion, the mbrtowc() function returns (size_t) -1, sets errno to EILSEQ, and leaves *ps in an undefined state. Otherwise, the mbrtowc() function puts *ps in the initial state and returns 0. In all of the above cases, if ps is NULL, a static anonymous state known only to the mbrtowc() function is used instead. Otherwise, *ps must be a valid mbstate_t object. An mbstate_t object a can be initialized to the initial state by zeroing it, for example using memset(&a, 0, sizeof(a));

RETURN VALUE

The mbrtowc() function returns the number of bytes parsed from the multibyte sequence starting at s, if a no-L[aq][rs]0[aq] wide character was recognized. It returns 0, if a L[aq][rs]0[aq] wide character was recognized. It returns (size_t) -1 and sets errno to EILSEQ, if an invalid multibyte sequence was encountered. It returns (size_t) -2 if the consumed n bytes form a valid partial character sequence; more subsequent data needs to be fed in.