MBTOWC(3)

NAME
mbtowc - converts a multibyte character to a wide character

LIBRARY
libc

SYNOPSIS
#include <stdlib.h>
int
mbtowc(wchar_t * restrict pwc, const char * restrict s, size_t n);

DESCRIPTION
mbtowc() usually converts the multibyte character pointed to by s to a wide character, and stores it in the wchar_t object pointed to by pwc if pwc is non-NULL and s points to a valid character. This function may inspect at most n bytes of the array beginning from s.

In state-dependent encodings, s may point to the special sequence bytes to change the shift-state. Although such sequence bytes correspond to no individual wide-character code, mbtowc() changes its own state by the sequence bytes and treats them as if they are a part of the subsequence multibyte character.

Unlike mbrtowc(3), the first n bytes pointed to by s need to form an entire multibyte character. Otherwise, this function causes an error.

Calling any other functions in libc never changes the internal state of mbtowc(), except for calling setlocale(3) with changing the LC_CTYPE category of the current locale. Such setlocale(3) call causes the internal state of this function to be indeterminate.

The behaviour of mbtowc() is affected by the LC_CTYPE category of the current locale.

There are special cases:

s == NULL
    mbtowc() initializes its own internal state to an initial state, and determines whether the current encoding is state-dependent. This function returns 0 if the encoding is state-independent, otherwise non-zero. In this case, pwc is completely ignored.

pwc == NULL
    mbtowc() executes the conversion as if pwc is non-NULL, but a result of the conversion is discarded.

n == 0
    In this case, the first n bytes of the array pointed to by s never form a complete character. Thus, the mbtowc() always fails.

RETURN VALUES
Normally, the mbtowc() returns:

0   s points to a nul byte (‘\0’).

positive
    Number of bytes for the valid multibyte character pointed to by s. There are no cases that the value returned is greater than the value of the MB_CUR_MAX macro.

-1  s points to an invalid or an incomplete multibyte character. The mbtowc() also sets errno to indicate the error.

When s is equal to NULL, mbtowc() returns:

0   The current encoding is state-independent.

non-zero
    The current encoding is state-dependent.

ERRORS
mbtowc() may cause an error in the following case:

[EILSEQ]
    s points to an invalid or incomplete multibyte character.

SEE ALSO
mblen(3), mbrtowc(3), setlocale(3)

STANDARDS
The mbtowc() function conforms to ansiC. The restrict qualifier is added at isoC-99.