MBTOWC(3)

NAME
mbtowc - converts a multibyte character to a wide character

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

DESCRIPTION
The 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 change the internal state of the mbtowc(), except for calling setlocale(3) with the LC_CTYPE category changed to that of the current locale. Such setlocale(3) calls cause the internal state of this function to be indeterminate.

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

These are the 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, mbtowc() returns:

0   s points to a null byte (‘\0’).

positive
    Number of bytes for the valid multibyte character pointed to by s. There are no cases where 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 cases:

[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 ISO/IEC 9899/1999 (“ISO C99”).

CAVEATS
On error, callers of mbtowc() cannot tell whether the multibyte character was invalid or incomplete. To treat incomplete data differently from invalid data the mbrtowc(3) function can be used instead.