MBTOWC(3) Library Functions Manual MBTOWC(3)

mbtowc — converts a multibyte character to a wide character

Standard C Library (libc, -lc)

#include <stdlib.h>

int
mbtowc(wchar_t * restrict pwc, const char * restrict s, size_t n);

() 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, () 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 Standard C Library (libc, -lc) never changes the internal state of (), 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 () is affected by the LC_CTYPE category of the current locale.

There are special cases:

s == NULL
() 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.

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.

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

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

mblen(3), mbrtowc(3), setlocale(3)

The mbtowc() function conforms to ANSI X3.159-1989 (“ANSI C89”). The restrict qualifier is added at ISO/IEC 9899:1999 (“ISO C99”).

February 3, 2002 NetBSD 11.0