MBRTOWC(3) Library Functions Manual MBRTOWC(3)

mbrtowc — converts a multibyte character to a wide character (restartable)

Standard C Library (libc, -lc)

#include <wchar.h>

size_t
mbrtowc(wchar_t * restrict pwc, const char * restrict s, size_t n, mbstate_t * restrict ps);

The () usually converts the multibyte character pointed to by s to a wide character, and stores the wide character to the wchar_t object pointed to by pwc if pwc is non-NULL and s points to a valid character. The conversion happens in accordance with, and changes the conversion state described in the mbstate_t object pointed to by ps. This function may examine at most n bytes of the array beginning from s.

If s points to a valid character and the character corresponds to a nul wide character, then the () places the mbstate_t object pointed to by ps to an initial conversion state.

Unlike mbtowc(3), the () may accept the byte sequence pointed to by s not forming a complete multibyte character but which may be part of a valid character. In this case, this function will accept all such bytes and save them into the conversion state object pointed to by ps. They will be used at subsequent calls of this function to restart the conversion suspended.

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

These are the special cases:

s == NULL
() sets the conversion state object pointed to by ps to an initial state and always returns 0. Unlike mbtowc(3), the value returned does not indicate whether the current encoding of the locale is state-dependent.

In this case, () ignores pwc and n, and is equivalent to the following call:

mbrtowc(NULL, "", 1, ps);
pwc == NULL
The conversion from a multibyte character to a wide character has taken place and the conversion state may be affected, but the resulting wide character is discarded.
ps == NULL
mbrtowc() uses its own internal state object to keep the conversion state, instead of ps mentioned in this manual page.

Calling any other functions in Standard C Library (libc, -lc) never changes the internal state of (), which is initialized at startup time of the program.

In the usual cases, mbrtowc() returns:

0
The next bytes pointed to by s form a nul character.
positive
If s points to a valid character, mbrtowc() returns the number of bytes in the character.
(size_t)-2
s points to a byte sequence which possibly contains part of a valid multibyte character, but which is incomplete. When n is at least MB_CUR_MAX, this case can only occur if the array pointed to by s contains a redundant shift sequence.
(size_t)-1
s points to an illegal byte sequence which does not form a valid multibyte character. In this case, mbrtowc() sets errno to indicate the error.

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

[]
s points to an invalid or incomplete multibyte character.
[]
ps points to an invalid or uninitialized mbstate_t object.

mbrlen(3), mbtowc(3), setlocale(3)

The mbrtowc() function conforms to ISO/IEC 9899/AMD1:1995 (“ISO C90, Amendment 1”). The restrict qualifier is added at ISO/IEC 9899:1999 (“ISO C99”).

February 4, 2002 NetBSD 11.0