2.27 mblen—minimal multibyte length function

Synopsis

#include <stdlib.h>
int mblen(const char *s, size_t n);

Description
When _MB_CAPABLE is not defined, this is a minimal ANSI-conforming implementation of mblen. In this case, the only “multi-byte character sequences” recognized are single bytes, and thus 1 is returned unless s is the null pointer or has a length of 0 or is the empty string.

When _MB_CAPABLE is defined, this routine calls _mbtowc_r to perform the conversion, passing a state variable to allow state dependent decoding. The result is based on the locale setting which may be restricted to a defined set of locales.

Returns
This implementation of mblen returns 0 if s is NULL or the empty string; it returns 1 if not _MB_CAPABLE or the character is a single-byte character; it returns -1 if the multi-byte character is invalid; otherwise it returns the number of bytes in the multibyte character.

Portability
mblen is required in the ANSI C standard. However, the precise effects vary with the locale.

mblen requires no supporting OS subroutines.