#include <stdlib.h>int mblen(const char *str, size_t size);
The mblen( ) function returns the length (in bytes) of a multibyte character pointed to by str. Only the first size number of characters are examined. It returns –1 on error.
If str is null, then mblen( ) returns nonzero if multibyte characters have state-dependent encodings. If they do not, zero is returned.
Related functions are mbtowc( ) and wctomb( ).