size_t mbstowcs(wchar_t *restrict pwcs, const char *restrict
The mbstowcs() function shall convert a sequence of characters that begins in the initial shift state from the array pointed to by s into a sequence of corresponding wide-character codes and shall store not more than n wide-character codes into the array pointed to by pwcs. No characters that follow a null byte (which is converted into a wide-character code with value 0) shall be examined or converted. Each character shall be converted as if by a call to mbtowc(), except that the shift state of mbtowc() is not affected.
No more than n elements shall be modified in the array pointed to by pwcs. If copying takes place between objects that overlap, the behavior is undefined.
The behavior of this function shall be affected by the LC_CTYPE category of the current locale. If pwcs is a null pointer, mbstowcs() shall return the length required to convert the entire array regardless of the value of n, but no values are stored.
If an invalid character is encountered, mbstowcs() shall return (size_t)-1 and may set errno to indicate the error.
Otherwise, mbstowcs() shall return the number of the array elements modified (or required if pwcs is null), not including a terminating 0 code, if any. The array shall not be zero-terminated if the value returned is n.
The mbstowcs() function may fail if:
The following sections are informative.
mblen() , mbtowc() , wctomb() , wcstombs() , the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>