The mbstowcs function converts a sequence of multi-byte characters that begin the initial shift state from the array pointed to by s into a sequence of corresponding codes and stores not more than n codes into the array pointed to by pwcs. No multi-byte characters that follow a null character (which is converted into a code with value zero) will be examined or converted. Each multi-byte character is converted as if by a call to the mbtowc function, except the shift state of the mbtowc function is not affected.
No more n elements will be modified in the array pointed to by pwcs. If copying takes place between objects that overlap, the behavior is undefined.