wcsspn - get length of a prefix wide-character substring

#include <wchar.h>
size_t wcsspn(const wchar_t *wcs, const wchar_t *accept);

The wcsspn() function is the wide-character equivalent of the strspn(3) function. It determines the length of the longest initial segment of wcs which consists entirely of wide-characters listed in accept. In other words, it searches for the first occurrence in the wide-character string wcs of a wide-character not contained in the wide-character string accept.

The wcsspn() function returns the number of wide characters in the longest initial segment of wcs which consists entirely of wide-characters listed in accept. In other words, it returns the position of the first occurrence in the wide-character string wcs of a wide-character not contained in the wide-character string accept, or wcslen(wcs) if there is none.

strspn(3), wcscspn(3)