strspn, strcspn - get length of a prefix substring

#include <string.h>
size_t strspn(const char *s, const char *accept);
size_t strcspn(const char *s, const char *reject);

The strspn() function calculates the length (in bytes) of the initial segment of s which consists entirely of bytes in accept.

The strcspn() function calculates the length of the initial segment of s which consists entirely of bytes not in reject.

The strspn() function returns the number of bytes in the initial segment of s which consist only of bytes from accept.

The strcspn() function returns the number of bytes in the initial segment of s which are not in the string reject.

memchr(3), strchr(3), string(3), strpbrk(3), strsep(3), strstr(3), strtok(3), wcscspn(3), wcsspn(3)