strcspn(3) - Linux man page
Name
strspn, strcspn - search a string for a set of bytesSynopsis
#include <string.h> size_t strspn(const char *s, const char *accept); size_t strcspn(const char *s, const char *reject);
Description
The strcspn() function calculates the length of the initial segment of s which consists entirely of bytes not in reject.
Return Value
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.