strcspn() - span the complement of a string
#include <string.h>
size_t strcspn (const char *s, const char *charset)
The strcspn(3) function spans the initial part of the null-terminated string s as long as the characters from s do not occur in string charset (it spans the complement of charset).
The strcspn(3) function returns the number of characters spanned.
memchr(3)
strchr(3)
strpbrk(3)
strrchr(3)
strsep(3)
strspn(3)
strstr(3)
strtok(3)