strcspn(3) BSD Library Functions Manual strcspn(3)
strcspn -- span the complement of a string
Standard C Library (libc, -lc)
#include <string.h> size_t strcspn(const char *s1, const char *s2);
The strcspn() function spans the initial part of the null-terminated string s1, as long as the characters from s1 do not occur in string s2 (it spans the complement of s2). In other words, it computes the string array index in s1 of the first character of s1 which is also in s2, else the index of the first null character.
The strcspn() function returns the number of characters spanned.
The strcspn() function conforms to ISO/IEC 9899:1990 (``ISO C90''). BSD June 4, 1993 BSD
Mac OS X 10.8 - Generated Fri Aug 31 05:43:40 CDT 2012