1 #include <string.h> 2 3 #define N 256 4 5 size_t 6 strspn(const char *s, const char *b) 7 { 8 char map[N], *os; 9 10 memset(map, 0, N); 11 while(*b) 12 map[*(unsigned char *)b++] = 1; 13 os = s; 14 while(map[*(unsigned char *)s++]) 15 ; 16 return s - os - 1; 17 } 18