#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main ()
{
  int i;
  char str[] = "129th";
  char accept[] = "1234567890";
  i = strspn(str, accept);
  printf("str 前 %d 个字符都属于 accept\n",i);
  system("pause");
  return 0;
}

str 前 3 个字符都属于 accept

  int strcspn(char *str, char *accept);

#include<stdio.h>
#include <stdlib.h>
#include<string.h>
int main()
{
  char* s1 = "http://c.biancheng.net/cpp/u/biaozhunku/";
  char* s2 = "c is good";
  int n = strcspn(s1,s2);
  printf("The first char both in s1 and s2 is :%c\n",s1[n]); 
  printf("The position in s1 is: %d\n",n);
  system("pause");
  return 0;
}

The first char both in s1 and s2 is :c
The position in s1 is: 7

#include<stdio.h>
#include <stdlib.h>
#include<string.h>
int main()
{
  char* s1 = "http://c.biancheng.net/cpp/xitong/";
  char* s2 = "z -+*";
  if(strlen(s1) == strcspn(s1,s2)){
    printf("s1 is diffrent from s2!\n");
  }else{
    printf("There is at least one same character in s1 and s2!\n");
  }
  system("pause");
  return 0;
}

s1 is diffrent from s2!