字符串操作函数 strstr 实现

最新推荐文章于 2025-01-16 14:25:53 发布

最新推荐文章于 2025-01-16 14:25:53 发布 · 89 阅读

本文详细介绍了C语言中用于查找子字符串的strchr和strstr函数的内部实现过程，包括如何通过字符比较和循环遍历来定位子字符串在主字符串中的首次出现位置。

 /*
  The  strstr()  function finds the first occurrence of the substring needle 
  in the string haystack.  The terminating  '\0' characters are not compared.
 */
char *strstr_r(char *s1, char *s2)
{
   /*  s1 : hellwoleddlfjwo, s2: wol */
   const char *p1, *p2;
   if((*s2) == '\0') /* Early versions of Linux libc,strstr  would not allow an empty needle argument */
       return s1;


   while( (s1 = strchr(s1, *s2)) != NULL) {
       p1 = s1;     /* found first character of s2, see if the rest matches */
       p2 = s2;
       while((*p1++ == *p2++)) {
          if(*p1 == '\0')
              return s1; /* both strings ended together */
       }
       if(*p2 == '\0') {
          break;
       }
       s1++;
   }


    return s1;
}