strcpy/strcmp/memcpy/memcmp/strstr/ 的内部实现（转载）

来源：互联网发布：linux下zip版本编辑：程序博客网时间：2024/05/17 13:13

如下代码都是来自最新Linux kernel的库函数

//strcpy in linux kernel  linux-3.3/linux/lib/string.cchar *strcpy(char *dest, const char *src) {                 char *tmp = dest;            //很多时候可以在这儿对传入参数进行有效检查。内核里面没有这样做。         while ((*dest++ = *src++) != '\0')                 /* nothing */;         return tmp; }

//strcmp in linux kernelint strcmp(const char *cs, const char *ct) {         unsigned char c1, c2;          while (1) {                 c1 = *cs++;                 c2 = *ct++;                 if (c1 != c2)                         return c1 < c2 ? -1 : 1;                 if (!c1)                         break;         }         return 0; }

 void *memcpy(void *dest, const void *src, size_t count) {         char *tmp = dest;         const char *s = src;          while (count--)                 *tmp++ = *s++;         return dest; }

int memcmp(const void *cs, const void *ct, size_t count) {                   const unsigned char *su1, *su2;                int res = 0;                       for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)                 if ((res = *su1 - *su2) != 0)                         break;            return res; }

 char *strstr(const char *s1, const char *s2) {         size_t l1, l2;          l2 = strlen(s2);         if (!l2)                 return (char *)s1;         l1 = strlen(s1);         while (l1 >= l2) {                 l1--;                 if (!memcmp(s1, s2, l2))                         return (char *)s1;                 s1++;         }         return NULL; }

0 0