面试常备程序 — 字符串篇

1 strcmp

int strcmp(const char* s1, const char* s2)
{
    while(*s1 && (*s1==*s2))
        s1++,s2++;
    return *(const unsigned char*)s1-*(const unsigned char*)s2;
}

2 strlen

#include <stddef.h> /* for size_t */
size_t strlen(const char *s) {
    size_t i;
    for (i = 0; s[i] != '\0'; i++) ;
    return i;
}

或：

#include <stddef.h> /* for size_t */
size_t strlen(const char *s) {
    const char *p = s;
    while (*s) ++s;
    return s - p;
}

3 strcpy

char *strcpy(char *dest, const char* src)
#endif
{
    char *ret = dest;
    while (*dest++ = *src++)
        ;
    return ret;
}

4 strstr

#include <string.h> /* size_t memcmp() strlen() */
char *strstr(const char *s1, const char *s2)
{
    size_t n = strlen(s2);
    while(*s1)
        if(!memcmp(s1++,s2,n))
            return s1-1;
    return 0;
}

另参考这里：http://blog.youkuaiyun.com/lilong_dream/article/details/23655843

5 atoi

参考这里：http://blog.youkuaiyun.com/lilong_dream/article/details/19677643

        感谢阅读！

参考资料：

http://clc-wiki.net/wiki/C_standard_library:string.h