C语言实现strcmp

注意转化为unsigned char：

strcmp.h

#ifndef STRCMP_H
#define STRCMP_H

/***************************************************
功能：比较字符串s1和s2。
　一般形式：strcmp(s1，s2)
  返回值：
    当s1<s2时，返回值<0
    当s1=s2时，返回值=0
    当s1>s2时，返回值>0
****************************************************/

int cat_strcmp(const char *src, const char *dst) {
    int ret = 0;

    while (!(ret = (*(unsigned char *)src - *(unsigned char *)dst)) && *dst) 
        ++src, ++dst;
    
    if (ret < 0)
        ret = -1;
    else if (ret > 0)
        ret = 1;
    
    return ret;
}

#endif

main:

#include "strcmp.h"


void test_strcmp();

int main() {
    test_strcmp();

    return 0;
}

void test_strcmp() {
    char *s1 = "compare", *s2 = "compase";
    printf("%d
", cat_strcmp(s1, s2));

    char *s3 = "compare", *s4 = "compar";
    printf("%d
", cat_strcmp(s3, s4));

    char *s5 = "compar", *s6 = "compare";
    printf("%d
", cat_strcmp(s5, s6));

    printf("%d
", cat_strcmp(s3, s6));
}

/**
拓展：
unsigned char和char：
http://blog.sina.com.cn/s/blog_5c6f793801019oij.html
http://blog.csdn.net/world7th/article/details/1543575
*/