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 = ;

     while (!(ret = (*(unsigned char *)src - *(unsigned char *)dst)) && *dst)
         ++src, ++dst;

     if (ret < )
         ret = -;
     else if (ret > )
         ret = ;

     return ret;
 }

 #endif

main:

 #include "strcmp.h"

 void test_strcmp();

 int main() {
     test_strcmp();

     return ;
 }

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

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

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

     printf("%d\n", 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
*/