C语言实现strcmp

注意转化为unsigned char：

strcmp.h

 1 #ifndef STRCMP_H
 2 #define STRCMP_H
 3
 4 /***************************************************
 5 功能：比较字符串s1和s2。
 6 　一般形式：strcmp(s1，s2)
 7   返回值：
 8     当s1<s2时，返回值<0
 9     当s1=s2时，返回值=0
10     当s1>s2时，返回值>0
11 ****************************************************/
12
13 int cat_strcmp(const char *src, const char *dst) {
14     int ret = 0;
15
16     while (!(ret = (*(unsigned char *)src - *(unsigned char *)dst)) && *dst)
17         ++src, ++dst;
18
19     if (ret < 0)
20         ret = -1;
21     else if (ret > 0)
22         ret = 1;
23
24     return ret;
25 }
26
27 #endif

main:

 1 #include "strcmp.h"
 2
 3
 4 void test_strcmp();
 5
 6 int main() {
 7     test_strcmp();
 8
 9     return 0;
10 }
11
12 void test_strcmp() {
13     char *s1 = "compare", *s2 = "compase";
14     printf("%d\n", cat_strcmp(s1, s2));
15
16     char *s3 = "compare", *s4 = "compar";
17     printf("%d\n", cat_strcmp(s3, s4));
18
19     char *s5 = "compar", *s6 = "compare";
20     printf("%d\n", cat_strcmp(s5, s6));
21
22     printf("%d\n", cat_strcmp(s3, s6));
23 }

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