实现字符串函数，strlen(),strcpy(),strcmp(),strcat()

 1 #include<stdio.h>
 2 #include<stdlib.h>
 3
 4 int my_strlen(char *str);
 5 char *my_strcpy(char *dest, char *src);
 6 char *my_strcat(char *dest, char *src);
 7 int my_strcmp(char *str1,char *str2);
 8
 9 int main()
10 {
11     char dest[32] = "chen";
12     char src[32] = "chengha";
13     int res;
14     //printf("strlen(%s) = %d\n",str,my_strlen(str));
15     res = my_strcmp(dest,src);
16     printf("res = %d\n",res);
17     //puts(dest);
18     system("pause");
19     return 0;
20 }
21
22 int my_strlen(char *str)
23 {
24     int len = 0;
25     while(*str != ‘\0‘)
26     {
27         len++;
28         str++;
29     }
30     return len;
31 }
32
33 char *my_strcpy(char *dest, char *src)
34 {
35     char *address = dest;
36     while((*dest = *src) != ‘\0‘)
37     {
38         dest++;
39         src++;
40     }
41     return address;
42 }
43
44 char *my_strcat(char *dest, char *src)
45 {
46     char *address = dest;
47     while(*dest != ‘\0‘)
48         dest++;
49     while((*dest = *src) != ‘\0‘)
50     {
51         dest++;
52         src++;
53     }
54     return address;
55 }
56
57 int my_strcmp(char *str1,char *str2)
58 {
59     for(; *str1 == *str2; str1++, str2++)
60         if(*str1 == ‘\0‘)
61             return 0;
62     return *str1 - *str2;
63 }