strcat strcpy strlen

 1 char * strcat(char * dest, const char * src) {

 2     assert(dest != NULL && src != NULL);

 3     char * p = dest;

 4     while (*p)

 5         p++;

 6     while (*p++ = *src++);

 7     return dest;

 8 }

 9 

10 int strlen(const char * src) {

11     int count = 0;

12     while (*src++)

13         count++;

14     return count;

15 }

16 

17 char * strcpy(char * dest, const char * src) {

18     assert(dest != NULL && src != NULL);

19     char * p = dest;

20     while (*p++ = *src++);

21     return dest;

22 }

其中要注意：

1 while（*p++）; // P最后指向‘\0’的下一位置

2 while (*p) p++; // p最后指向'\0'