<系统函数实现>memcmp

这是我实现的memcmp函数：

 1 #include <stdio.h>

 2 #include <string.h>

 3 /*

 4 *int memcmp (const void *s1,const void *s2,size_t n);

 5 *º¯Êý˵Ã÷

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 8 *·µ»ØÖµ

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10 *p is src, q is des, len is length of p

11 *error     =-1

12 *p>q     >0

13 *p<q     <0

14 *p==q    =0

15 */

16 int _memcmp(const void *p,const void *q,int len)

17 {

18     if(!p || !q)

19     {

20         return -1;

21     }

22 

23    // while((*(char *)p != '\0') && (*(char *)q != '\0') && (len > 0))
　　　　while(len > 0)//this is strcmp , memcmp should't test \0

24     {

25         //printf("p %p:%d q %p:%d len %d\n",p,*(char *)p,q,*(char *)q,len);

26         if((*(char *)p - *(char *)q) != 0)        

27         {

28             

29             return (*(char *)p-*(char *)q);

30         }

31         p++;

32         q++;

33         len--;

34     }

35 

36     if((len > 0 ) && (*(char *)p != '\0'))

37     {

38         return 1;

39     }

40 

41     if((len > 0 ) && (*(char *)q != '\0'))

42     {

43         return -1;

44     }

45 

46     return 0;

47 }

48 

49 

50 int main(int argc, char **argv)

51 {

52     char *p = "abcfgf";

53 

54     char *q = "abcfg";

55 

56     int val;

57 

58     val = memcmp(p,q,6);

59     printf("sys val is %d\n",val);    

60 

61     val = _memcmp(p,q,6);

62 

63     printf("my val is %d  \n",val);

64 

65     return 0;

66 }