<系统函数实现>memcmp

这是我实现的memcmp函数：

 #include <stdio.h>
 #include <string.h>
 /*
 *int memcmp (const void *s1,const void *s2,size_t n);
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 *p is src, q is des, len is length of p
 *error     =-1
 *p>q     >0
 *p<q     <0
 *p==q    =0
 */
 int _memcmp(const void *p,const void *q,int len)
 {
     if(!p || !q)
     {
         return -;
     }

    // while((*(char *)p != '\0') && (*(char *)q != '\0') && (len > ))
　　　　while(len > 0)//this is strcmp , memcmp should't test \0
     {
         //printf("p %p:%d q %p:%d len %d\n",p,*(char *)p,q,*(char *)q,len);
         if((*(char *)p - *(char *)q) != )
         {

             return (*(char *)p-*(char *)q);
         }
         p++;
         q++;
         len--;
     }

     if((len >  ) && (*(char *)p != '\0'))
     {
         return ;
     }

     if((len >  ) && (*(char *)q != '\0'))
     {
         return -;
     }

     return ;
 }

 int main(int argc, char **argv)
 {
     char *p = "abcfgf";

     char *q = "abcfg";

     int val;

     val = memcmp(p,q,);
     printf("sys val is %d\n",val);    

     val = _memcmp(p,q,);

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

     return ;
 }