C和指针之memmove函数 memcpy函数 strcspn函数 strspn函数 strrstr函数实现

1  memmove函数的实现

  

   

    

     

    
    

     

      #include <stdio.h>
     
    
   

    

     

    
    

     

      #include <string.h>
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      void* my_memmove(void*dest, const void*src, size_t len) 
     
    
   

    

     

    
    

     

      {   
     
    
   

    

     

    
    

     
 char *pdest = (char *)dest;  
     
    
   

    

     

    
    

     
 const char* psrc = (char *)src;  
     
    
   

    

     

    
    

     
 if ((psrc < pdest) && (pdest < psrc + len))  
     
    
   

    

     

    
    

     

       { 
     
    
   

    

     

    
    

     

      		pdest = pdest + len - 1;
     
    
   

    

     

    
    

     

      		psrc = psrc + len - 1;
     
    
   

    

     

    
    

     
 while (len--)  
     
    
   

    

     

    
    

     

       {
     
    
   

    

     

    
    

     
			printf("*pstr is %c and *pdest is %c\n", *psrc, *pdest);
     
    
   

    

     

    
    

     

       *pdest-- = *psrc--;  
     
    
   

    

     

    
    

     

       }  
     
    
   

    

     

    
    

     

       }  
     
    
   

    

     

    
    

     
 else  
     
    
   

    

     

    
    

     

       {  
     
    
   

    

     

    
    

     
 while (len--)  
     
    
   

    

     

    
    

     

       {  
     
    
   

    

     

    
    

     

       *pdest++ = *psrc++;  
     
    
   

    

     

    
    

     

       }  
     
    
   

    

     

    
    

     

       }  
     
    
   

    

     

    
    

     
 return dest;  
     
    
   

    

     

    
    

     

      }  
     
    
   

    

     

    
    

     
 
     
    
   

    

     

    
    

     

      int main()
     
    
   

    

     

    
    

     

      {
     
    
   

    

     

    
    

     
	char s1[10] = "chenyu";
     
    
   

    

     

    
    

     
	printf("dest is %s\n", s1);
     
    
   

    

     

    
    

     
	printf("src is %s\n", s1 - 3);
     
    
   

    

     

    
    

     

      	memmove(s1, s1 - 3, 6);
     
    
   

    

     

    
    

     
	printf("s1 is %s\n", s1 + 3);
     
    
   

    

     

    
    

     
	char s2[10] = "chenyu";
     
    
   

    

     

    
    

     

      	my_memmove(s2, s2 - 3, 6);
     
    
   

    

     

    
    

     
	printf("s2 is %s\n", s2 + 3
     
    
  
 

文章来源: chenyu.blog.csdn.net，作者：chen.yu，版权归原作者所有，如需转载，请联系作者。

原文链接：chenyu.blog.csdn.net/article/details/84556251