memcpy
原型：extern void *memcpy(void *dest, void *src, unsigned int count);
包含：#include <string.h>;
功能：由src所指内存区域复制count个字节到dest所指内存区域。
说明：src和dest所指内存区域不能重叠，函数返回指向dest的指针。
memset
包含：extern void *memset(void *buffer, int c, int count);
用法：#include <string.h>;
功能：把buffer所指内存区域的前count个字节设置成字符c。
说明：返回指向buffer的指针

#include <stdio.h>
#include <string.h>
int main(void)
{
   char src[] = "******************************";
   char dest[] = "abcdefghijlkmnopqrstuvwxyz0123456709";
   char *ptr;
   printf("destination before memcpy: %s\n", dest);
   ptr =(char*) memcpy(dest, src, strlen(src));
   if (ptr)
      printf("destination after memcpy:  %s\n", dest);
   else
      printf("memcpy failed\n");
   return 0;
}

else
      printf("memcpy failed\n");

想当然的吧？？？

把src全部复制的话就跟strcat()一样了。
其他的话，谢谢分享了！

#include <stdio.h>
#include <string.h>
int main(void)
{
   char src[] = "******************************";
   char dest[] = "abcdefghijlkmnopqrstuvwxyz0123456709";
   char *ptr = NULL;//这样比较好，但在这边没差啦
   printf("destination before memcpy: %s\n", dest);
   ptr =(char*) memcpy(dest, src, strlen(src));
   if (ptr) //这样很。。。。好像不管怎么样都不会返回0；memcpy在MSDN里的返回值是这样的 Return Valuememcpy returns the value of dest.

      printf("destination after memcpy:  %s\n", dest);
   else
      printf("memcpy failed\n");
   return 0;
}

MSDN对这个函数的解释是这样的
memcpy
Copies characters between buffers.

Routine Required Header
memcpy <memory.h> or <string.h>


void *memcpy( void *dest, const void *src, size_t count );
Parameters
dest
New buffer
src
Buffer to copy from
count
Number of characters to copy
Libraries
All versions of the C run-time libraries.

Return Values
memcpy returns the value of dest.

Remarks
The memcpy function copies count bytes of src to dest. If the source and destination overlap, this function does not ensure that the original source bytes in the overlapping region are copied before being overwritten. Use memmove to handle overlapping regions.

Example
/* MEMCPY.C: Illustrate overlapping copy: memmove
 * handles it correctly; memcpy does not.
 */

#include <memory.h>
#include <string.h>
#include <stdio.h>

char string1[60] = "The quick brown dog jumps over the lazy fox";
char string2[60] = "The quick brown fox jumps over the lazy dog";
/*                           1         2         3         4         5
 *                  12345678901234567890123456789012345678901234567890
 */

void main( void )
{
   printf( "Function:\tmemcpy without overlap\n" );
   printf( "Source:\t\t%s\n", string1 + 40 );
   printf( "Destination:\t%s\n", string1 + 16 );
   memcpy( string1 + 16, string1 + 40, 3 );
   printf( "Result:\t\t%s\n", string1 );
   printf( "Length:\t\t%d characters\n\n", strlen( string1 ) );

   /* Restore string1 to original contents */
   memcpy( string1 + 16, string2 + 40, 3 );

   printf( "Function:\tmemmove with overlap\n" );
   printf( "Source:\t\t%s\n", string2 + 4 );
   printf( "Destination:\t%s\n", string2 + 10 );
   memmove( string2 + 10, string2 + 4, 40 );
   printf( "Result:\t\t%s\n", string2 );
   printf( "Length:\t\t%d characters\n\n", strlen( string2 ) );

   printf( "Function:\tmemcpy with overlap\n" );
   printf( "Source:\t\t%s\n", string1 + 4 );
   printf( "Destination:\t%s\n", string1 + 10 );
   memcpy( string1 + 10, string1 + 4, 40 );
   printf( "Result:\t\t%s\n", string1 );
   printf( "Length:\t\t%d characters\n\n", strlen( string1 ) );
}

Output
Function:   memcpy without overlap
Source:      fox
Destination:   dog jumps over the lazy fox
Result:      The quick brown fox jumps over the lazy fox
Length:      43 characters

Function:   memmove with overlap
Source:      quick brown fox jumps over the lazy dog
Destination:   brown fox jumps over the lazy dog
Result:      The quick quick brown fox jumps over the lazy dog
Length:      49 characters

Function:   memcpy with overlap
Source:      quick brown dog jumps over the lazy fox
Destination:   brown dog jumps over the lazy fox
Result:      The quick quick brown dog jumps over the lazy fox
Length:      49 characters

感谢楼主