这两个副本函数都用于将 n 个字符从源对象复制到目标对象，但它们有一些区别，如下所述。

• 如果源指针和目标指针指向的内存区域重叠，则 memcpy 复制函数会显示未定义的行为。 memmove 函数在重叠的情况下具有定义的行为。 因此，每当有疑问时，使用 memmove 代替 memcpy 会更安全。

  #include <string.h>
  #include <stdio.h>
  char str1[50] = "I am going from Delhi to Gorakhpur";
  char str2[50] = "I am going from Gorakhpur to Delhi";
  int main( void )
  {
    //Use of memmove
    printf( "Function:\tmemmove with overlap\n" );
    printf( "Orignal :\t%s\n",str1);
    printf( "Source:\t\t%s\n", str1 + 5 );
    printf( "Destination:\t%s\n", str1 + 11 );
    memmove( str1 + 11, str1 + 5, 29 );
    printf( "Result:\t\t%s\n", str1 );
    printf( "Length:\t\t%d characters\n", strlen( str1 ) );
    //Use of memcpy
    printf( "Function:\tmemcpy with overlap\n" );
    printf( "Orignal :\t%s\n",str2);
    printf( "Source:\t\t%s\n", str2 + 5 );
    printf( "Destination:\t%s\n", str2 + 11 );
    memcpy( str2 + 11, str2 + 5, 29 );
    printf( "Result:\t\t%s\n", str2 );
    printf( "Length:\t\t%d characters\n", strlen( str2 ) );
    return 0;
  }
  

  运行结果：

  Function: memmove with overlap
  Orignal : I am going from Delhi to Gorakhpur
  Source: going from Delhi to Gorakhpur
  Destination: from Delhi to Gorakhpur
  Result: I am going going from Delhi to Gorakhpur
  Length: 40 characters
  Function: memcpy with overlap
  Orignal : I am going from Gorakhpur to Delhi
  Source: going from Gorakhpur to Delhi
  Destination: from Gorakhpur to Delhi
  Result: I am going going fring frakg frako frako
  Length: 40 characters
  

• 与 memcpy 相比，memmove 函数较慢，因为在 memmove 中，额外的临时数组用于从源复制 n 个字符，然后将存储的字符复制到目标内存。

• memcpy 在转发副本时很有用，但 memmove 在重叠场景的情况下很有用。