深入理解memmove()与memcpy()的区别以及实现方法

// MemMove.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include <iostream>
using namespace std;

void* memmove(void* dest, const void* src, size_t n)
{
 if (n <= 0)
 {
  cout << "Invalid count number." << endl;
 }
 if (dest == NULL || src == NULL)
 {
  cout << "The dest or src address is null." << endl;
 }
 if (dest == src)
 {
  cout << "The dest equals src." << endl;
 }
 if ((char*)dest <= (char*)src || (char*)dest >= (char*)src + n)
 {//对应图中2,3,4三种情况，赋值过程中，src中未使用的不会被覆盖
  char* de = (char*)dest;
  const char* sr = (const char*)src;
  while (n--)
  {
   *de++ = *sr++;
  }
 }
 else
 {//对应图中的第一种情况
  char* de = (char*)dest + n -1;
  const char* sr = (const char*)src + n - 1;
  while (n--)
  {
   *de-- = *sr--;
  }
 }
 return dest;
}

void* memmcpy(void* dest, const void* src, size_t n) 
{ 
  if (n <= 0) 
{ 
  cout << "Invalid count number." << endl; 
} 
 if (dest == NULL || src == NULL) 
 { 
     cout << "The dest or src address is null." << endl; 
 } 
 if (dest == src) 
 { 
   cout << "The dest equals src." << endl; 
 } 
 char* de = (char*)dest; 
 const char* sr = (const char*)src; 
 while (n--) 
 { 
   *de++ = *sr++; 
 } 
  return dest; 
} 

int _tmain(int argc, _TCHAR* argv[])
{
 char* p = "hello,world"; 
 char dest[12] = {0};
 char *q = (char*)memmove(dest,p,5);
 cout << dest << endl;   
 cout << q << endl; 
 return 0;  
}