src   dest
1  2  3  4  5   6
[ a ][ b ][ c ][ d ][ e ][ '\0' ][ ][ ][ ][ ][ ][ ][ ]

#include <iostream>
using namespace std;

void *memcopy( void *dest, const void *src, size_t count )
{
  if(dest==NULL||src==NULL)
    return NULL;
  char* Dest=(char*)dest;
  const char* Src=(char*)src;
  
  int i=0;
  
  while(i<count)
  {
    *Dest++=*Src++;
    i++;
  }
  
  return dest;
}

void *memmove(void *dest,const void *src,size_t count )
{
  if(dest==NULL||src==NULL)
    return NULL;

  char* Dest=(char*)dest;
  const char* Src=(char*)src;
  
  int i=0;
  if(src>dest)
  {
    while(i<count)//正向拷贝
    {
      *Dest++=*Src++;
      i++;
    }
  }
  else
  {
    Dest=Dest+count-1;//反向拷贝
    Src=Src+count-1;

    while(i<count)
    {
      *Dest--=*Src--;
      i--;
    }
  }

  
  
  return dest;
}



void main()
{
  char dest[80];
  memset(dest,'\0',80);
  char* src="memcpyteststring";
  int n;
  cout<<"How many char you want to copy from src to dest(memcpy): ";
  cin>>n;
  cout<<"The dest string is: "<<(char*)memcopy(dest,src,n)<<endl;
  cout<<"How many char you want to copy from src to dest(memcpy): ";
  cin>>n;
  cout<<"The dest string is: "<<(char*)memmove(dest,src,n)<<endl;
  return;
}