#include <iostream>
#include <cstdio>
#include <cstring>

void * my_memmove( void * const dest, const char * const src, size_t n )
{
   // check parameters
   if( 0 == n )
   {
      return NULL;
   }
   if( NULL == dest || NULL == src )
   {
      return NULL;
   }

   char * psrc = (char *)src;
   char * pdest = (char *)dest;
   if( pdest <= psrc || pdest > psrc + n )
   {
      std::cout << "forward overlapping" << std::endl;
      // copy forward direction
      for( size_t i = 0; i < n; i++ )
      {
         *pdest = *psrc;
         pdest++;
         psrc++;
      }
   }
   else
   {
      std::cout << "backward overlapping" << std::endl;
      // copy backward direction
      pdest = pdest + n;
      psrc = psrc + n;
      for( size_t i = 0; i< n; i++ )
      {
         *pdest = *psrc;
         pdest--;
         psrc--;
      }
   }
   return dest;
}

int main( int argc, char ** argv )
{
   char *src = new char[100];
   sprintf( src, "%s", "hello world!" );
   char * dest = new char[100];
   memset( dest, 0, 100*sizeof(char ) );
   std::cout << src << std::endl;
   char * result = (char*)my_memmove( dest, src, strlen(src) );
   std::cout << result << std::endl;
   delete src;
   delete dest;
   return 0;
}