C / C++ / MFC

int _tmain(int argc, _TCHAR* argv[])
{
 HANDLE g_hIOCP = ::CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 0);
 if (g_hIOCP == NULL)
 {
  cout<<"can not create io completion port"<<endl;
  return 1;
 }
 // open file with FILE_FLAG_OVERLAPPED flag to ensure that io is asynchronous
 HANDLE hFile = CreateFile(L"d:\\test.abc", GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, NULL);
 if (hFile == NULL)
 {
  cout<<"can not open file"<<endl;
 }
 HANDLE hTest = ::CreateIoCompletionPort(hFile, g_hIOCP, (ULONG_PTR)hFile, 0);
 if (hTest != g_hIOCP)
 {
  cout<<"failed to associate file to completion port"<<GetLastError()<<endl;
  return 0;
 }
 for(int i = 0; i < 5; ++i)
 {
  OVERLAPPED ov = {0};
  char szBuf[128];
  DWORD lpNumberOfBytesRead = 0;
  BOOL b = ::ReadFile(hFile, szBuf, 128, &lpNumberOfBytesRead, &ov);
  // when run on Windows Vista, ReadFile always returns FALSE, and GetLastError returns ERROR_IO_PENDING
  if (b == FALSE)
  {
   cout<<"ReadFile failed，last error code is："<<::GetLastError()<<endl;
   if (::GetLastError() == ERROR_IO_PENDING)
   {
    cout<<"read file asynchronously"<<endl;
   }
  }
  // when run on Windows XP, ReadFile always returns TRUE
  else
  {
   cout<<"read file synchronously"<<lpNumberOfBytesRead<<"bytes"<<endl;
  }
 }
 return 0;
}