Re: Serial thread continued

From:

"Doug Harrison [MVP]" <dsh@mvps.org>

Newsgroups:

microsoft.public.vc.mfc

Date:

Sun, 17 Aug 2008 10:44:48 -0500

Message-ID:

<c6hga4tb46ag17dq628u7oo15ab85prl7h@4ax.com>

On Sun, 17 Aug 2008 07:45:26 -0700 (PDT), Kahlua
<edward.frederick@verizon.net> wrote:

UINT SerialThread( LPVOID Param ) //Thread to monitor serial activity
{
HWND hDlg = (HWND)Param;
OVERLAPPED ovl = {0};
BYTE chread;
DWORD dwRead;
DWORD dwEventMask;
int i;

if(!SetCommMask(hCom, EV_RXCHAR))
   AfxMessageBox("Error setting ComMask");
BOOL running = TRUE;
while(running){
   if(WaitCommEvent(hCom, &dwEventMask, NULL)){
     if (!ReadFile (hCom, &chread, 1, &dwRead, &ovl)){
       DWORD err = ::GetLastError();
       TRACE(_T("Error reading data: %d\n"), err);
     }
     if (chread == 0x10){
       for (i=0; i<33; i++){
         if (!ReadFile (hCom, &chread, 1, &dwRead, &ovl)){
           DWORD err = ::GetLastError();
           TRACE(_T("Error reading data: %d\n"), err);
         }
         Bar[i] = chread;
       }
       ::PostMessage(hDlg, MY_SERIAL, (WPARAM)0, (LPARAM)0);
     }
   }
}
return TRUE;
}

Now NO errors are reported but all the data is not being received.
How did this solve anything but remove the old messages?

Your loop iterates exactly 33 times, and you set Bar[i] to the current
value of chread irrespective of whether or not ReadFile succeeded. Do you
see the problem with that?

Your loop needs to be structured something like this (modified to take best
advantage of whatever overlapped I/O features you're using):

offset = 0;
expecting = 33;
while (expecting != 0)
{
   if (read(expecting, buffer+offset, &dwRead))
   {
      offset += dwRead;
      expecting -= dwRead;
   }
   else
      deal with false return code
}

--
Doug Harrison
Visual C++ MVP