Question

I am writing an activex control that will access the parallel port and write the bytes to it. I am able to open the port succesfully but when i write it hangs at WriteFile function. Did i miss anything here? I am using Windows 7

HANDLE portHwd = CreateFile( _T("\\\\.\\LPT1" ), 
                        GENERIC_WRITE,
                        0,
                        NULL,
                        OPEN_EXISTING,
                        0,
                        NULL); 
      if (portHwd)
      {
          char outBuffer[] = _T("This is a test\r\n");
          int sz_buffer = strlen(outBuffer);

            DWORD bytes_written;
            if (!WriteFile( portHwd,
                  outBuffer,  
                  sz_buffer , 
                  &bytes_written, 
                  NULL))
            {
                  CloseHandle(portHwd);
                  GetLastError();
                  return 1;
            }

            CloseHandle(portHwd);
      }

Answer 1

If the port’s output buffer is full then WriteFile will hang until there is room to complete your request. Is there something attached to the port and reading from it?