c++windowswinapiprintingwindows-shell

Trying to determine printer status always returns 0 for offline & online printers

My goal is to determine the current status of a printer. I found the following code. Here's a slightly modified version to fix memory leaks & bugs:

#include <Winspool.h>

int GetPrinterStatus( char* szPrnName )
{
  HANDLE          hHandle = 0;   // Handle of the printer

  DWORD           dwStatus = 0;  // Printer status we should receive

  DWORD           dwSize = 0;    // Size of memory we should
                                 // allocate for PRINTER_INFO_2

  PRINTER_INFO_2* pPrnInfo2 = 0; // Structure specifies detailed
                                 // printer information

  DEVMODE         DevMode = {0}; // Structure contains information
                                 // about the device initialization
                                 // and environment of a printer

  PRINTER_DEFAULTS PrnDef = { 0, &DevMode, PRINTER_ACCESS_USE };

  // Open printer with name szPrnName
  if( !OpenPrinter( szPrnName, &hHandle, &PrnDef ) )
    return -1; // Error

  // How many memory should be allocated for printer data?
  GetPrinter( hHandle, 2, 0, 0, &dwSize );
  if( !dwSize )
  {
    ClosePrinter( hHandle );
    return -1; // Error
  }

  // Allocate memory
  pPrnInfo2 = (PRINTER_INFO_2*)malloc( dwSize );

  // Receive printer details
  if(!GetPrinter( hHandle, 2, (LPBYTE)pPrnInfo2, dwSize, &dwSize ))
  {
    ClosePrinter( hHandle );
    free( pPrnInfo2 );
    return -1; // Error
  }

  dwStatus = pPrnInfo2->Status;

  // Free allocated memory
  free( pPrnInfo2 );

  // Close printer
  ClosePrinter( hHandle );

  return dwStatus;
}

So when I run it for this printer, that is offline:

enter image description here

Like this:

int status = GetPrinterStatus("POS58");

The status I receive is 0, which is exactly the same as when I call it for a functional printer

I then tried replacing OpenPrinter call with OpenPrinter2W and use PRINTER_OPTION_NO_CACHE option, but it didn't help.

What am I doing wrong?

Solution

  • This Offline state (yes, there is more than one) is not actually stored as a status bit but as the PRINTER_ATTRIBUTE_WORK_OFFLINE bit in pPrnInfo2->Attributes. See this KB article.

    It's set by the USB port monitor (USBMON) for a USB printer, but can also be toggled on or off by a user in the "See what's printing" window via the "Use Printer Offline" menu option:

    The "Use Printer Offline" menu option

    FYI, here is the status string this attribute shows in various places in Windows 10:

    The other offline state flags locations are:

    Note the exact status behaviour for each printer is driver-dependent because the driver can set whatever status it likes. For instance I don't recall seeing a network printer use PRINTER_ATTRIBUTE_WORK_OFFLINE, but I recently saw an Epson receipt printer use PRINTER_STATUS_NOT_AVAILABLE.