Question

We have some print server software written in C# (which P/Invokes functions from winspool.drv). Some of the “printers” are actually virtual printers that print to a directory. The code to install such a printer is:

public override void AddLocalDirectoryPrinter(string printerName, string directory)
{
    IntPtr hPrinter = IntPtr.Zero;

    try
    {
        PRINTER_DEFAULTS pd;
        PRINTER_INFO_2 pi2;

        pd.datatype = null;
        pd.pDevMode = IntPtr.Zero;
        // Access = PRINTER_ALL_ACCESS
        // http://msdn.microsoft.com/en-us/library/cc244650%28v=prot.10%29.aspx
        pd.desiredAccess = PRINTER_ALL_ACCESS;

        // Attributes = PUBLISHED | DO_COMPLETE_FIRST | SHARED
        // http://msdn.microsoft.com/en-us/library/aa394363%28v=vs.85%29.aspx
        pi2.attributes = 0x2208;
        pi2.averagePpm = 0;
        pi2.jobs = 0;
        pi2.defaultPriority = 0;
        pi2.comment = "Auto-Generated by [name of program]";
        pi2.datatype = "RAW";
        pi2.pDevMode = IntPtr.Zero;
        pi2.driverName = "Generic / Text Only";
        pi2.location = string.Empty;
        pi2.parameters = string.Empty;
        pi2.portName = directory;
        pi2.printerName = printerName.ToUpperInvariant();
        pi2.printProcessor = "WinPrint";
        pi2.priority = 0;
        pi2.pSecurityDescriptor = IntPtr.Zero;
        pi2.sepFile = string.Empty;
        pi2.serverName = string.Empty;
        pi2.shareName = printerName.ToUpperInvariant();
        pi2.startTime = 0;
        pi2.status = 0;
        pi2.untilTime = 0;

        hPrinter = AddPrinter(null, 2, ref pi2);

        if (hPrinter == IntPtr.Zero)
        {
            throw new Win32Exception(Marshal.GetLastWin32Error());
        }
    }
    catch (Exception ex)
    {
        throw new PrintingException("Failed to add printer", ex);
    }
    finally
    {
        if (hPrinter != IntPtr.Zero)
        {
            ClosePrinter(hPrinter);
        }
    }
}

On 32-bit Windows XP, the above code runs without error. But on 64-bit Windows 7, the call to AddPrinter fails with Windows error 1796 (“The specified port is unknown”).

Why does it work on one version of Windows but not another?

Answer 1

It turns out that I just needed to build a 64-bit version of dirport.dll.