C# Signatures:

[DllImport("winspool.drv", CharSet=CharSet.Auto, SetLastError=true)]
static extern int OpenPrinter(string pPrinterName, out IntPtr phPrinter, PRINTER_DEFAULTS pDefault);

[DllImport("winspool.drv",SetLastError=true)]
static extern int OpenPrinter(string pPrinterName, out IntPtr phPrinter, int pDefault);

Both signatures will work fine, it is a matter of whether you need a higher level of access to the printer or not. For 'read' only access such as monitoring printer queues, you don't need to pass in a PRINTER_DEFAULTS instance for the last parameter, you can just pass zero (0) if you declare the extern function pDefault parameter as an int. You will need a PRINTER_DEFAULTS structure if you need to change any properties of the printer such as setting the duplex value of the printer.

VB Signatures:

    <DllImport("winspool.drv", EntryPoint:="OpenPrinterA", _
    SetLastError:=True, CharSet:=CharSet.Ansi, _
    ExactSpelling:=True, _
    CallingConvention:=CallingConvention.StdCall)> _
    Private Shared Function OpenPrinter(ByVal pPrinterName As String, _
                    ByRef phPrinter As Int32, _
                    ByVal pDefault As Int32) As Boolean

    <DllImport("winspool.drv", EntryPoint:="OpenPrinterA", ExactSpelling:=True, _
    SetLastError:=True, CallingConvention:=CallingConvention.StdCall, _
    CharSet:=CharSet.Ansi)> _
    Private Shared Function OpenPrinter(ByVal pPrinterName As String, _
    ByRef hPrinter As IntPtr, ByVal pDefault As PRINTER_DEFAULTS) As Boolean
    End Function

User-Defined Types:

PRINTER_DEFAULTS

Notes:

As always, only do SetLastError=true if you actually intend to call GetLastError.

ClosePrinter

Tips & Tricks:

Sample Code:

How to cancel a print job:

IntPtr pHandle;
PRINTER_DEFAULTS defaults = new PRINTER_DEFAULTS();
byte b = 0;
OpenPrinter(printerName, out pHandle, defaults);
SetJobA(pHandle, (int)jobID, 0, ref b, (int)Job_Control.Cancel);
ClosePrinter(pHandle);

Alternative Managed API:

The System.Management API allows for lots of printer stuff, but doesn't let you delete a print job in Win2K.

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