How To: Retrieve a Printer Device Context
This topic describes how to retrieve a printer device context. You can retrieve a printer device context by calling the CreateDC function directly, or it can be returned by a Print common dialog box.
When you display a Print common dialog box a user will be able to select the printer, the pages of the document, and the number of document copies they want to print. The Print common dialog box returns these selections in a data structure.
This topic describes how to obtain a printer device context by using the following methods.
Call CreateDC
If you know the device to which you want to print, you can call CreateDC and pass that information directly to the function. CreateDC returns a device context into which you can render the content to print.
The simplest call to retrieve a device context is shown in the code example that follows. The code in this example retrieves a device context to the default display device.
hDC = CreateDC(TEXT("DISPLAY"),NULL,NULL,NULL);
To render to a specific printer, you must specify "WINSPOOL" as the device and pass the correct name of the printer to CreateDC. You can also pass a DEVMODE structure in the call to CreateDC if you want to provide device-specific initialization data for the device driver when you create the device context.
The following example shows a call to CreateDC in which the "WINSPOOL" driver is selected and the printer name is specified by name.
printerDC = CreateDC( L"WINSPOOL", printerName, NULL, NULL);
You can obtain the exact printer name string to pass to CreateDC by calling the EnumPrinters function. The following code example shows how to call EnumPrinters and get the names of the local and locally connected printers. Because the size of the required buffer cannot be known in advance, the EnumPrinters is called two times. The first call returns the size of the required buffer. That information is used to allocate a buffer of the required size, and the second call to EnumPrinters returns the data that you want.
fnReturn = EnumPrinters(
PRINTER_ENUM_LOCAL | PRINTER_ENUM_CONNECTIONS,
NULL,
1L, // printer info level
(LPBYTE)NULL,
0L,
&dwNeeded,
&dwReturned);
if (dwNeeded > 0)
{
pInfo = (PRINTER_INFO_1 *)HeapAlloc(
GetProcessHeap(), 0L, dwNeeded);
}
if (NULL != pInfo)
{
dwReturned = 0;
fnReturn = EnumPrinters(
PRINTER_ENUM_LOCAL | PRINTER_ENUM_CONNECTIONS,
NULL,
1L, // printer info level
(LPBYTE)pInfo,
dwNeeded,
&dwNeeded,
&dwReturned);
}
if (fnReturn)
{
// Review the information from all the printers
// returned by EnumPrinters.
for (i=0; i < dwReturned; i++)
{
// pThisInfo[i]->pName contains the printer
// name to use in the CreateDC function call.
//
// When this desired printer is found in the list of
// returned printer, set the printerName value to
// use in the call to CreateDC.
// printerName = pThisInfo[i]->pName
}
}
Display a Print Common Dialog Box
You can choose from two Print common dialog boxes to display to a user; the newer dialog box, which you can display by calling the PrintDlgEx function, and the older style dialog box, which you can display by calling the PrintDlg function. The following sections describe how to call each dialog box from an application.
Using the PrintDlgEx Function
Call the PrintDlgEx function to display the Print property sheet. By using the property sheet, the user can specify information about the print job. For example, the user can select a range of pages to print, the number of copies, and so on. The PrintDlgEx can also retrieve a handle to a device context for the selected printer. You can use the handle to render output on the printer.
For sample code that illustrates the use of PrintDlgEx to retrieve a printer device context, see "Using the Print Property Sheet" in Using Common Dialog Boxes.
Using the PrintDlg Function
If your application must run on a system that does not support the PrintDlgEx function, such as on a system that is running a version of Windows earlier than Windows 2000, or does not need the extra functionality that the PrintDlgEx function provides, use the PrintDlg function. The following steps describe how to display the older style Print common dialog box.
- Initialize the PRINTDLG data structure.
- Call PrintDlg to display the Print common dialog box to the user.
- If the PrintDlg call returns TRUE, lock the returned DEVMODE structure memory. If the PrintDlg call returns FALSE, the user pressed the Cancel button in the Print common dialog box so there is nothing more to process.
- Allocate a local memory buffer that is large enough to contain a copy of the DEVMODE structure.
- Copy the returned DEVMODE structure to the locally allocated one.
- Save other information that is returned in the PRINTDLG structure and that you will need to process the print job.
- Free the PRINTDLG and the memory buffers it references.
The following example code illustrates how to use the PrintDlg function to get the device context and the name of selected printer.
// Display the printer dialog box so the user can select the
// printer and the number of copies to print.
BOOL printDlgReturn = FALSE;
HDC printerDC = NULL;
PRINTDLG printDlgInfo = {0};
LPWSTR localPrinterName = NULL;
PDEVMODE returnedDevmode = NULL;
PDEVMODE localDevmode = NULL;
int localNumberOfCopies = 0;
// Initialize the print dialog box's data structure.
printDlgInfo.lStructSize = sizeof( printDlgInfo );
printDlgInfo.Flags =
// Return a printer device context.
PD_RETURNDC
// Don't allow separate print to file.
// Remove these flags if you want to support this feature.
| PD_HIDEPRINTTOFILE
| PD_DISABLEPRINTTOFILE
// Don't allow selecting individual document pages to print.
// Remove this flag if you want to support this feature.
| PD_NOSELECTION;
// Display the printer dialog and retrieve the printer DC.
printDlgReturn = PrintDlg(&printDlgInfo);
// Check the return value.
if (TRUE == printDlgReturn)
{
// The user clicked OK so the printer dialog box data
// structure was returned with the user's selections.
// Copy the relevant data from the data structure and
// save them to a local data structure.
//
// Get the HDC of the selected printer
printerDC = printDlgInfo.hDC;
// In this example, the DEVMODE structure returned by
// the printer dialog box is copied to a local memory
// block and a pointer to the printer name that is
// stored in the copied DEVMODE structure is saved.
//
// Lock the handle to get a pointer to the DEVMODE structure.
returnedDevmode = (PDEVMODE)GlobalLock(printDlgInfo.hDevMode);
localDevmode = (LPDEVMODE)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY | HEAP_GENERATE_EXCEPTIONS,
returnedDevmode->dmSize);
if (NULL != localDevmode)
{
memcpy(
(LPVOID)localDevmode,
(LPVOID)returnedDevmode,
returnedDevmode->dmSize);
// Save the printer name from the DEVMODE structure.
// This is done here just to illustrate how to access
// the name field. The printer name can also be accessed
// by referring to the dmDeviceName in the local
// copy of the DEVMODE structure.
localPrinterName = localDevmode->dmDeviceName;
// Save the number of copies as entered by the user
localNumberOfCopies = printDlgInfo.nCopies;
}
else
{
// Unable to allocate a new structure so leave
// the pointer as NULL to indicate that it's empty.
}
// Free the DEVMODE structure returned by the print
// dialog box.
if (NULL != printDlgInfo.hDevMode)
{
GlobalFree(printDlgInfo.hDevMode);
}
}
else
{
// The user cancelled out of the print dialog box.
}
For more information about the PrintDlg function, see "Displaying the Print Dialog Box" in Using Common Dialog Boxes.
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