Microsoft KB Archive/89445

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INFO: Causes for Failure of DC-Creation Functions

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Q89445

3.00 3.10 WINDOWS kbprg

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The information in this article applies to:


 * Microsoft Windows Software Development Kit (SDK) 3.1

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SUMMARY
The DC-creation functions [CreateDC, CreateIC, and CreateCompatibleDC] can fail for several reasons. When one of these functions fails, it returns NULL. This article discusses eight causes for DC-creation failure and provides a resolution or explanation for each.

NOTE: Since the device driver would have already been loaded when CreateCompatibleDC is used, causes 1, 3, 5, 6, and 7 do not apply to it.

Causes for Failure

 * Application runs out of file handles.
 * Insufficient system resources.
 * Insufficient global memory.
 * Global atom tables are full.
 * Not enough selectors are free.
 * The DEVMODE structure passed in is not the right size.
 * The logical device (device driver) or the physical device is not found.
 * The function cannot initialize the created DC.

MORE INFORMATION
The order in which the causes are listed below does not provide any indication of how often each cause occurs.

Cause 1: Application Runs Out of File Handles
Resolution 1: Use the SetHandleCount function to open more file handles. For more information on the file limit, query in the Microsoft Knowledge Base on the following words:

"limits and open and files"

Explanation 1: The GDI requires a file handle to load the device driver and other files from disk.

Cause 2: Insufficient System Resources
Resolution 2: Verify that system resources are not lost because an application does not delete objects that it creates. If you are developing for Windows 3.1, use the debugging version of Windows 3.1. For other information on tracking down lost system resources, query in the Microsoft Knowledge Base on the following words:

"lost and heapwalk and system and resources"

The article &quot;Careful Windows Resource Allocation and Cleanup Improves Application Hygiene,&quot; in the September 1991 issue of the &quot;Microsoft Systems Journal&quot; discusses this issue further.

Explanation 2: These functions use the GDI's heap. Unless each application frees all the resources that it allocates, eventually Windows does not have enough memory to support the creation of DCs.

Cause 3: Insufficient Global Memory
Resolution 3: Close some applications and try again.

Explanation 3: The driver must be loaded into global memory.

Cause 4: Global Atom Tables Are Full
Resolution 4: Minimize the creation of global atoms. Try closing some applications.

Explanation 4: The GDI uses global atoms during the DC-creation process.

Cause 5: Not Enough Selectors Are Free
Resolution 5: Minimize the use of GlobalAlloc. Each GlobalAlloccall uses one of the limited selectors available to Windows (4096 in protected mode and 8192 in 386 enhanced mode). For more information, query in the Microsoft Knowledge Base on the following words:

"handle and limits and protected and enhanced mode"

Cause 6: The DEVMODE Structure Passed In Is Not the Right Size
Resolution 6: The size of the DEVMODE structure varies from printer to printer. You can find the size of the DEVMODE structure for a particular printer by calling ExtDeviceMode with wMode equal to zero.

Cause 7: The Logical Device (Device

Driver) or the Physical Device Is Not Found
Resolution 7: Check to see if you have the device driver and that the physical device is connected and ready for use. You can check this by attempting to print to that printer from other applications.

Cause 8: The Function Cannot Initialize the Created DC
Resolution 8: Restart Windows and try again.

Explanation 8: The objects used to initialize a DC are predefined. This problem is likely to occur only when one of the applications in the system has corrupted Windows' internal data.