Causes for Failure of DC-Creation Functions

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.1 and 3.0

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

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

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 GlobalAlloc() call 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.