Global Classes in Win32

 Last reviewed: November 2, 1995
Article ID: Q80382
The information in this article applies to:
  • Microsoft Win32 Application Programming Interface (API) included with: 

        - Microsoft Windows NT versions 3.5 and 3.51
    - Microsoft Windows 95 version 4.0

SUMMARY

Under 16-bit Windows, when an application wants to check whether or not a window class has been previously registered in the system, it typically checks hPrevInstance. Under 32-bit Windows and Windows NT, hPreviousInstance is always FALSE, because a class definition is not available outside the process context of the process that registers it. Thus, code that checks hPreviousInstance will always register the window class.

MORE INFORMATION

Under 32-bit Windows and Windows NT, a style of CS_GLOBALCLASS indicates that the class is available to every DLL in the process, not every application and DLL in the system, as it does in Windows 3.1.

To have a class registered for every process in the system under Windows NT:

  1. Register the class in a DLL.

  2. Use a style of CS_GLOBALCLASS.

  3. List the DLL in the following registry key.

    HKEY_LOCAL_MACHINE\S OFTWARE\ 

          Microsoft\
      Windows NT\
      CurrentVersion\
      Windows\
      AppInit_DLLs

This will force the DLL to be loaded into every process in the system, thereby registering the class in each and every process.

NOTE: This technique does not work under Windows 95.

For more information, please see "Window Classes in Win32," which is available on the MSDN CD, starting April 1994.

Additional reference words: 3.10 3.50 4.00 95
KBCategory: kbui
KBSubcategory: UsrCls

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Last reviewed: November 2, 1995
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