INFO: Global Classes in Win32 (80382)


The information in this article applies to:

  • Microsoft Platform Software Development Kit (SDK) 1.0
This article was previously published under Q80382

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.
Modification Type:MinorLast Reviewed:7/11/2005
Keywords:kbinfo kbWndw kbWndwClass KB80382
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