INFO: Global Classes in Win32

ID: Q80382

The information in this article applies to:

Microsoft Win32 Software Development Kit (SDK)
Microsoft Windows 2000

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:

Use a style of CS_GLOBALCLASS.

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.

Additional query words:

Keywords : kbNTOS kbWinOS2000 kbSDKWin32 kbGrpUser kbWinOS95 kbWinOS98 kbWndw kbWndwClass
Version : WINDOWS:
Platform : WINDOWS
Issue type : kbinfo