Q118611: INFO: SetMessageQueue Used in MFC WinMain

Article: Q118611
Product(s): Microsoft C Compiler
Version(s): winnt:2.0,2.1
Operating System(s): 
Keyword(s): kbnokeyword kbMFC kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbWndwMsg kbGrpDSMFCATL kbArc
Last Modified: 07-MAY-2001

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The information in this article applies to:

- The Microsoft Foundation Classes (MFC), used with:
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.5, 1.51, 1.52 
   - Microsoft Visual C++, 32-bit Editions, versions 2.0, 2.1 
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SUMMARY
=======

Functions that use the applications message queue do not work correctly if they
are called in the constructor of a global or static object. SetMessageQueue is
called in the initialization code at the beginning of the MFC WinMain()
function. SetMessageQueue replaces the current message queue with a new message
queue. The constructors of global or static C++ objects are called before
WinMain(). If these constructors call functions that rely on the message queue,
the objects do not work properly.

MORE INFORMATION
================

MFC for Windows, version 2.5, calls SetMessageQueue in the AfxWinInit()
function, which is called by the MFC WinMain() function. The constructors for
global and static objects are called before WinMain(). These constructors should
not call functions that use the applications message queue or rely on the
message queue remaining the same after the constructor is executed. These
functions include:

- Creating a window

- Setting a timer (using SetTimer)

- Setting a hook (using SetWindowsHook)

- Posting a message

If any one of these things is done in the constructor and is not processed or
removed from the application's message queue before the constructor exits, it
will not work later in the application. To work around this, initialize each of
these objects in the CWinApp::InitInstance() function: Define an initialization
member function for the object and call it in the CWinApp::InitInstance()
function.

Additional query words: kbinf 1.50 2.00 2.10 2.50 2.51 2.52 3.00 3.10

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Keywords          : kbnokeyword kbMFC kbVC150 kbVC151 kbVC152 kbVC200 kbVC210 kbWndwMsg kbGrpDSMFCATL kbArchitecture 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:2.0,2.1
Issue type        : kbinfo

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