Q229904: PRB: CAxWindow Members Can Cause a Memory Leak

Article: Q229904
Product(s): Microsoft C Compiler
Version(s): 3.0,6.0
Operating System(s): 
Keyword(s): kbActiveX kbATL kbCOMt kbCtrl kbVC600 kbATL300 kbGrpDSMFCATL
Last Modified: 18-JUN-2002

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The information in this article applies to:

- The Microsoft Active Template Library (ATL) 3.0, included with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, version 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
   - Microsoft Visual C++.NET (2002) 
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SYMPTOMS
========

The CAxWindow CreateControl() and AttachControl() functions may leak memory if
not used correctly.

CAUSE
=====

The following two techniques of creating ActiveX controls on composite controls
(or any window supporting ATL containment) can result in memory leaks.

  //Intialize ATL control containment.
  AtlAxWinInit();

  //Create container window.
  HWND hWndCont = m_ax.Create(m_hWnd, rect, 0, WS_CHILD | WS_VISIBLE);

  //Create & activate ActiveX control
  HRESULT hr = m_ax.CreateControl("MSCAL.Calendar");

-OR-

  //Intialize ATL control containment.
  AtlAxWinInit();
  //Create container window
  HWND hWndCont = m_ax.Create(m_hWnd, rect, 0, WS_CHILD | WS_VISIBLE);

  // Create ActiveX control.
  CComPtr<IUnknown> spunk;
  HRESULT hr = CLSIDFromProgID(OLESTR("MSCAL.Calendar"), &clsid);
  hr = CoCreateInstance(clsid, NULL, CLSCTX_ALL, IID_IUnknown, (void**)&spunk);

  // Activate ActiveX control.
  HRESULT hr = m_ax.AttachControl(spunk);

In both techniques, the calls to Create() results in the creation of a
CAxHostWindow object. The call to CreateControl() or AttachControl() also
creates another CAxHostWindow Object. Upon destruction, the CAxHostWindow object
created by Create() is freed.

RESOLUTION
==========

Use one of the techniques mentioned in article Q218442 to create ActiveX
controls at run time.

STATUS
======

This behavior is by design.

REFERENCES
==========

For additional information, click the article number below to view the article
in the Microsoft Knowledge Base:

  Q192560 HOWTO: Adding ATL Control Containment Support to Any Window

  Q218442 HOWTO: Programmatically Add ActiveX Controls to Composite Control

Additional query words:

======================================================================
Keywords          : kbActiveX kbATL kbCOMt kbCtrl kbVC600 kbATL300 kbGrpDSMFCATL 
Technology        : kbVCsearch kbAudDeveloper kbATLsearch
Version           : :3.0,6.0
Issue type        : kbprb
Solution Type     : kbpending

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