DOCUMENT:Q127194  06-MAY-2001  [visualc]
TITLE   :FIX: CMap Template Class Leaks Non-Primitive KEY Objects
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:2.0
OPER/SYS:
KEYWORDS:kbcode kbnokeyword kbtemplate kbMFC kbVC200 kbVC200fix kbGrpDSMFCATL kbCollectionClass

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - The Microsoft Foundation Classes (MFC), used with:
    - Microsoft Visual C++, 32-bit Editions, version 2.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

When using the CMap template class, users may notice a memory leak when using
non-primitive objects as KEY values (for example, CString).

CAUSE
=====

The CMap class does not call the destructor for its KEYs when it does a
RemoveAll().

RESOLUTION
==========

Because the CMap class is implemented in AFXTEMPL.H, users can add a single line
to the CMap::RemoveAll() member function in this file to correct this problem.
The new line is marked with a //NOTE: in the following code:

   template<class KEY, class ARG_KEY, class VALUE, class ARG_VALUE>
   void CMap<KEY, ARG_KEY, VALUE, ARG_VALUE>::RemoveAll()
   {
       ASSERT_VALID(this);

       if (m_pHashTable != NULL)
       {
           // destroy elements (values and keys)
           for (UINT nHash = 0; nHash < m_nHashTableSize; nHash++)
           {
               CAssoc* pAssoc;
               for (pAssoc = m_pHashTable[nHash]; pAssoc != NULL;
                 pAssoc = pAssoc->pNext)
               {
                   DestructElements(&pAssoc->value, 1);

                   //NOTE: Additional call to destruct the keys!
                   DestructElements(&pAssoc->key, 1);
               }
           }
       }

       // free hash table
       delete[] m_pHashTable;
       m_pHashTable = NULL;

       m_nCount = 0;
       m_pFreeList = NULL;
       m_pBlocks->FreeDataChain();
       m_pBlocks = NULL;
   }

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article. This problem was corrected in the Microsoft
Foundation Classes version 3.1 included with Microsoft Visual C++, 32-bit
Edition, version 2.1.

Additional query words: CString CMap 3.00 KEY 2.00

======================================================================
Keywords          : kbcode kbnokeyword kbtemplate kbMFC kbVC200 kbVC200fix kbGrpDSMFCATL kbCollectionClass kbNoUpdate 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:2.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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