Q127194: FIX: CMap Template Class Leaks Non-Primitive KEY Objects

Article: Q127194
Product(s): Microsoft C Compiler
Version(s): winnt:2.0
Operating System(s): 
Keyword(s): kbcode kbnokeyword kbtemplate kbMFC kbVC200 kbVC200fix kbGrpDSMFCATL kbCollectionClass
Last Modified: 06-MAY-2001

-------------------------------------------------------------------------------
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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