FIX: CMap Template Class Leaks Non-Primitive KEY Objects

The information in this article applies to:

• The Microsoft Foundation Classes, included with: Microsoft Visual C++, 32-bit Edition, 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.