DOC: ConstructElements & DestructElements

SUMMARY

The documentation (included with the products listed above) for ConstructElements and DestructElements contains errors.

ConstructElements and DestructElements are two of the seven templated global helper functions used by MFC's templated collection classes such as CArray, CList, and CMap. ConstructElements is used to construct the elements stored in the collection classes and DestructElements is used to destruct the elements stored in the collection classes.

In Visual C++ 2.x, the MFC default implementation of ConstructElements does a bit-wise zero initialization to all the new elements, and the default implementation of DestructElements does nothing.

In Visual C++ 4.0 through 6.0, the MFC default implementation of ConstructElements not only does a bit-wise zero initialization to all the new elements but also calls the stored objects' constructors in a loop. This is different from the implementation in Visual C++ 2.x, but the documentation was not changed. See the "More Information" section in this article for the function implementation.

In addition, the MFC default implementation of DestructElements in Visual C++ 4.0 through 6.0, destructs the stored objects by calling their destructors. This is new in Visual C++ 4.x. See the "More Information" section in this article for the function implementation.

   template<class TYPE>
   inline void AFXAPI ConstructElements(TYPE* pElements, int nCount)
   {
     ASSERT(nCount == 0 ||
            AfxIsValidAddress(pElements, nCount * sizeof(TYPE)));

     // First do bit-wise zero initialization.
     memset((void*)pElements, 0, nCount * sizeof(TYPE));

     // Then call the constructor(s).
     for (; nCount--; pElements++)
         ::new((void*)pElements) TYPE;
   }

   template<class TYPE>
   inline void AFXAPI DestructElements(TYPE* pElements, int nCount)
   {
      ASSERT(nCount == 0 ||
             AfxIsValidAddress(pElements, nCount * sizeof(TYPE)));

      // Call the destructor(s).
      for (; nCount--; pElements++)
          pElements->~TYPE();
   }