PRB: C2027 When Using MFC Templated Collection Classes

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++, 32-bit Edition, version 4.0

SYMPTOMS

When you use MFC templated collection classes such as CArray, CList, and CMap to store elements of type HTREEITEM or HIMAGELIST, the compiler generates the following compiler error:

   afxtempl.h(73) : error C2027: use of undefined type '_TREEITEM'

   -or-

   afxtempl.h(73) : error C2027: use of undefined type '_TREEITEM'

CAUSE

HTREEITEM is type-defined (typedef) as struct _TREEITEM, and HIMAGELIST is type-defined (typedef) as struct _IMAGELIST in header file Commctrl.h located in the \Msdev\Include directory. Structures _TREEITEM and IMAGELIST are not defined in any header files or source files.

However, the template collection class helper function DestructElements in Visual C++ version 4.0 calls the destructor of the stored elements. In this case, the destructor of structure _TREEITEM or _IMAGELIST. Hence, the compiler error.

RESOLUTION

Define a dummy structure for _TREEITEM or _IMAGELIST in global scope. For example, the following code should compile cleanly:

// Other includes.

#include <afxtempl.h>

void TestFunction()

  // will now not generate the compiler error
  CArray< HTREEITEM, HTREEITEM >  MyArray1;
  CArray< HIMAGELIST, HIMAGELIST > MyArray2;

STATUS

This behavior is by design.