DOCUMENT:Q149327  30-JUL-2001  [visualc]
TITLE   :FIX: C2440 Expanding Template with a Pointer to a Nested Class
PRODUCT :Microsoft C Compiler
PROD/VER:
OPER/SYS:
KEYWORDS:kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600fix

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

 - The C/C++ Compiler (CL.EXE), used with:
    - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
    - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
    - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
    - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
    - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

At the point where a class template is expanded using a pointer to a nested
class, the compiler reports the following errors (generated by the sample code
listed in this article):

   [FileName](14) : error C2440: 'initializing' : cannot convert from 'class
   A::B' to 'class A::B *' (new behavior; please see help)

   [FileName](14) : error C2439: 't' : member could not be initialized

Lines 13 and 14 in the sample code are:

   template <class T> C<T>::C() : t(T())  // error
      {

RESOLUTION
==========

There are three possible workarounds to this problem. Each is stated here in
terms of the sample code included in this article:

 - Remove t(T()) from the initializer list and add t = T(); to the body of the
   constructor. This workaround assumes there is an operator= defined for class
   T.

 - Change C<A::B *> c; to C<A::B&> c; or C<A::B> c:

 - Change the definitions of class A and class B to that B is no longer nested
   in the definition of A.

STATUS
======

Microsoft has confirmed this to be a bug in the Microsoft products listed at the
beginning of this article.

MORE INFORMATION
================

In this case, the problem is caused by the attempt to initialize the data member
t.

Sample Code
-----------

   /* Compile options needed: None */ 
   template <class T> class C
   {
   public:
     C();
   private:
     T t;
   };

   template <class T> C<T>::C() : t(T())  // error
   {
   }

   class A
   {
   public:

      class B
      {
      };

   };

   main()
   {

      C<A::B *> c;
      return 0;

   }

Additional query words:

======================================================================
Keywords          : kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600fix 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Issue type        : kbbug
Solution Type     : kbfix

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

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