FIX: C2440 Expanding Template with a Pointer to a Nested Class (149327)

The information in this article applies to:

Microsoft Visual C++, 32-bit Editions 4.0
Microsoft Visual C++, 32-bit Editions 4.1
Microsoft Visual C++, 32-bit Enterprise Edition 4.2
Microsoft Visual C++, 32-bit Professional Edition 4.2
Microsoft Visual C++, 32-bit Enterprise Edition 5.0
Microsoft Visual C++, 32-bit Professional Edition 5.0

This article was previously published under Q149327

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 that this is a bug in the Microsoft products that are 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;

}

Modification Type:	Minor	Last Reviewed:	7/5/2005
Keywords:	kbBug kbfix kbVC600fix KB149327