Q231995: FIX: Error C2664 and C2582 While Using CArray Class

Article: Q231995
Product(s): Microsoft C Compiler
Version(s): 5.0,6.0
Operating System(s): 
Keyword(s): kbCPPonly kbVC500bug kbVC600bug kbNoUpdate
Last Modified: 11-FEB-2002

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The information in this article applies to:

- Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SYMPTOMS
========

When a user-defined class contains a CArray and the same user-defined class is
nested in another class, you may get the following errors if no copy constructor
and assignment operator are provided for the class:

  main.cpp(52): error C2664: 'Add' : cannot convert parameter 1 from 'class B'
  to 'class B' No copy constructor available for class 'B'

After adding a copy constructor, you get the following error message:

  afxtempl.h(443): error C2582:'B' : 'operator =' function is unavailable
  afxtempl.h(1566):while compiling class-template member function 'void
  __thiscall CArray<class B,class B>::SetAtGrow(int,class B)'

CAUSE
=====

If the class that contains a CArray is nested in another class, then its objects
must be copied.

The compiler does not construct an implicit copy constructor and copy assignment
operator because the class in question has CArray as a member, which does not
have a copy constructor and copy assignment operator, and CArray inherits from
CObject, which has a protected copy construtor and a copy assignment operator.
The compiler tries to generate the implicit ones, but that generates a call to
CObject's version of them. Because they are protected, the above errors are
generated.

RESOLUTION
==========

You need to provide a copy constructor and an assignment operator for the class.

STATUS
======

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

This problem was corrected in Microsoft Visual C++ .NET.

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

The following example shows the correct use of the CArray class:

  // No compiler option needed.
  #include <afxtempl.h>

  struct A
  {
   int i;
   int j;
  };

  class B
  {

  	public:
  		B();
  		~B();

   // Need to define copy ctor and assignment operator.

  	B(const B& b){
  	// Your copy ctor body goes here.		
  	}
   
  	/* const B& */ void operator= (const B& b) { 
  	// Your assignment operator body goes here.
  	}

  	protected:
  		CArray<A, A> arrayA;
  };

  B::B(){}
  B::~B(){}

  class C
  {

  	public:
  		C();
  		~C();
  		void addElement();

  	protected:
  		CArray<B, B> arrayB;
  };

  C::C(){}
  C::~C(){}
  void C::addElement()
  {
  	B temp;
  	arrayB.Add(temp);
  }

  void main()
  {
  }

Additional query words:

======================================================================
Keywords          : kbCPPonly kbVC500bug kbVC600bug kbNoUpdate 
Technology        : kbVCsearch kbAudDeveloper kbVC500 kbVC600 kbVC32bitSearch kbVC500Search
Version           : :5.0,6.0
Issue type        : kbbug
Solution Type     : kbfix

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