BUG: Error C2664 and C2582 While Using CArray Class

• Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0

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'

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 listed at the beginning of this article.

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
Version : winnt:5.0,6.0
Platform : winnt
Issue type : kbbug