Microsoft KB Archive/231995

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

Article ID: 231995

Article Last Modified on 12/11/2003

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APPLIES TO


 * Microsoft Visual C++ 5.0 Enterprise Edition
 * Microsoft Visual C++ 6.0 Enterprise Edition
 * Microsoft Visual C++ 5.0 Professional Edition
 * Microsoft Visual C++ 6.0 Professional Edition
 * Microsoft Visual C++ 6.0 Standard Edition

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This article was previously published under Q231995



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::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 that this is 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.
 * 1) include 

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 arrayA; };

B::B{} B::~B{}

class C {

public: C; ~C; void addElement;

protected: CArray arrayB; };

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

void main { }

Keywords: kbbug kbfix kbnoupdate kbcpponly KB231995

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