Why disable CObject's copy constructor and assignment

Question

The MFC\'s root object CObject\'s copy constructor and assignment are disabled by default.

• In MSDN, there is a description

The st

Answer 1

Consider the following:

class CMyHandle : public CObject
{
    HANDLE hWin32;
public:
    CMyHandle()
    {
        hWin32 = SomeFunctionThatMakesHandle();
    }
    ~CMyHandle()
    {
        CloseHandle(hWin32);
    }
};

Now, if you copy CMyHandle, the handle ends up getting closed twice, and after the either one of the CMyHandle instances is destroyed, the other instance becomes invalid.

Since a large number of MFC's classes manage handles, this makes sense to force the creator of the class to explicitly override to create copy constructors and copy assignment operators.

EDIT: For example:

int main()
{
    CMyHandle h1; //CMyHandle's constructor initializes the handle
    {
        CMyHandle h2(h1); //Memberwise copy into h2. In this case, it copies the
                          //handle
    } //h2 destroyed, closes handle
    //h1 is now invalid (because the underlying handle was closed)!
}