why getting DebugBreak() on deleting an object

Question

I have an MFC dialog, which is called Dlg1

myobject* Dlg1 = new myobject();

This dialog has a parent dialog called A; I have a function in A, which is called on closing:

A::Destroy()
{
     if(Dlg1 )
           delete  Dlg1; // this is triggering `DebugBreak(); here i get A.exe has triggered a breakpoint, 
     // the rest of the code 
}

If I close Dlg1 dialog, manually by clicking on the close button, then close the main dialog A, then everything is fine no problem. However, if Dlg1 is running and I close A, then I get DebugBreak(). This issue occurs only in debug mode, in the release mode no problem.

Answer 1

If we are to assume that the code you posted in your question is the actual code you're using, the issue may be this:

myobject* Dlg1 = new myobject();

Note that Dlg1 is a local variable, not a member variable. Then you have this:

A::Destroy()
{
  if (Dlg1 )
     delete  Dlg1; 
}

The Dlg1 in the code above is the member variable Dlg1 of class or struct A. It more than likely was never initialized, due to your code creating a dynamic object locally by mistake. Issuing a delete on an uninitialized pointer will wreak havoc.

If this is the issue, then to fix it, one suggestion is to have somewhere:

A::SomeFuntion()
{
    //...
    Dlg1 = new myobject();  // set the member variable Dlg1, not a local variable.
    //...,
}

where SomeFunction would be another member function of A.