C / C++ / MFC

(MessageHandler.C)
#include "MessageHandler.C"

thelonesquirrely wrote:

(in TaskQueue.h)
#ifndef TASK_QUEUE_H
#define TASK_QUEUE_H

#include "Tasks.h"

class MessageHandler; //forward declaration

// in A.h

class A{
  void what(){ printf("hello"); }
};

// in B.h where there is no #include of A.h

class A;  // forward declaration

class B{
A* myAPtr;     // declare typed pointer to the forward declared type
void myFunc();
};

// in B.cpp
#include "B.h"
#include "A.h"

// use the pointer because now we have the header that defines the type included
void B::myFunc(){ myAPtr->what(); }

1. In the Task constructor, you attempt to convert a const pointer to a non-const pointer - that's a no-no.
2. In TaskQueue.h, you effectively have two forward declarations of MessageHandler (one in TaskQueue.h, one from #including Tasks.h) - that's not allowed, so remove the one in TaskQueue.h - you always #include Tasks.h, so you know you'll have the forward declaration from there.
3. Again, in TaskQueue::setMessageHandler, you are converting a const pointer to a non-const pointer
4. You forward declared MessageHandler in TaskQueue.h - therefore, you do not know what methods MessageHandler has, so you can't call them in the header (as you've done in TaskQueue::doSomething). You can only call them after you've got a complete declaration of MessageHandler (i.e. in a TaskQueue.C, after you've #included MessageHandler.h)
5. You use '&this' in the MessageHandler constructor - this will give a MessageHandler**, as 'this' is a MessageHandler*
6. Your Task class isn't terminated with a semi-colon. This *can* cause torrents of incomprehensible error messages...