CList on mfc problems

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Hi!
I have a problem using CList on mfc.
I'm trying to build a paint on mfc.

I have a Class for Shape, and derived class Rectangle and Circle.
on Shape i stored the color of the shape and on Rectangle I stored the 2 points to draw the rectangle.
I made a CList<cshape,cshape> list.
When I debug I see that only the color stored in the list(CShape) and not the points of the shape(CRectangle).
Why it happens?
Thanks!

C++

#pragma once
class CShape
{
public:
	CShape();
	CShape(int, int, int);
	virtual ~CShape();
	void setGreen(int);
	void setRed(int);
	void setBlue(int);
	int getRed();
	int getGreen();
	int getBlue();

protected:
	int red;
	int green;
	int blue;
};

#pragma once
#include "Shape.h"
class CRectangle :
	public CShape
{
public:
	CRectangle();
	CRectangle(CPoint , CPoint ,int , int, int);
	~CRectangle();
	CPoint getPoint1();
	CPoint getPoint2();
private:
	CPoint p1;
	CPoint p2;
};

//Some function...
.
.
.
  CRectangle r(CPoint(0, 0), CPoint(1, 1), 255, 255, 255);
  CList <CShape, CShape> l;
  l.AddHead(r);
.
.
.

Posted 9-Jan-15 21:39pm

w_ommer

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2 solutions

Solution 1

You need to show the implementation of your constructors (and other functions). As it stands your classes do nothing.

Posted 9-Jan-15 23:10pm

Richard MacCutchan

Comments

w_ommer 10-Jan-15 23:47pm

There is no implemntation in the constructors yes.
only this->x = x etc...

Richard MacCutchan 11-Jan-15 3:35am

So where is the actual implementation that shows the creation of a CRectangle with the missing data members?

Shmuel Zang 11-Jan-15 3:48am

It seems like the problem isn't in the classes' constructors but, in the list's declaration. (See my solution)

Richard MacCutchan 11-Jan-15 4:03am

That's possible, but we still need to see the actual code to be sure.

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Shmuel Zang · Accepted Answer · 2015-01-10T21:19:00

Solution 3

That's because you store the items of your CList by value (your declaration is: CList <CShape, CShape> l;). In that way, when you add elements to your list the copy-constructor of CShape is called and copies only the data-members of CShape.

You may want to use pointers instead . Something like:

C++

CRectangle* r = new CRectangle(CPoint(0, 0), CPoint(1, 1), 255, 255, 255);
CList <CShape*> l;
l.AddHead(r);

// You should delete the CRectangle when you remove it from the list.

Or, a shared_ptr. Something like:

C++

std::shared_ptr<CRectangle> r(new CRectangle(CPoint(0, 0), CPoint(1, 1), 255, 255, 255));
CList <std::shared_ptr<CShape> > l;
l.AddHead(r);

// When you remove the CRectangle form the list, it is deleted by the shared_ptr destructor.

Posted 10-Jan-15 21:19pm

Shmuel Zang

Updated 17-Jan-15 20:59pm

v3

Comments

w_ommer 17-Jan-15 4:36am

hi,
Well it workes, but only when i do:
l.addHead(&object);

but when the object is deleted also the data in the list is gone...
what is the problem?

Shmuel Zang 17-Jan-15 13:54pm

Do you wonder way the data of a deleted object is gone? Maybe because it is deleted...
You send &object as a parameter. - Does it a pointer to the stack (not a good idea...)?
If you want to store an object and delete it (and keep the data in the list), you should store a copy of the object (and, delete it when you remove it from the list).

w_ommer 17-Jan-15 14:35pm

thaks...how do i do that?

just to remind, i didnt call any destructor or delete()...

Shmuel Zang 18-Jan-15 2:59am

You should create the CRectangle on the heap (instead of on the stack). See the updated solution.

w_ommer 18-Jan-15 12:04pm

GREAT it works!!
The first sugestion was good