Assignment problem

Someone explain why this doesn't work:

Code:

void tile::setCoords (coord* tr, coord* br, coord* bl, coord* tl)
{
        std::cout << "assigning [" << tr->x << ", " << tr->y << "]\n";
        std::cout << "assigning [" << br->x << ", " << br->y << "]\n";
        std::cout << "assigning [" << bl->x << ", " << bl->y << "]\n";
        std::cout << "assigning [" << tl->x << ", " << tl->y << "]\n";

        coords.topRight->x = tr->x;
        coords.topRight->y = tr->y;
        coords.bottomRight->x = br->x;
        coords.bottomLeft->y = br->y;
        coords.bottomLeft->x = bl->x;
        coords.bottomLeft->y = bl->y;
        coords.topLeft->x = tl->x;
        coords.topLeft->y = tl->y;

        std::cout << "assigned [" << coords.topRight->x << ", " << coords.topRight->y << "]\n";
        std::cout << "assigned [" << coords.bottomRight->x << ", " << coords.bottomRight->y << "]\n";
        std::cout << "assigned [" << coords.bottomLeft->x << ", " << coords.bottomLeft->y << "]\n";
        std::cout << "assigned [" << coords.topLeft->x << ", " << coords.topLeft->y << "]\n";
}

The answer will probably hit me in an hour - I've been doing that lately

Either they don't get assigned properly or I'm outputting what I don't mean to - I'm pretty sure it's the former since nothing gets drawn.

At a glance:

Code:

coords.bottomLeft->y = br->y;

bottomright y is not assigned, bottomleft y is assigned twice

Well I cleared that up, but this is still my output (along with nothing being drawn):

Code:

assigning [50, 0]
assigning [50, 50]
assigning [0, 50]
assigning [0, 0]
assigned [0, 0]
assigned [0, 0]
assigned [0, 0]
assigned [0, 0]

coords.topRight->x = tr->x;
coords.topRight->y = tr->y;
If they're the same type (I can't see why they shouldn't be), why not just do
*coords.topRight = *tr;

They are the same type but it still doesn't work. I could post my program in it's entirety so far, but tis rather long in several files.

Oh what the hell, this is bugging me like mad:

tile.h:

Code:

#pragma once

typedef struct _coord {
        int     x;
        int     y;
} coord;

class tile
{
        union _coords {
                coord*     topRight;
                coord*     bottomRight;
                coord*     bottomLeft;
                coord*     topLeft;
        } coords;

public:
        tile (void);
        ~tile (void);

        void    draw ();
        void    setCoords (coord* tr, coord* br, coord* bl, coord* tl);
        void    dumpCoords ();
};

tile.cpp

Code:

#include "StdAfx.h"
#include ".\tile.h"

tile::tile (void)
{
        coords.bottomLeft = new coord;
        coords.bottomRight = new coord;
        coords.topLeft = new coord;
        coords.topRight = new coord;
}

tile::~tile (void)
{
        delete coords.bottomLeft;
        delete coords.bottomRight;
        delete coords.topLeft;
        delete coords.topRight;
}


// draw
//      Draws tile @ coords
void tile::draw ()
{
        glBegin (GL_QUADS);
                glVertex2i (coords.topRight->x, coords.topRight->y);
                glVertex2i (coords.bottomRight->x, coords.bottomRight->y);
                glVertex2i (coords.bottomLeft->x, coords.bottomLeft->y);
                glVertex2i (coords.topLeft->x, coords.topLeft->y);
        glEnd ();
}

// setCoords
//
void tile::setCoords (coord* tr, coord* br, coord* bl, coord* tl)
{
        std::cout << "assigning [" << tr->x << ", " << tr->y << "]\n";
        std::cout << "assigning [" << br->x << ", " << br->y << "]\n";
        std::cout << "assigning [" << bl->x << ", " << bl->y << "]\n";
        std::cout << "assigning [" << tl->x << ", " << tl->y << "]\n";

        *coords.topRight = *tr;
        *coords.bottomRight = *br;
        *coords.bottomLeft = *bl;
        *coords.topLeft = *tl;

        std::cout << "assigned [" << coords.topRight->x << ", " << coords.topRight->y << "]\n";
        std::cout << "assigned [" << coords.bottomRight->x << ", " << coords.bottomRight->y << "]\n";
        std::cout << "assigned [" << coords.bottomLeft->x << ", " << coords.bottomLeft->y << "]\n";
        std::cout << "assigned [" << coords.topLeft->x << ", " << coords.topLeft->y << "]\n";
}

// dumpCoords
//      Output coords to stdout for debugging
void tile::dumpCoords ()
{
        std::cout << "tr: [" << coords.topRight->x << ", " << coords.topRight->y << "]\n";
        std::cout << "br: [" << coords.bottomRight->x << ", " << coords.bottomRight->y << "]\n";
        std::cout << "bl: [" << coords.bottomLeft->x << ", " << coords.bottomLeft->y << "]\n";
        std::cout << "tl: [" << coords.topLeft->x << ", " << coords.topLeft->y << "]\n";
}

EDIT: I take back what I said at the top because half of it isn't here - I don't think it's relevant but if you need it, just shout.

Why a union?

I naively decided I wanted the coords in the same place in memory. That is what a union does right? Right?

Well, unions were used to save memory on really weak machines. Now that they're so powerful, unions aren't needed anymore really (maybe in some cases, but I can't think of any).

I had a niggling the union might have something to do with it; I've removed it an now tis working!

But why?

Originally Posted by ahluka

I naively decided I wanted the coords in the same place in memory. That is what a union does right? Right?

Using union the coords are in exactly the same place in memory. That is, you actually have only one set of coordinates. They are all in the same memory location, and since a memory location can have only one value in it, all the coordinates are the same.

I think you'd like to use a struct or class instead...

Ah now I understand them. I've decided not to use a struct and just have them as private members - no reason not to.

For your viewing pleasure (and because I'm pleased with it):

http://www.ahluka.co.uk/tile_screen.JPG

The output is correct I'm just fiddling with it and have created two tiles in the same place. Don't ask.