Thread: 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;

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]

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?

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.