Unhandled Exception - Not Sure Why

[kutuup]

I am not sure why but this code (an attampt at a point and click game engine using Allegro 5) throws up an unhandled exception. The program starts and displays a picture, but as soon as the mouse is moved the exception pops up and the program crashes. I have highlighted the line (154) the IDE points to when it pops the exception message.

Any ideas on why would be greatly appreciated. I've been thinking about this all day and can't find the problem :(

// Adventure.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <allegro5/allegro.h>
#include <allegro5/allegro5.h>
#include <allegro5/allegro_image.h>
#include <allegro5/allegro_primitives.h>
#include <allegro5/allegro_font.h>
#include <allegro5/allegro_ttf.h>
#include <allegro5/allegro_audio.h>
#include <allegro5/allegro_acodec.h>
#include <iostream>
#include "string.h"
#include <windows.h>

using namespace std;

ALLEGRO_DISPLAY *display = NULL;
ALLEGRO_BITMAP *screenBitmapBuffer;
ALLEGRO_EVENT ev;
ALLEGRO_EVENT_QUEUE* event_queue = NULL;

class hotspot
{
private:
	string pairedScreen;
	string link;
public:
	int a,b,c,d;

	hotspot(string link, int a, int b, int c, int d)
	{
		this->link = link;
		this->a = a;
		this->b = b;
		this->c = c;
		this->d = d;
	}
};

class screen
{
private:

	ALLEGRO_BITMAP* imageStatic;
	hotspot* hotspots[8];

public:

	screen(const char* imageStatic)
	{
		this->imageStatic = al_load_bitmap(imageStatic);
	    this->hotspots[1] = new hotspot("test2",0,0,100,100);
		this->hotspots[2] = NULL;
		this->hotspots[3] = NULL;
		this->hotspots[4] = NULL;
		this->hotspots[5] = NULL;
		this->hotspots[6] = NULL;
		this->hotspots[7] = NULL;
		this->hotspots[8] = NULL;

	}
	screen()
	{
		this->imageStatic = NULL;
	}
	void display()
	{
		cout << this->imageStatic << endl;
		al_draw_bitmap(this->imageStatic,0,0,0);
		al_flip_display();
	}
	void setBitmap(const char* filename)
	{
		this->imageStatic = al_load_bitmap(filename);
	}
	hotspot* checkHotspot(int x)
	{
		return hotspots[x];
	}
		
};

void loadBitmapToScreen(screen* x, const char* filename)
{
	screenBitmapBuffer = al_load_bitmap(filename);
	if(screenBitmapBuffer)
	{
			x->setBitmap(filename);
			al_destroy_bitmap(screenBitmapBuffer);
	}
	else
	{
		cout << "Failed to load bitmap!" << endl;
	}

}

bool mouseWithin(hotspot* hot, int x, int y)
{
	cout << hot->a << endl;
	cout << hot->d << endl;

	//hotspot* hotCheck = hot;
	if(x > hot->a && x < hot->d && y > hot->a && y < hot->d)
	{
		
		return true;
	}
	else
	{

		return false;
	}
}

void initEngine()
{
    al_init();
    al_init_image_addon();
	al_init_font_addon();
	al_init_ttf_addon();
	al_install_audio();
	al_init_acodec_addon();
	al_install_mouse();
	display = al_create_display(500, 500);
	al_set_target_bitmap(al_get_backbuffer(display));
	if(!display)
	{
		cout << "Fatal Error: Unable to create display" << endl;
	}
}

int main(int argc, char** argv)
{
	initEngine();
	screen* Test = new screen();
	loadBitmapToScreen(Test, "Images\\01-ahead.png");
	Test->display();
	cout << "Hello World" << endl;
	al_set_new_display_flags(ALLEGRO_NOFRAME);

	event_queue = al_create_event_queue();
	al_register_event_source(event_queue, al_get_mouse_event_source());

	while(true)
	{
	al_wait_for_event(event_queue, &ev);

    if(ev.type == ALLEGRO_EVENT_MOUSE_AXES)
	{
		//system("cls");
	THIS LINE  -->	if(mouseWithin(Test->checkHotspot(1),ev.mouse.x,ev.mouse.y) == true)
		{
			cout << "mouse is within hotspot" << endl;
		}
		else
		{
			cout << "No hotspot" << endl;
		}
		//int gay = Test->checkHotspot(1)->a;
		cout << "X:" << ev.mouse.x << " Y:" << ev.mouse.y << endl;
		//
	}
	}
	system("PAUSE");
	return 0;
}

[rubberman]

My guess is that the Test->checkHotspot(1) argument to mousewithin() is returning a null pointer.

[mike_2000_17]

Lines 54 to 61 are off by one. You should know that indices in C/C++ go from 0 to N-1, that is, for an array hotspot* hotspots[8]; , the indices should go from 0 to 7, not from 1 to 8. This is really basic stuff.

Your default constructor does not initialize the "hotspots" array. And, as rubberman said, this means that the Test->checkHotspot(1) call returns a NULL pointer. When it is dereferenced in the mousewithin() function, you get a crash (segmentation fault or Access Violation, depending on your OS).

Your "screen" class holds dynamically allocated memory, yet you don't have a destructor (and nor do you have a deep-copy constructor and assignment operator). That's an error, you have memory leaking, and possibly more problems down the line. Read my tutorial on RAII for details.

You may have other errors, but start by solving the above-mentioned issues.

[tajendra]

I agree with Mike's view, below code is exception prone:-

this->hotspots[8] = NULL;

Array limits works from 0 to n-1, where n is the size of array. keep this thing in mind. And you must also free all memory which got alloctaed dynamically.

[kutuup]

Ah, dammit! It's always something so obvious! lol thanks guys. As for memory allocation and freeing memory, the code isn't finished yet, I'll be implementing that later :P