Assertion Debug Error(Using SDL)Can anyone detect error in the code?

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Code: 
#include "SDL.h"
#include "SDL_image.h"
#include <string>
#include <vector>
#include <cstdlib>

const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

const int FRAMES_PER_SECOND = 20;

const int DOT_WIDTH = 20;
const int DOT_HEIGHT = 20;

SDL_Surface* screen = NULL;
SDL_Surface* dot = NULL;
//direction of snake
const int DUP = 0;
const int DDOWN = 1;
const int DRIGHT = 2;
const int DLEFT = 3;
bool Game_Over = false;
std::vector<SDL_Rect>TurnLocation;
std::vector<int>TurnDirection;
SDL_Event event;
//the thing getting objects to grow its tail
class Snake
{
	private:
	SDL_Rect box;
	SDL_Rect last_turn;
	int num_follower;
	int direction;
	bool dChangeable;
	public:
	Snake();
	void move();
	void change_direction();
	void show();
	int get_direction();
	int get_follower();
	SDL_Rect get_location();
	bool Snake_Death(SDL_Rect fbox);
	void increase_follower();
};

class Timer
{
	private:
	int startTicks;
	int pauseTicks;

	bool started;
	bool paused;

	public:
	Timer();
	int get_ticks();
	void start();
	void stop();
	void pause();
	void unpause();
	bool is_started();
	bool is_paused();
};

class Follower
{
	private:
	SDL_Rect fbox;
	int direction;
	bool lastfollower;
	int followers;
	public:
	void make_last_follower();
	void set_last_follower(Follower *last_follower);
	void show();
	void follow();
	void set_direction();
	SDL_Rect follower_location();
	Follower(Snake *mySnake, std::vector<Follower> myFollower);
	~Follower();
};

class Food
{
	private:
	SDL_Rect food_location;

	public:
	Food();
	void change_location();
	void food_show();
	SDL_Rect food_get_location();
};
SDL_Surface* load_image(std::string filename)
{
	SDL_Surface* loadedImage = NULL;
	SDL_Surface* optimizedImage = NULL;

	loadedImage = IMG_Load(filename.c_str());
	if(loadedImage != NULL)
	{
		optimizedImage = SDL_DisplayFormat(loadedImage);
		SDL_FreeSurface(loadedImage);
		if(optimizedImage != NULL)
		{
			SDL_SetColorKey(optimizedImage, SDL_SRCCOLORKEY, SDL_MapRGB(optimizedImage->format, 0, 0xFF,0xFF));
		}
	}
	return optimizedImage;
}

bool init()
{
	if(SDL_Init(SDL_INIT_EVERYTHING) == -1)
	{
		return false;
	}

	srand(SDL_GetTicks());


	screen = SDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE);

	if( screen == NULL)
	{
		return false;
	}

	SDL_WM_SetCaption("GARRY ROCKSS!", NULL);

	return true;
}

bool load_files()
{
	dot = load_image("dot.bmp");

	if(dot == NULL)
	{
		return false;
	}

	return true;
}
void apply_surface(int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip = NULL)
{
	SDL_Rect offset;
	offset.x = x;
	offset.y = y;

	SDL_BlitSurface( dot, clip, screen, &offset);
}
void clean_up(std::vector<Follower> *theFollower)
{
	SDL_FreeSurface(dot);

	theFollower->clear();
	TurnLocation.clear();
	TurnDirection.clear();

	SDL_Quit();
}


bool check_collision(SDL_Rect A, SDL_Rect B)
{
	int ALeft, ARight;
	int AUp, ADown;
	int BLeft, BRight;
	int BUp, BDown;

	 ALeft = A.x;
	 ARight = A.x + A.w;
	 AUp = A.y;
	 ADown = A.y + A.h;
	 BLeft = B.x;
	 BRight = B.x +B.w;
	 BUp = B.y;
	 BDown = B.y + B.h;

	if ( ALeft> BRight)
	{
		return false;
	}

	if ( ARight< BLeft)
	{
		return false;
	}

	if( AUp > BDown)
	{
		return false;
	}
	if(ADown <BUp)
	{
		return false;
	}
	
	return true;
}
//THIS IS WHERE THE SNAKE CODE BEGINS
//THIS IS WHERE THE SNAKE CODE BEGINS
//THIS IS WHERE THE SNAKE CODE BEGINS
Snake::Snake()
{
	last_turn.x = 0;
	last_turn.y = 0;
	box.x = 0;
	box.y = 0;
	direction = DDOWN;
	num_follower = 0;
	dChangeable = false;
}
void Snake::increase_follower()
{
	num_follower++;
}

void Snake::move()
{

	if((box.x < 0) || (box.y < 0) || (box.x + DOT_WIDTH > SCREEN_WIDTH) ||(box.y + DOT_HEIGHT >SCREEN_HEIGHT))
	{
		Game_Over = true;
	}
	else 
	{
		switch(direction)
		{
		case DUP: box.y -= DOT_HEIGHT; break;
		case DDOWN: box.y += DOT_HEIGHT; break;
		case DRIGHT: box.x += DOT_WIDTH; break;
		case DLEFT: box.x -= DOT_WIDTH; break;
		}
	last_turn = get_location();
	TurnLocation.push_back(get_location());
	TurnDirection.push_back(get_direction());
	}
}

void Snake::change_direction()
{
	dChangeable = false;
	if(event.type == SDL_KEYDOWN)
	{
		SDL_Rect* p2last_turn = &last_turn;
		
		if(p2last_turn != NULL)
		{
		if(box.x>last_turn.x + DOT_WIDTH)
		{
			dChangeable = true;
		}
		if( box.y>last_turn.y + DOT_HEIGHT)
		{
			dChangeable = true;
		}
		if(box.x < last_turn.x - DOT_WIDTH)
		{
			dChangeable = true;
		}
		if(box.y < last_turn.y - DOT_HEIGHT)
		{
			dChangeable = true;
		}
		}
		else if(p2last_turn == NULL)
		{
			dChangeable = true;
		}
		if (dChangeable == true)
		{
			switch(event.key.keysym.sym)
			{
			case SDLK_UP: 
			if(direction == DDOWN)
			{
				break;
			}
			else
			{
				direction = DUP; break;
			}
			case SDLK_DOWN: 
				if(direction == DUP)
			{
				break;
			}
				else{
			direction = DDOWN; break;
			}
			case SDLK_RIGHT: 
				if(direction == DLEFT)
				{
				break;
				}
				else
				{
				direction = DRIGHT; break;
				}
			case SDLK_LEFT: 
					if(direction == DRIGHT)
					{
						break;
					}
				else
					{
					direction = DLEFT; break;
					}
			}
		}
	}
}

void Snake::show()
{
	apply_surface(box.x, box.y, dot, screen);
}

int Snake::get_direction()
{
	return direction;
}

int Snake::get_follower()
{
	return num_follower;
}
bool Snake::Snake_Death(SDL_Rect fbox)
{
	if((box.x <= 0) || (box.x >= SCREEN_WIDTH))
	{
		Game_Over = true;
		return true;
	}
	if((box.y <= 0) ||(box.y >= SCREEN_HEIGHT))
	{
		Game_Over = true;
		return true;
	}
		if(check_collision(box, fbox) == true)
		{
			Game_Over = true;
			return true;
		}
	return false;
	
}
SDL_Rect Snake::get_location()
{
	return box;
}


//THIS IS WHERE THE FOLLOWER CODE BEGINS
Follower::Follower(Snake *mySnake, std::vector<Follower> myFollower)
{
	if(mySnake->get_follower() == 0)
	{
		fbox = mySnake->get_location();
		switch(mySnake->get_direction())
		{
		case DUP:
		 fbox.y +=DOT_HEIGHT; break;
		case DDOWN:
			 fbox.y -=DOT_HEIGHT; break;
		case DRIGHT:
			 fbox.x -=DOT_HEIGHT; break;
		case DLEFT:
			 fbox.y +=DOT_HEIGHT; break;
		}
	}
	else
	{
		int i; 
		i =  myFollower.size();
		i--;
	
		direction = TurnDirection.back();

		switch(direction)
		{
			case DUP:
			fbox.x = myFollower[i].fbox.x; 
			fbox.y = myFollower[i].fbox.y + DOT_HEIGHT;
			break;
			case DDOWN:
			fbox.x = myFollower[i].fbox.x; 
			fbox.y = myFollower[i].fbox.y-DOT_HEIGHT;
			case DRIGHT:
			fbox.x = myFollower[i].fbox.x-DOT_WIDTH; 
			fbox.y = myFollower[i].fbox.y;
			case DLEFT:
			fbox.x = myFollower[i].fbox.x + DOT_WIDTH; 
			fbox.y = myFollower[i].fbox.y;
			
		}
	}
	lastfollower = true;
	mySnake->increase_follower();
}

Follower::~Follower()
{
	lastfollower = false;
	followers = 0 ;
	direction = -1;
	fbox.x = -1;
	fbox.y = -1;
}

void Follower::set_last_follower(Follower *last_follower)
{
	last_follower->lastfollower = false;
}

void Follower::show()
{
	apply_surface(fbox.x,fbox.y, dot, screen);
}
void Follower::follow()
{
	if(direction == DUP)
	{
		fbox.y -= DOT_HEIGHT;
	}
	if(direction == DDOWN)
	{
		fbox.y += DOT_HEIGHT;
	}
	if(direction == DRIGHT)
	{
		fbox.x +=DOT_WIDTH;
	}
	if(direction == DLEFT)
	{
		fbox.x -=DOT_WIDTH;
	}
}

void Follower::set_direction()
{
	if(TurnLocation.size() != 0)
	{
	for(int i = 0; i<TurnLocation.size(); i++)
	{
		if((fbox.x == TurnLocation[i].x) &&(fbox.y == TurnLocation[i].y))
		{
		direction = TurnDirection[i];
		if(lastfollower == true)
		{
			TurnLocation.erase(TurnLocation.begin() + i);
			TurnDirection.erase(TurnDirection.begin() + i);
		}
		}
		}
	}
}
void Follower::make_last_follower()
{
	lastfollower = true;
}

SDL_Rect Follower::follower_location()
{
	return fbox;
}

Timer::Timer()
{
	startTicks = 0;
	pauseTicks = 0;
	bool started = false;
	bool paused = false;
}

void Timer::start()
{
	started = true;
	startTicks = SDL_GetTicks();
}

void Timer::stop()
{
	started = false;
	paused = false;
}

void Timer::pause()
{
	paused = true;

	pauseTicks = SDL_GetTicks() - startTicks;
}


void Timer::unpause()
{
	if(paused == true)
	{
		paused = false;
		startTicks = SDL_GetTicks() - pauseTicks;
	}
}


int Timer::get_ticks()
{
	if((started == true) && (paused == true))
	{
		return pauseTicks;
	}
	else if(started == true)
	{
		return SDL_GetTicks() - startTicks;
	}
}

Food::Food()
{
	food_location.x = rand() % SCREEN_WIDTH;
	food_location.y = rand() % SCREEN_HEIGHT;
}

void Food::change_location()
{
	food_location.x = rand() % SCREEN_WIDTH;
	food_location.y = rand() % SCREEN_HEIGHT;
}
void Food::food_show()
{
	apply_surface(food_location.x, food_location.y, dot, screen);
}
SDL_Rect Food::food_get_location()
{
	return food_location;
}


int main(int argc, char* args[])
{
	bool quit = false;

	if(init() == false)
	{
		return 1;
	}

	if(load_files() == false)
	{
		return 1;
	}

	Timer fps;
	Snake theSnake;
	Food theFood;
	std::vector<Follower> theFollower;
	
	while((quit == false) &&(Game_Over == false))
	{
		fps.start();
		while(SDL_PollEvent(&event))
		{
			theSnake.change_direction();
			if(event.type == SDL_QUIT)
			{
				quit = true;
				Game_Over = true;
			}
		}

		if(check_collision(theSnake.get_location(), theFood.food_get_location()) == true)
		{	
			Follower newFollower(&theSnake,theFollower);
			theFollower.push_back(newFollower);
			for(int i = 0; i<theFollower.size(); i++)
			{
				theFollower[i].set_last_follower(&theFollower[i]);
			}
			int b = theFollower.size() - 1;
			theFollower[b].make_last_follower();
			theFood.change_location();
		}
		theSnake.move();
		SDL_FillRect(screen, &screen->clip_rect, SDL_MapRGB(screen->format, 0xFF,0xFF,0xFF));
		theSnake.show();
		theFood.food_show();
		if(theFollower.size() != 0)
		{
			for(int i = 0; i<theFollower.size(); i++)
			{
				if(theSnake.Snake_Death(theFollower[i].follower_location()) == true)
				{
				quit = true;
				}
				theFollower[i].follow();
				theFollower[i].show();

			}
		}

		if(fps.get_ticks() < 1000/FRAMES_PER_SECOND)
		{
			SDL_Delay((1000/FRAMES_PER_SECOND) - fps.get_ticks());
		}

	}
	clean_up(&theFollower);
	return 0;
}
 
s3rius

s3rius

Linux is only free if your time is worthless.
Reaction score
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Holy batman, that's a lot of code to debug.

My eagle eyes have spotted a potential problem:

newFollower.makeFollower(theSnake.get_location(), theSnake.get_direction(), theFollower.back().follower_location());

That part - in my eyes you've never added any elements to theFollower when this line runs first. theFollower.back() will give a debug assertion error if the vector is empty.

Do you know how to use break points? (I don't know how much programming you've done..)

If you left-click on the bar to the left of your script, you can set a break point (the red dot):
Unbenannt.png

When you run your program it will execute until it hits a break point, then it'll stop and show you the code.
You can hover over variables and look at their current state:
Unbenannt.png

(By pressing F5 you can continue program execution).
This way you can put break points in front of places where you think the vector could bug out, and look at it's content.
So if theFollower is empty when you call .back() then you got your culprit.

If that's not the case, examine the debug assertion that fails. The important bit is the expression:

Unbenannt.png

If it's "vector iterator + offset out of range" then you should look at parts like vector.back().
If it's "vector subscript out of range" then it's probably where you loop through all elements of theFollower and show them. (you loop too far, the vector[x] (with x being a number outside the vector's range) causes this error, for example)
 
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