C++ possible constructor error violation writing location - c++

Question

I have added these functions to my code, and my program started crashing randomly showing
Unhandled exception at 0x6C7B52E7 (SDL2.dll) in SDL_2.exe: 0xC0000005: Access violation writing location 0xFF00000C. Debugger shows at completely random pieces of code, that worked perfectly before, which leads me to think, that these new functions mess up the memory.
void ObstacleSet::move()
{
Obstacles.push_back(Obstacle(mScreenWidth, mScreenHeight / 6 + 100, 10, 10, Coin, -29, 0));
Obstacles.push_back(Obstacle(mScreenWidth, mScreenHeight / 6 + 120, 10, 10, Coin, -29, 0));
Obstacles.push_back(Obstacle(mScreenWidth, mScreenHeight / 6 + 140, 10, 10, Coin, -29, 0));
Obstacles.push_back(Obstacle(mScreenWidth, mScreenHeight / 6 + 160, 10, 10, Coin, -29, 0));
Obstacles.push_back(Obstacle(mScreenWidth, mScreenHeight / 6 + 180, 10, 10, Coin, -29, 0));
for (auto &i : Obstacles)
{
i.move();
}
}
void ObstacleSet::outCheck(unsigned int &score)
{
for (unsigned int i = 0; i < getSize();)
{
if (getVelX(i) < 0 && (getX(i) + getW(i) <= 0))
{
eraseObstacle(i);
score++;
}
else if (getVelX(i) > 0 && (getX(i) >= mScreenWidth))
{
eraseObstacle(i);
score++;
}
else if (getVelY(i) > 0 && (getY(i) + getH(i) >= mScreenHeight))
{
eraseObstacle(i);
score++;
}
else if (getVelY(i) < 0 && (getY(i) <= 0))
{
eraseObstacle(i);
score++;
}
else
{
++i;
}
}
}
Apparently, i have some memory leak, or a dangling pointer somehow appears, but i just can not see where. Maybe i have a wrong constructor or something.
ObstacleSet is a class, that holds all Obstacles in a list.
#ifndef MOBSTSET_H
#define MOBSTSET_H
#include <SDL.h>
#include <cstdlib>
#include "my_OBSTACLES.h"
#include <list>
class ObstacleSet
{
public:
ObstacleSet(int ScreenWidth, int ScreenHeight);
int mScreenWidth;
int mScreenHeight;
void clear();
//Function, that moves the set depending on current time
void move();
//Render set on screen
void render(SDL_Renderer *Renderer);
unsigned int getSize();
float getX(int);
float getY(int);
int getW(int);
int getH(int);
float getVelX(int);
float getVelY(int);
Type GetType(int);
void eraseObstacle(int);
void outCheck(unsigned int &score);
std::list<Obstacle>::iterator getEnd();
private:
//Vector to hold all obstacles
std::list <Obstacle> Obstacles;
};
#endif
These appear in my main game loop one after another
Obstacle class header
#ifndef MYOBSTACLE_H
#define MYOBSTACLE_H
#include <SDL.h>
#include <cmath>
#include <vector>
#include <cstdlib>
enum Type
{
Wall,
Coin
};
class Obstacle
{
public:
Obstacle();
//Initializer with parameters
Obstacle(float x, float y, int w, int h, Type type, float VelocityX = 0, float VelocityY = 0);
float VelocityX = 0;
float VelocityY = 0;
float xPos;
float yPos;
int mWidth;
int mHeight;
//Type of obstacle
Type OBSType;
//Render obstacle on screen
void render(SDL_Renderer *Renderer);
//Move obstacle
void move();
int mRed = 200;
int mGreen = 200;
int mBlue = 20;
bool color_up = false;
};
#endif
These are my constructors for Obstacle
Obstacle::Obstacle() : xPos(10), yPos(10), mWidth(10), mHeight(10), VelocityX(0), VelocityY(0), OBSType(Coin), mRed(200), mGreen(200), mBlue(20), color_up(false)
{
printf("Obstacle created!");
}
Obstacle::Obstacle(float x, float y, int w, int h, Type type, float velocityX, float velocityY) : xPos(x), yPos(y), mWidth(w), mHeight(h), VelocityX(velocityX), VelocityY(velocityY), OBSType(type), mRed(200), mGreen(200), mBlue(20), color_up(false)
{
}
Here are some functions of ObstacleSet
void ObstacleSet::eraseObstacle(int number)
{
unsigned N = number;
std::list<Obstacle>::iterator i = Obstacles.begin();
if (Obstacles.size() > N)
{
std::advance(i, N);
}
Obstacles.erase(i);
}
unsigned int ObstacleSet::getSize()
{
return Obstacles.size();
}
float ObstacleSet::getX(int number)
{
unsigned N = number;
std::list<Obstacle>::iterator i = Obstacles.begin();
if (Obstacles.size() > N)
{
std::advance(i, N);
}
return i->xPos;
}
std::list<Obstacle>::iterator ObstacleSet::getEnd()
{
return Obstacles.end();
}
SDL Initialization code
bool init()
{
//Initialization flag
bool success = true;
//Initialize SDL
if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_JOYSTICK | SDL_INIT_AUDIO) < 0)
{
printf("SDL could not initialize! SDL Error: %s\n", SDL_GetError());
success = false;
}
else
//Set texture filtering to linear
if (!SDL_SetHint(SDL_HINT_RENDER_SCALE_QUALITY, "1"))
{
printf("Warning: Linear texture filtering not enabled!");
}
//Initialize SDL_mixer
if (Mix_OpenAudio(44100, MIX_DEFAULT_FORMAT, 2, 2048) < 0)
{
printf("SDL_mixer could not initialize! SDL_mixer Error: %s\n", Mix_GetError());
success = false;
}
//Check for joysticks
if (SDL_NumJoysticks() < 1)
{
printf("Warning: No joysticks connected!\n");
}
else
{
//Load joystick
gGameController = SDL_JoystickOpen(0);
if (gGameController == NULL)
{
printf("Warning: Unable to open game controller! SDL Error: %s\n", SDL_GetError());
}
}
//Create window
gWindow = SDL_CreateWindow("Jello demo", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
if (gWindow == NULL)
{
printf("Window could not be created! SDL Error: %s\n", SDL_GetError());
success = false;
}
else
{
//Create vsynced renderer for window
gRenderer = SDL_CreateRenderer(gWindow, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);
if (gRenderer == NULL)
{
printf("Renderer could not be created! SDL Error: %s\n", SDL_GetError());
success = false;
}
else
//Initialize renderer color
SDL_SetRenderDrawColor(gRenderer, 0xFF, 0xFF, 0xFF, 0xFF);
//Initialize PNG loading
int imgFlags = IMG_INIT_PNG;
if (!(IMG_Init(imgFlags) & imgFlags))
{
printf("SDL_image could not initialize! SDL_image Error: %s\n", IMG_GetError());
success = false;
}
//Initialize SDL_ttf
if (TTF_Init() == -1)
{
printf("SSDL_ttf could not initialize! SDL_ttf Error: %s\n", TTF_GetError());
success = false;
}
}
return success;
}
Maybe I have got a memory leak or a dangling pointer, but I can't find where the mistake is. I will be VERY glad if anyone could find where i am wrong. Write me if you need any additional code pieces

Answer 1

Unless you have an invariant somewhere that guarantees that ObstacleSet never calls anything on an empty Obstacles list there is a potential problem.
This code has undefined behaviour on an empty list
float ObstacleSet::getX(int number)
{
unsigned N = number;
std::list<Obstacle>::iterator i = Obstacles.begin();
if (Obstacles.size() > N)
{
std::advance(i, N);
}
return i->xPos;
}
Trying to fix it
float ObstacleSet::getX(int number)
{
unsigned N = number;
std::list<Obstacle>::iterator i = Obstacles.begin();
if (Obstacles.size() > N)
{
std::advance(i, N);
}
if (i != Obstacles.end())
return i->xPos;
// handle empty
return ERRORPOS; // or throw or assert or ...
}
Same with all other functions that access the list.

Answer 2

Some issues I see in the code:
In ObstacleSet::move() you add five obstacles to the list. It looks like the list can grow indefinitely, resulting in memory overflow.
You don't check if Obstacles are empty in eraseObstacle(), getX() and perhaps in other functions which you haven't shown.

Answer 3

So apparently, there error was not in the code i provided. I initialized SDL_mixer wrongly. I loaded audio like this
if (Mix_OpenAudio(44100, MIX_DEFAULT_FORMAT, 2, 2048) < 0), but sampling rate of wav file i provided was not MIX_DEFAULT_FORMAT, which is 22050.
Anyway, thanks to everybody, who tried to help me with my code. It was a pleasant experience to use stackoverflow for the fisrt time.