Program crashes when trying to delete Canon ( canon ball )

[MongKong]

I press space and i shoot but when canon ball reaches "water" it should delete itself but instead it crashes which normally means i'm trying to access memory which no longer exists.... but i don't know what to do...

and these are the error i get:

QGraphicsItem::x

function inside Canon Class moveCanonBall()

and this

This is Canon's header file:

and this is Canon's source file:

#include "canon.h"
#include "game.h"
#include "math.h"
#include "soundeffects.h"
#include <QGraphicsPixmapItem>
#include <QPixmap>
#include <QObject>
#include <QTimer>
#include <QDebug>
#include <QMediaPlayer>

#include "soundeffects.h"

extern Game *game;

bool Canon::CanonBallGone=false;

Canon::Canon(QGraphicsItem *parent): QGraphicsPixmapItem(parent){

    ballHitEnd = false;

    setPixmap(QPixmap(":/Images/Canon_1.png")); // 30x25
    SoundEffects::canonBallShot(1);
    game->scene->addItem(this);

    // bullet cords
    moveByY = 1.0;
    moveDown = false;
    splashLasting = 0;

    // shrani direction katero player trenutno is facing // saves the direction which the player is currently facing
    // (left==3, right ==1)
    direction = game->player->getLeftOrRightDirection();
    if(direction == 1){
        xPl = game->player->x()+83;
        yPl = game->player->y()+42;
        newX = game->player->x()+83;
    }else if(direction == 3){
        xPl = game->player->x()-18;
        yPl = game->player->y()+42;
        newX = game->player->x()-18;
    }

    time = new QTimer();
    connect(time,SIGNAL(timeout()),this,SLOT(moveCanonBall()));
    time->start(5);
}

Canon::~Canon(){
    delete time;
}

bool Canon::getCanonBallGone(){
    return CanonBallGone;
}

bool Canon::setCanonBallGoneToFalse(){
    CanonBallGone = false;
}

bool Canon::setCanonBallGoneToTrue(){
    CanonBallGone = true;
}


void Canon::moveCanonBall(){

    if(direction==1 && ballHitEnd==false){
        // s pomocjo balisticne enacbe zracunamo y  // with a help of this function we calculate y  ( parabolic movement of the canon ball )
        help = (0.5*(x()-xPl)*tan(0.6)-(0.5 *pow((x()-xPl),2))
                / (2*pow(20,2)*pow(cos(0.6),2))+yPl)-yPl;
        moveByY = yPl - help;
        setY(moveByY);
        setPos(x(),y());

        // povecujemo x za 1.5  // incrementing x by 1.5
        setX(x()+1.5);

        // ce je canon ball v vodi spremenimo sliko v splash sliko  // if canon ball hits its final destination we change picture to a splash 
        if(y() >= yPl+32){

            ballHitEnd = true;
            setPixmap(QPixmap(":/Images/Splash_1.png"));
        }

    }


    else if(direction==3 && ballHitEnd == false){

        help = (0.5*(newX-xPl)*tan(0.6)-(0.5 *pow((newX-xPl),2))
                / (2*pow(20,2)*pow(cos(0.6),2))+yPl)-yPl;
        moveByY = yPl - help;
        setY(moveByY);
        setPos(x(),y());

        // povecujemo x za 1.5 // incrementing x by 1.5
        newX = newX + 1.5;
        setX(x()-1.5);

        // ce je canon ball v vodi spremenimo sliko v splash sliko // if canon ball hits its final destination we change picture to a splash
        if(y() >= yPl+32){

            ballHitEnd = true;
            setPixmap(QPixmap(":/Images/Splash_2.png"));
        }
    }



    // slika ostane nekaj sekund nato se canon sporsti s pomnilnika // picture stays as a splash for couple of mikroseconds then we 
      delete the canon ball from memory
    if(ballHitEnd == true){

        splashLasting++;

        if(splashLasting == 15){
            game->scene->removeItem(this);
            CanonBallGone=true;
            delete this;
       }
    }
    // ce je canon ball sou izven scene ga sporstimo iz pomnilnika // if canon ball is out of the scene we remove it   //from the scene 
     and delete it
    if(x()<(0-30) || x()>game->getW()+30){
        qDebug() << "deleted canonball";
        game->scene->removeItem(this);
        delete time;
        CanonBallGone=true;
        delete this;
    }
}

Please if anyone has any ideas on how to fix this please let me know !!!

[SGaist]

Hi,

First thing before digging further: why does your cannon class know that much about its container and the rest ?
You should rather have a "game engine" that handle that kind of stuff. Why should a canon be responsible for its own deletion ?

You should also check this post about the use of delete this;

[MongKong]

@SGaist

I'm still a begginer at stuff like this and atm im making a simple game, i already figured out the problem to this so im going to mark this as solved but the thing is, i want to make sure that when my canon reaches its destination that it deletes itself and the best way to do that was to do it inside the class.... I believe.... and about the things i included, some of them probably aren't needed...

And i'll check the post u sent me, thank you !