Qt5 C++ Application Crashes for unknown reasons [closed] - c++

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I am really struggling with that strange bug for some time. My application crashes even before widgets are shown (but window itself is shown). Here is my code:
main.cpp
#include "mainwindow.h"
#include <QApplication>
#include <QTimer>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.setWindowTitle("Snake");
w.resize(500, 500);
w.show();
QTimer* timer = new QTimer();
while(!w.checkCollision())
{
if(timer -> isActive() == false)
{
w.play();
timer -> start(1);
}
}
return a.exec();
}
mainwindow.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QPainter>
#include <QKeyEvent>
#include <QDebug>
#include <snakeclass.h>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
Snake snake;
void paintEvent(QPaintEvent*);
void keyEvent(QKeyEvent* keyevent);
void move();
bool checkCollision();
void play();
~MainWindow();
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QPainter>
#include <QPainterPath>
#include <QKeyEvent>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
}
void MainWindow::paintEvent(QPaintEvent*)
{
QPainter painter(this);
// Draw black background.
painter.drawRect(0, 0, 500, 500);
painter.fillRect(0, 0, 500, 500, Qt::black);
for(unsigned int i = 0; i < snake.getLength(); i++)
{
// Draw green snake's body.
painter.setPen(Qt::green);
painter.setBrush(Qt::green);
// If i = 0, so if we are drawing snake's head.
if(i == 0)
{
// Draw red head.
painter.setPen(Qt::red);
painter.setBrush(Qt::red);
}
painter.drawEllipse((snake.getDot(i)).x, (snake.getDot(i)).y, 10, 10);
}
}
void MainWindow::keyEvent(QKeyEvent* keyevent)
{
if(keyevent -> key() == Qt::Key_Left)
{
if(snake.getDirection() != Snake::Direction::RIGHT)
{
snake.setDirection(Snake::Direction::LEFT);
}
}
else if(keyevent -> key() == Qt::Key_Right)
{
if(snake.getDirection() != Snake::Direction::LEFT)
{
snake.setDirection(Snake::Direction::RIGHT);
}
}
else if(keyevent -> key() == Qt::Key_Up)
{
if(snake.getDirection() != Snake::Direction::DOWN)
{
snake.setDirection(Snake::Direction::UP);
}
}
else if(keyevent -> key() == Qt::Key_Down)
{
if(snake.getDirection() != Snake::Direction::UP)
{
snake.setDirection(Snake::Direction::DOWN);
}
}
}
void MainWindow::move()
{
for(unsigned int i = snake.getLength(); i > 0; i--)
{
snake.editDot((snake.getDot(i - 1)).x, (snake.getDot(i - 1)).y, i, (snake.getDot(i - 1)).direction);
}
if(snake.getDirection() == Snake::Direction::UP)
{
if(int(snake.getDot(0).y - 10) < 0)
{
snake.editDot((snake.getDot(0)).x, 500, 0, snake.getDirection());
}
else
{
snake.editDot((snake.getDot(0)).x, (snake.getDot(0)).y - 10, 0, snake.getDirection());
}
}
else if(snake.getDirection() == Snake::Direction::DOWN)
{
if(((snake.getDot(0)).y + 10) > 490)
{
snake.editDot((snake.getDot(0)).x, 0, 0, snake.getDirection());
}
else
{
snake.editDot((snake.getDot(0)).x, (snake.getDot(0)).y + 10, 0, snake.getDirection());
}
}
else if(snake.getDirection() == Snake::Direction::RIGHT)
{
if(((snake.getDot(0)).x + 10) > 490)
{
snake.editDot(0, (snake.getDot(0)).y, 0, snake.getDirection());
}
else
{
snake.editDot((snake.getDot(0)).x + 10, (snake.getDot(0)).y, 0, snake.getDirection());
}
}
else if(snake.getDirection() == Snake::Direction::LEFT)
{
if((int((snake.getDot(0)).x) - 10) < 0)
{
snake.editDot(500, (snake.getDot(0)).y, 0, snake.getDirection());
}
else
{
snake.editDot((snake.getDot(0)).x - 10, (snake.getDot(0)).y, 0, snake.getDirection());
}
}
}
bool MainWindow::checkCollision()
{
for(unsigned int i = 0; i < snake.getLength(); i++)
{
for(unsigned int j = 0; j < snake.getLength(); j++)
{
if((i != j) && ((snake.getDot(i)).x == (snake.getDot(j)).x) && ((snake.getDot(i)).y == (snake.getDot(j)).y))
{
return true;
}
}
}
return false;
}
void MainWindow::play()
{
//move();
update();
}
MainWindow::~MainWindow()
{
delete ui;
}
snakeclass.h
#ifndef SNAKECLASS
#define SNAKECLASS
#include <vector>
class Snake
{
public:
enum class Direction
{
LEFT,
RIGHT,
UP,
DOWN
};
// Dot is a part of the snake.
struct dot
{
unsigned int x;
unsigned int y;
// Number of the dot (head is 0).
unsigned int dotNumber;
// Direction of the particular dot.
Direction direction;
};
unsigned int getLength();
unsigned int getScore();
unsigned int getSpeed();
Direction getDirection();
dot getDot(unsigned int dotNumber);
void setLength(unsigned int length);
void setScore(unsigned int score);
void setSpeed(unsigned int speed);
void setDirection(Direction direction);
// Returns new dot's dotNumber.
unsigned int newDot();
void editDot(unsigned int x, unsigned int y, unsigned int dotNumber, Direction direction);
private:
unsigned int length = 3;
unsigned int score = 0;
unsigned int speed = 1;
Direction direction = Direction::RIGHT;
std::vector <dot> dots = {dot {250, 250, 0, Direction::RIGHT},
dot {240, 250, 1, Direction::RIGHT},
dot {230, 250, 2, Direction::RIGHT}};
};
#endif // SNAKECLASS
snakeclass.cpp
#include "snakeclass.h"
unsigned int Snake::getLength()
{
return length;
}
unsigned int Snake::getScore()
{
return score;
}
unsigned int Snake::getSpeed()
{
return speed;
}
Snake::Direction Snake::getDirection()
{
return direction;
}
Snake::dot Snake::getDot(unsigned int dotNumber)
{
return dots.at(dotNumber);
}
void Snake::setLength(unsigned int length)
{
this -> length = length;
}
void Snake::setScore(unsigned int score)
{
this -> score = score;
}
void Snake::setSpeed(unsigned int speed)
{
this -> speed = speed;
}
void Snake::setDirection(Snake::Direction direction)
{
this -> direction = direction;
}
unsigned int Snake::newDot()
{
dot newDot;
newDot.dotNumber = dots.size();
dots.push_back(newDot);
length ++;
return newDot.dotNumber;
}
void Snake::editDot(unsigned int x, unsigned int y, unsigned int dotNumber, Snake::Direction direction)
{
for(unsigned int i = 0; i < dots.size(); i++)
{
if((dots.at(i)).dotNumber == dotNumber)
{
dots.at(i).x = x;
dots.at(i).y = y;
dots.at(i).direction = direction;
}
}
}
I am new to Qt5 and this is my first project involving painter and keyboard events. Could you help me to figure out what the problem in the code above is? Thank you for all the answers!

Answer 1

My application crashes even before widgets are shown (but window itself is shown).
It doesn't crash. In main.cpp there is an infinite loop in which some results are expected, namely !w.checkCollision(), but since there is no event loop running in main.cpp nothing happens and the programs hangs there waiting in vain.
As an answer to your question, in order to see the widgets add QApplication::processEvents(); in the following way:
while(!w.checkCollision())
{
QApplication::processEvents();
if(timer -> isActive() == false)
{
w.play();
timer -> start(1);
}
}
However, with this approach you will face further problems. So I would strongly advise you to take a look at the examples in the Qt Creator in order to see which is the correct way of using the library as thought by the Qt developers.