Pong game bugging out - mayby pointer to class [closed] - c++

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get a problem with my code, this is just an extract from a larger piece of code involving OpenGL but still demonstrates the problem. It works without the collision detection call (col.detect()) - if you consider unbouncy walls working - but when I uncomment it the program breaks. Nothing seems to be wrong with the code itself it compiles just fine but doesn't work the way that I am expecting.
Thanks for all the help
Best Regards
collision.h
#pragma once
#include "Ball.h"
class collision
{
public:
collision();
collision(Ball ball);
void detect();
~collision();
private:
Ball *point;
};
Ball.h
#pragma once
class Ball
{
public:
Ball();
double getpx();
double getpy();
double getvx();
double getvy();
void setpx(const double px);
void setpy(const double py);
void setvx(const double vx);
void setvy(const double vy);
void update();
~Ball();
private:
double position[2] = { 0, 0 };
double velocity[2] = { 0.1, 0 };
};
collision.cpp
#include "collision.h"
collision::collision()
{
}
collision::collision(Ball ball)
{
point = &ball;
}
void collision::detect()
{
if (point->getpx() > 1 || point->getpx() < -1)
point->setvx(-point->getvx());
else if (point->getpy() > 1 || point->getpy() < -1)
point->setvy(-point->getvy());
}
collision::~collision()
{
}
Ball.cpp
#include "Ball.h"
Ball::Ball()
{
}
double Ball::getpx()
{
return position[0];
}
double Ball::getpy()
{
return position[1];
}
double Ball::getvx()
{
return velocity[0];
}
double Ball::getvy()
{
return velocity[1];
}
void Ball::setpx(const double px)
{
position[0] = px;
}
void Ball::setpy(const double py)
{
position[1] = py;
}
void Ball::setvx(const double vx)
{
velocity[0] = vx;
}
void Ball::setvy(const double vy)
{
velocity[1] = vy;
}
void Ball::update()
{
position[0] += velocity[0];
position[1] += velocity[1];
}
Ball::~Ball()
{
}
main.cpp
#include <iostream>
#include "Ball.h"
#include "collision.h"
using namespace std;
int main()
{
Ball tennis;
collision col(tennis);
while (true)
{
tennis.update();
col.detect();
cout << tennis.getpx() << endl;
cin.get();
}
return 0;
}

Answer 1

Below will cause your program to invoke Undefined Behavior when next you use point:
collision::collision(Ball ball)
{
point = &ball;
}
Where point is defined to be:
Ball *point;
The problem is that you are storing the address of an object with automatic storage-duration. ball will cease to exist after that function completes hence leaving point to point ot an invalid object.
You probably wanted to take the ball by reference; or better still use the services of std::unique_ptr or std::shared_ptr in your program.

Answer 2

Change the following code
collision::collision(Ball ball)
to
collision::collision(Ball& ball)
It should solve your problem. The problem was that Ball was a local variable whose address is no longer valid after the constructor exits. Solution : Send the object by reference and the address stored in the pointer will be of the object created in the main() function.