Question

I used the Fireworks init function to store a particle into the particles vector class.
And when I try to retrieve the count of the particles vector in the update() function, the particles vector is empty. Why?

Fireworks.cpp class:

void Fireworks::init(){
    float x = randf();
    float y = - 1 * randf(); //Going UP
    float z = randf();

    Particle part(position,Vector3f(x,y,z), color, randInt(1,50));
    particles.push_back(part);
}

bool Fireworks::update(){
    Particle particle;
    int count = particles.size(); //Total num of particles in system
    cout << particles.size() << " ";
}

class Fireworks: public ParticleSystem {
private:
  void init();

public:

  Fireworks(Vector3f pos, Vector3f col) {
    position = pos;
    color = col;
    init();
  }

  virtual bool update();
};

particlesystem.h

class ParticleSystem {
protected:
  vector<Particle> particles;

public:
  //virtual Particle generateParticle();
  virtual bool update(){return false;};
};

main.cpp

ParticleSystem *PS;
int main( int argc, char *argv[] ) {
  PS = &Fireworks(Vector3f(0,0,0), Vector3f(200,0,255));
  glutIdleFunc(move);
}

void move()
{
   PS->update();       
}

Answer 1

PS = &Fireworks(Vector3f(0,0,0), Vector3f(200,0,255));

This introduces undefined behavior. The right hand side creates a temporary, which will be deleted as soon as that full expression is over (i.e. right after the ;). PS will point to a deleted object after that line – doing anything with it is undefined behavior.

Use new.

PS = new Fireworks(Vector3f(0,0,0), Vector3f(200,0,255));

Also, you must return from all functions that are declared as returning something (non-void). It doesn’t matter if they’re virtual or not.