firework opengl - c++

Question

I'm trying to create a firework with OpenGL (I must put 100 particles in the position (0,0,0)) with the function
Particle *p[100];
void Build()
{
for (int i = 1; i <= 100; i++)
{
p[i]->pos.x = 0.0;
p[i]->pos.y = 1.0;
p[i]->pos.z = 5.0;
p[i]=AddParticle(*p[i]);
}
}
but I get the following error:
Unhandled exception at 0x771b15de in ass.exe: 0xC0000005: Access violation writing location 0x00000000.
this is the rest of the code:
class Particle
{
public:
Vector3 pos; // current position
Vector3 vel; // velocity
Vector3 restPos; // rest (initial) position
Vector3 oldPos; // previous position
Vector3 acc; // acceleration
Particle()
{
oldPos = restPos = pos = Vector3(0, 0, 0);
Init();
}
Particle(float x, float y, float z)
{
oldPos = restPos = pos = Vector3(x, y, z);
Init();
}
Particle(const Vector3 & _p)
{
oldPos = restPos = pos = _p;
Init();
}
void Init()
{
acc = Vector3(0, 0, 0);
vel = Vector3(0, 0, 0);
}
void Update(const float & time_step)
{
Verlet(time_step);
}
// integration step with Verlet
void Verlet(const float & time_step)
{
Vector3 temp = pos;
pos += vel * time_step + acc * time_step * time_step ;
vel = (temp - oldPos) / time_step;
oldPos = temp;
}
};
# endif // _PARTICLE__
using namespace std;
class ParticleSystem
{
vector<Particle> _particles; // the particles
Vector3 m_vGravity; // gravity force applied to the particles system
float m_fTimeStep; // time step
Vector3 attractor;
public:
ParticleSystem()
{
m_vGravity = Vector3(0, -9.81f, 0);
m_fTimeStep = TIME_STEP;
attractor = Vector3(0, 0, 0);
}
void Reset()
{
_particles.clear();
}
// accessing the fields
void SetGravity(Vector3 g) { m_vGravity = g;}
void SetTimeStep(float ts) { m_fTimeStep = ts;}
// adding a particle
Particle* AddParticle(Particle _p)
{
_particles.push_back(_p);
return &(_particles.back());
}
void Build()
{
for (int i = 1; i <= 100; i++)
{
Particle p;
p.pos.x = 0.0;
p.pos.y = 1.0;
p.pos.z = 5.0;
p[i]=AddParticle(p);
}
}
void Draw()
{
// draw round points
glPointSize(4.f);
glEnable(GL_POINT_SMOOTH);
glAlphaFunc(GL_GREATER,0.5f);
glEnable(GL_ALPHA_TEST);
glEnable(GL_BLEND);
glDisable(GL_TEXTURE_2D);
glDisable(GL_LIGHTING);
// draws the particles
glBegin(GL_POINTS);
glColor3f(1.f, 0.f, 0.f);
vector<Particle>::iterator pIt;
for(pIt = _particles.begin(); pIt != _particles.end(); pIt++)
{
Vector3& pos = pIt->pos;
glVertex3f(pos.x, pos.y, pos.z);
}
glEnd();
glEnable(GL_LIGHTING);
}
#endif // __PARTICLE_SYSTEM__

Answer 1

You've declared an array of pointers to Particles, but not actually allocated any of them.
(and as someone else points out, arrays are 0 indexed, not 1 - so your loop is out by 1 anyway)
It's not entirely clear how this is supposed to work, as you seem to be filling in a particle structure, which you pass to AddParticle(), which returns a pointer to a particle, which you put back in the array you've already tried to reference.
Looking at your code, you probably just need something like:
void Build()
{
for (int i = 1; i <= 100; i++)
{
AddParticle(Particle(0.f, 1.f, 5.f));
}
}
No array needed as the particle class looks after the particles.

Answer 2

i think it's because the array goes from 0 to 99...not 1 to 100 .
Change the for statement to for (int i = 0; i < 100; i++) and remember the array starts with a 0
Also i think i know what you're trying to do..try this code:
void Build()
{
Particle p[100];
for (int i = 0; i < 100; i++)
{
p[i].pos.x = 0.0;
p[i].pos.y = 1.0;
p[i].pos.z = 5.0;
AddParticle(p[i]);
}
}