Initialize pointer to array

Question

I am trying to initialize pointer to struct array in my class constructor but it do not working at all...

class Particles {
private:
 struct Particle {
 double x, y, z, vx, vy, vz;
 };
 Particle * parts[];
public:
 Particles (int count)
 {
 parts = new Particle [count]; // < here is problem
 }
};

• kassak: what is your problem?
• m0skit0: That's not a pointer to an array, that's an array of pointers to Particle. See this.
• juanchopanza: You could save yourself a lot of trouble by using an std::vector<Particle> instead of the dynamically allocated array.

Answer 1

Remove those [] from declaration. It should be

Particle *parts;

Using C++, you can use benefits of std::vector:

class Particles {
 // ...
 std::vector<Particle> parts;
 public:
 Particles (int count) : parts(count)
 {
 }
};

• juanchopanza: @balki no, because count is not a compile time constant. But std::vector<Particle> would do fine.

Answer 2

Particle * parts[];

This is an array of pointers. To initialise this, you would need to loop through the array, initialising each of the pointers to point at a dynamically allocated Particle object.

You probably want to just make parts a pointer:

Particle* parts;

The new[] expression returns a pointer to the first element of the array - a Particle* - so the initialisation will work just fine.

Answer 3

Try this:

class Particles {

private:

struct Particle {
 double x, y, z, vx, vy, vz;
};
Particle * parts;

public:

Particles (int count)
{
 parts = new Particle [count]; // < here is problem
}

};