Assistance needed with pointer arrays

[DethRaid]

As the title suggests, I am trying to use a pointer as an array in my code but it's not working. I've read the tutorials on this site and a few others about using pointers as arrays, and as far as I can tell I'm doing things correctly, save that I keep getting an error. My pointer is declared like this:

 #define ASTEROID_ARRAY_LENGTH 4
Asteroid *asteroids = new Asteroid[ASTERIOD_ARRAY_LENGTH];

void init()
{
    for( int i = 0; i < ASTERIOD_ARRAY_LENGTH; i ++ )
         asteroids[i]->spawn( (float)rand(), (float)rand() );
}

init() is called at the beginning of my WinMain function, as I'm coding a Windows GUI application.

The error message I get is this: error: base operand of '->' has non-pointer type 'Asteroid'. I am using Code::Blocks on 64-bit Windows 7, if any of that matters.

I have also tried to use malloc() and calloc() to allocate memory for my array, both with various errors revolving around the compiler not finding the Asteroid(void*) constructor. As you may have guessed, I have no clue how to fix that error either. Asteroid.h looks like this:

#ifndef ASTEROID_H
#define ASTEROID_H

#include <math.h>
#include <windows.h>
#include <gl/gl.h>
#include <iostream>
#include <fstream>
#include <string>
#include "Rect.h"

class Asteroid
{
     public:
          Asteroid();
          Asteroid( void* );
          Asteroid( int );
          void spawn( float, float );
          void draw();
          void move();
          void checkIfOutside();
          void enable();
          void takeDamage( int );
          Rect getRect();
          void die();
     private:
          float x, y, red, green, blue, theta, xSpeed, ySpeed, rSpeed;
          int health, maxHealth;
          bool enabled;
          //string fileName( "asteroiddebugger" );
          std::ofstream debug;
          Rect rect;
          Utility utility;
};
#endif 

All functions declared in that file have an implementation in Asteroid.cpp.

Undoubtedly some of you will suggest that I just use an array. For what I'm doing, an array would work extremely well. The thing is, though, I'm creating this program as a learning experience, so that I may expand my knowledge of the C++ language. Arrays would work fine, but wouldn't teach me anything.

[JLBorges]

for( int i = 0; i < ASTERIOD_ARRAY_LENGTH; i ++ )
         // asteroids[i]->spawn( (float)rand(), (float)rand() );
         asteroids[i].spawn( (float)rand(), (float)rand() ); 

[viliml]

as JLBorges aid, use the dot operator instead of the arrow one. The arrow operator is used to get a member of a pointer, but the [] operator return the type of the array, not a pointer to it, so you have to use the dot operator which returns the direct member.

[DethRaid]

So I'd use the arrow operator with a single pointer, and the dot operator when I'm using my pointer as an array?

It compiles, but the program crashes before anything is drawn. That might be as issue with my modeless dialog, though... Those things are extremely laggy.

[rollie]

The 'arrow operator' (structure dereference operator, really) is typically used to call a member function of an object from a pointer. It handles the dereference for you, so you don't need to manually dereference a pointer to access member functions like (*myPointer).SomeMethod();. The array subscript has a similar property, in that when used on a pointer it will return the the subscripted object in that array, not a pointer to that object. Since the dereference is done for you, you can't use the "->" operator, as you are no longer working with a pointer, and instead use the structure reference operator "." as in someArray[i].SomeMethod();

[DethRaid]

Alright, I understand now. Thanks.

[bluecoder]

thanks rollie , that helped me to clear the concept to some extend .