How to check whether an index in an array is empty - c++

Question

I'm making a small OpenGL program for my intro to C++ class in Uni. I have a program that is complete but I want to change it up a bit to make it more unique. I have a Cube class:
class Cube {
public:
Cube(Mesh* mesh, Texture2D* texture, float x, float y, float z);
~Cube();
void Draw();
void Update(float rSpeed);
Vector3 position;
private:
GLfloat rotationSpeed;
Vector3 rotationVector;
Mesh* _mesh;
Texture2D* _texture;
};
I then create an array of type Cube:
Cube* cubes[CUBE_AMOUNT];
I then fill each index of this array with data to draw the cube on screen later in the program:
for (int i = 0; i < CUBE_AMOUNT; i++) {
float x = ((rand() % 400) / 10.0f) - 20.0f;
float y = ((rand() % 200) / 10.0f) - 10.0f;
float z = -(rand() % 1000);
if (i % 2 == 1) {
cubes[i] = new Cube(cubeMesh, textureStars, x, y, z);
}
else {
cubes[i] = new Cube(cubeMesh, texturePenguins, x, y, z);
}
}
With this new thing I want to add to the program, I want to check whether an index of cubes[] has been filled with the data yet. However I keep getting exceptions when running. I have tried to check whether cubes[i] is equal to nullptr, and tried checking whether it is NULL too, but neither seem to match.
Sorry for any errors in terminology that I used. New to C++, and having come from only doing Python before this, it is confusing!
Solution:
When I create the array, I changed it to Cube* cubes[CUBE_AMOUNT] = { NULL }, and now when checking the array, cubes[i] == NULL!

Answer 1

If cubes is not a global variable, you can use:
Cube* cubes[CUBE_AMOUNT] = {};
to initialize all the elements to nullptr.
You can also use:
std::vector<std::unique_ptr<Cube>> cubes(CUBE_AMOUNT);
to remove the burden of having to deallocate dynamic memory in your code.
In either case, can use:
if ( cubes[index] )
{
// Got a valid pointer. Use it.
}

Answer 2

Your cubes variable is not automatically initialized with null_ptr's. Until you either fill it with null_ptr's or good pointers it initially points to random garbage.

Answer 3

I think this would work
//This bit should check if theres anything stored currently.
cout << "\nWhich Slot would you like to store the informaton in ?(1-10)";
cin >> i;
i--;
if (information[i] != NULL){
// Already written
cout << "THERES SOMETHING HERE";
}
else{
cout << "\nEMPTY!!!!!!!!!";
}