Forced to use constants

Hi,

I'm having a problem with being forced to use constants in my program.

At one moment, I try to do

AUX_RGBImageRec *TextureImage[nb_textures];

and my compiler complains that it was "expecting a constant expression". The problem is that I cannot define a constant with the right value because I don't know what that value is before runtime.

nb_textures is a member variable of a class and is set when the class is instantiated. I tried stuff like defining a constant in my class and initializing it to that same value but the compiler isn't dumb enough to be satisfied with that. I guess it follows the chain and sees that ultimately nb_textures is not a constant.

So I'm asking you guys how I can trick the compiler into thinking that it's given a constant. It's probably something really simple but I'm not really experienced and I am slowly learning the stuff.

Thanks in advance

When you create arrays statically, then you need constants. You can dynamically allocate your arrays:

Code:

---

AUX_RGBImageRec* TextureImage = new AUX_RGBImageRec[nb_textures];

---

and then deallocate when you are done

Code:

---

delete[] TextureImage;

---

A nicer, safer option, however, would be to use std::vector.

Code:

---

#include <vector>

... etc ...
std::vector<AUX_RGBImageRec> vec;
vec.push_back( ... an AUX_RGBImageRec here ... );

---

Then, you do not need to worry about deallocation. Also, you can force the vector to set aside enough space by calling the reserve(int) member function, taking the desired size as a parameter.

Thanks for the prompt reply. That made sense so I tried it but came up with a new error:

Code:

---

binary '=' : no operator found which takes a right-hand operand of type 'AUX_RGBImageRec *' (or there is no acceptable conversion)

---

This happens when I do

Code:

---

        AUX_RGBImageRec* TextureImage = new AUX_RGBImageRec[nb_textures];
        memset(TextureImage, 0, sizeof(void *) * nb_textures);

        int nb_true_status = 0;

        for( int i = 0; i < nb_textures; i++ )
        {
                if(TextureImage[i] = LoadBMP(TEXTURE_NB(i)))
                {
                        nb_true_status++;
                }
        }

---

The error happens on the line that has the if statement. My guess is that there's a problem with the type but I've been working on this for so many hours that I can't think clearly anymore. The original

Code:

---

AUX_RGBImageRec *TextureImage[nb_textures];

---

seems to me like it defines an array of pointers to AUX_RGBImageRec objects if I'm not mistaken. The code that was suggested on the second post

Code:

---

AUX_RGBImageRec* TextureImage = new AUX_RGBImageRec[nb_textures];

---

doesn't seem to create the same in my understanding. I can't really follow what it's supposed to create. As soon as I got this fixed, I'm stopping for today ;)

*EDIT*
I tried using

Code:

---

AUX_RGBImageRec * TextureImage = (AUX_RGBImageRec*) malloc (sizeof(AUX_RGBImageRec *)*nb_textures);

---

but it gives the same mistake. Is it possible then that the error lies elsewhere?

Thanks

Is the first line of you code ("AUX_RGBImageRec* TextureImage = new AUX_RGBImageRec[nb_textures];") the line the error is complaining about? How is AUX_RGBImageRec defined? What does LoadBMP() return?

Oh I just reread your last post and see what you're saying. AUX_RGBImageRec is defined as a pointer and you are attempting to create an array of those pointers (a 2D array).

For a 2D array your syntax should look something like this:
YourPtrType *array = new YourPtrType[count];
where YourPtrType could be defined as something like:
typedef YourType* YourPtrType;

*EDIT* Oops looks like I started writing right before you answered. Well your solution fixes my problem. It makes a lot of sense.

Thanks a lot

Okay. You need to use a two-dimensional array. Each element of your array must be a pointer.

Code:

---

AUX_RGBImageRec **TextureImage = new AUX_RGBImageRec*[nb_textures];

---