C++ initializing const variable using static variable from another class

[Brutile]

If anyone knows C++, please help...

 

I'm trying to initialize a constant variable using a static variable from another class.

 

I want to assign:

// a.h

static const short worldHeight = 128;

 

To:

// b.h

static const short height = a::worldHeight;

 

So I can then do this:

// b.h

bool stuff[height];

 

But I get errors. Anyone know how to achieve this?

[Rick]

I don't use constants all that often but as far as I'm aware constants are basically literals (meaning you have to assign literals to them and not variables).

 

Why can't you just pass a::worldHeight to the stuff array? If you really want the height variable don't make it constant.

 

Also, if you ever get errors it's best to show us the errors in your post. It'll help us not have to guess.

[Brutile]

I can't pass it directly into the stuff array either.

 

The errors are:

1. use of undefined type 'a'

2. 'worldHeight': undeclared identifier

3. expected constant expression

 

Even though everything is declared at compile time.

 

Alternatively, If anyone knows how to make a class that holds variables that only need to be assigned once, and can be used for all classes. I'm only doing this so I don't need to make multiple instances of the same value.

[Brutile]

I kinda found a solution. I just declared the array as bool*** stuff; then did stuff*** = new bool**[num]; then looped and did stuff**[x] = new bool*[num]; then another loop and did stuff*[x][y] = new bool[num]; etc. It isn't as quick as declaring the array at compile time, but it works, so I'm happy

[catch22]

So, this is what defines are for generally. If your worldheight is going to be 128 no matter what, #define it in your particular header.

 

 

#define WORLDHEIGHT 128

 

(that's case sensitive btw. Most programmers caps their defines or use a way to recognize them. I prefer the old school 'k' prefix such as kWorldHeight -- all caps are fugly to my old eyes, but it's your style not mine!)

[catch22]

Alternatively, If anyone knows how to make a class that holds variables that only need to be assigned once, and can be used for all classes. I'm only doing this so I don't need to make multiple instances of the same value.

 

This is a very pythonic concept, actually. Since you can't really do globals in python (hallelujah), you can mimic the behavior by making a class that holds your predefined values, and then just import that class across your program files to access the "globals" which are just properties of a local class instance (at that point).

 

I still think #define is what you're after though. You'll want to make a header called like "globals.h" and use "#pragma once" at the top of the file, to avoid header fighting throughout your program. While non standard, just about everything respects it, and it's much simpler than old school header guards.

[Josh]

The simple answer is don't ever do this, ever.

 

Here is the long answer:

http://www.parashift.com/c++-faq/static-init-order.html

[Brutile]

catch22, you are a life saver! that #define works just how I wanted it to. Thank you and everyone else that helped.

I can now clean up my code a bit.

[Brutile]

Here's another question... can I access a #define from another class? Can it be accessed if I include the header or something?

[Rick]

That's what catch22 is talking about in his last post last paragraph.

 

 

// globals.h

 

#pragma once

 

#define MAP_HEIGHT = 128

 

 

 

Now in any file you need this just:

 

#include "globals.h"