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What! no static double constants in classes?

General and Gameplay Programming Programming

Started by CuppoJava October 22, 2005 02:26 PM

18 comments, last by cignox1 18 years, 6 months ago

CuppoJava

164

Author

October 22, 2005 02:26 PM

Hi, I just reached the classes chapter in my C++ book, and I'm shocked that I can't declare static double constants in a class. In java, i used the following everywhere...


class A
{
  final static double FACTOR = 12.35;
  final static int INT_FACTOR = (int)(FACTOR*100);
  final static int[] array = new int[INT_FACTOR];
}

How can I make an equivalent thing in C++?


class A
{
  static const double FACTOR = 12.35; //not allowed
  static const int INT_FACTOR = 1235; //but this is!?
  static const int array[INT_FACTOR];
}

Thanks a lot for your help. Honestly, I have to say that I don't like C++ very much, it seems quite inconsistent at times... Alas, the power of pointers comes at a heavy price. -Cuppo

Sneftel

1,788

October 22, 2005 02:27 PM

You can have them; you just need to initialize them where they're declared (in the source file), not where they're defined (in the header file).

omgomghilol

198

October 22, 2005 03:19 PM

Only integers and equivalent things (enumerations, etc.) can be initialized in the actual class.

moeron

326

October 22, 2005 03:19 PM

as sneftel said you just do it like this

// header fileclass foo{  public:    static const double bar;    static const float baz;}// in source fileconst double foo::bar = 12.5;const double foo::baz = 100.134;

moe.ron

CuppoJava

164

Author

October 22, 2005 03:35 PM

yea,
but then I can't access the INT_FACTOR variable in order to size my array. And because the INT_FACTOR variable depends on the constant double FACTOR there's no way to get that either.

Oluseyi

2,123

October 22, 2005 03:38 PM

Quote:Original post by Sneftel
You can have them; you just need to initialize them where they're declared (in the source file), not where they're defined (in the header file).

Isn't that backwards? The header contains the declaration; the source contains the definition.

doynax

850

October 22, 2005 03:39 PM

Quote:Original post by CuppoJava
yea,
but then I can't access the INT_FACTOR variable in order to size my array. And because the INT_FACTOR variable depends on the constant double FACTOR there's no way to get that either.

Ouch.. Then you're pretty much left with either defines or fixed point integers/enums.
At least I can't think of any other workaround.

CuppoJava

164

Author

October 22, 2005 03:42 PM

The only workaround that I can think of is to declare the constant double FACTOR globally ... or in a namespace. But then its just weird. If all my other variables are under class A, and then my FACTOR variable is found under a separate namespace ... pretty awkward..

Conner McCloud

1,135

October 22, 2005 03:44 PM

If FACTOR is a constant, then INT_FACTOR is a constant, then there's no problem. Just remove the math, and everything is OK.

CM

doynax

850

October 22, 2005 03:44 PM

Quote:Original post by CuppoJava
The only workaround that I can think of is to declare the constant double FACTOR globally ... or in a namespace. But then its just weird. If all my other variables are under class A, and then my FACTOR variable is found under a separate namespace ... pretty awkward..

That doesn't help either, there's no way you'll be able to make an array size out of it (at least I don't think you can..).

Quote:Original post by Conner McCloud
If FACTOR is a constant, then INT_FACTOR is a constant, then there's no problem. Just remove the math, and everything is OK.

CM

But it's a double so it isn't really a true compile time constant.

What! no static double constants in classes?

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