static member initialisation for multiple objects

**kezman** · 04-13-2011

Hey,
I'm wondering what the best way to define the value of a static data member within a class is. The values I want to initialise the data to is the same throughout the entire life of the program, but is calculated on runtime. Currently I'm calculating this in the class constructor, but this is causing major cpu overheads when creating multiple objects of the class. Is there a better way to do this so the initialisation is only performed once? I'm either thinking I could move the calculation out of the constructor and into an initialisation function, but was hoping there was a neater way of doing this.
Any suggestions would be hugely appreciated,
Thanks,
Kieran

**manasij7479** · 04-13-2011

Static Data Members should be (re)declared outside the class declaration, because the memory for it is not allocated when inside the class.
For example..

Code:

class X
{
   static int x;
};
int X::x = 6;

**jinhao** · 04-13-2011

Using a nest class and its constructor

Code:

class T
{
	struct unique_tag
	{
		const int x;
		
		unique_tag()
			: x(calculate x)
		{	
		}
	};
	
private:
	static unique_tag unique_;
};

T::unique_tag T::unique_;

unique_ will be initialized before initialization of T. The nest class unique_tag is used for preventing programmer invoke the initializer of x.

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