Good $daytime,
> Date: Wed, 20 Jan 1999 21:57:48 -0500
> From: Yasushi Shoji <[EMAIL PROTECTED]>
> To: [EMAIL PROTECTED]
> Subject: summary: static variable in C++
> case 1:
> if you declare static variable outsize of the class,
> that means the variable is global. so that, it is possible
> to access the static variable from outsize of a object.
> static int counter = 0;
> class base {
> public:
> base(void) {counter++;}
> ~base(void){counter--;}
> int get_counter(void) {return counter;}
> };
> int main(void) {
> base b;
> counter += 1; // this is ok;
> cout << b.get_counter(); // this prints 2
> }
This works indeed, but brings another small but fundamental problem:
o Namespace pollution: from now on, you can't have another object
named 'counter' without trouble. This may be painful if your
software is a library.
> case2:
> you should initialize(or define?) static variable
> outside of the class declaration.
Should you define it? Yes. Should you initialise it? Perhaps.
Consider an example.
class base {
private:
static int counter;
public:
base(void) {counter++;}
~base(void){counter--;}
int whatever(void);
int get_counter(void) {return counter;}
};
You may never implement base::whatever() -- as long as you don't use
it. If you do, you should put somewhere:
int base::whatever()
{
...
}
The same applies to base::counter. You write
int base::counter;
or
int base::counter = 0;
'static int counter' and 'int whatever(void)' are _declarations_, used
primarily for type checking.
'int base::counter' and 'int base::whatever()' are _definitions_ that
actually create such object.
'= 0' is a way to statically _initialize_ a variable. One can also
think of '{ ... }' being sort of "initial value" for a function body :)
> case3:
> because, in my example, static variable is private,
> you need a static function if you want to access to
> that static variable without an object.
Sure.
Regards,
Willy.
--
"No easy hope or lies | Vitaly "Willy the Pooh" Fedrushkov
Shall bring us to our goal, | Information Technology Division
But iron sacrifice | Chelyabinsk State University
Of Body, Will and Soul." | mailto:[EMAIL PROTECTED] +7 3512 156770
R.Kipling | http://www.csu.ac.ru/~willy VVF1-RIPE
