static variable in C++

[Yasushi Shoji]

hi all

i have a question with C++/pgcc 2.91.60 with following code.
hope C++ is not off topic :)

---from here----

#include <iostream.h>

class base {
public:
        base(void){counter++;}
        ~base(void){counter--;}

        int get_counter(void){
                return counter;
        }

private:
        static int counter; // (A)
};

int
main (void)
{
        base b;
        cout << b.get_counter() << endl;

        return 0;
}
-----till here----

trying to make a class with a static variable so that all objects
instantiated for that class can share one variable.
# hope i'm on the right road...

Question 1:
  how can i initialize counter at (A) to 0?
  i replaced (A) with
        static int counter = 0;
  
  and compiler said:
  "ANSI C++ forbids in-class initialization 
   of non-const static member `counter'"

Question 2;
  it seems that linker is not able to link object files from
  the source code:

bash$ g++ -Wall static.cpp
/tmp/ccPYx1jJ.o: In function `base::get_counter(void)':
/tmp/ccPYx1jJ.o(.base::gnu.linkonce.t.get_counter(void)+0x8): undefined reference to 
`base::counter'
/tmp/ccPYx1jJ.o: In function `base::~base(void)':
/tmp/ccPYx1jJ.o(.gnu.linkonce.t._._4base+0xd): undefined reference to `base::counter'
/tmp/ccPYx1jJ.o: In function `base::base(void)':
/tmp/ccPYx1jJ.o(.base::gnu.linkonce.t.(void)+0x5): undefined reference to 
`base::counter'
collect2: ld returned 1 exit status

regards,
--
yashi