How to : Static variable in inherited class

Question

class B {
 public:
   static int a;
};
class C:B {
};

I want to use a variable through any inherited classes but it has problem when I declare a.

B::B() {
  a=1;
};

Do I do it right ?
Thanks for reading and waiting for your comments.

// I miss semicolons which is not the error I'm talking . // This is an error when I try to delcare class GameState { public: static int a = 1; //... };

Error   7   error C2864: 'CGameState::a' : only static const integral data members can be initialized within a class    d:\my dropbox\work\#today\gdimario\gdimario\gamestate.h 18

I try to write a simple question which shows the problem I want instead of pasting my whole code.

Answer 1

You can use it directly like you did from both the derived and base class.

Perhaps your error is that you don't have semicolons at the end of your class declarations?

class B {
 public:
   static int a;
};

class C:B {
};

If you want to call it from an instance of C then you need to use public inheritance: (If nothing is specified private inheritance is assumed)

class C : public B {
};

To initialize a you need to do this (typically at the top of your corresponding .CPP file):

int B::a = 3;

Answer 2

You need to write in a CPP file:

int B::a;

And add the semicolons that Brad suggests. (Did you even compile your code? What did the compiler say?)

Answer 3

i think you ll get linker error. since you have not defined of the static variable in the .cpp file.

e.g.

//hearer file
class X{

 public : static int a ;

}
//impl file

int X::a(0);

....or...

For integral type you can also defined static variables when they are declared like:

class X{

 public : static int a  = 0;

}