Using a static member variable

Question

Hello in my class Bullet I declare active as false when the bullet isn't active and true when it is. In my other class that isn't connected to my Bullet class in any way I want to use the bool member active and change it, how can I do that?

Im getting the error

Error 18 error LNK2001: unresolved external symbol "public: static bool Bullet::active" (?active@Bullet@@2_NA) C:\Skolarbete\Programmering i C++\ProjectTemplate\ProjectTemplate\Alienrow.obj ProjectTemplate

Declaration: static bool active;

When I use it: Bullet::active = false;

Im quite new too C++ so don't hate! Appreciate all the help I can get :D

Answer 1

A static variable inside a class is actually an external declaration. You still need the variable definition. This is similar to C external variables.

So in the .h file:

class Bullet
{
public:
    static bool active;
};

and in the .cpp file, at global scope:

bool Bullet::active = false;

The lack of the variable definition (not declaration) is deduced because your error message actually comes from the linker, not the compiler.