CODEWITHSUNDEEP
c++classvariablesstatic
user1703993
user1703993

Reputation: 61

Defining static class pointer within another class

I have a class that has a static pointer to another class, which is a singleton. The problem that I seem to be getting though is that I cannot set the pointer from within the constructor of said class. Here is my current code:

class B;

class A
{
  public:
    A();
    ~A();
};


class B
{
  public:

    B();
    ~B();

    static A* a;
};

A::A() {
  A* B::a = this;
}

Now, the problem that I seem to be getting is that I cannot define B::a in the "current scope". In addition, the "this" pointer can only be used in a "nonstatic member function".

I think the problem has to do with defining the static class variable within another class function, but I am not sure.

Upvotes: 3

Views: 2593

Answers (2)

Murilo Vasconcelos
Murilo Vasconcelos

Reputation: 4827

You should define all static members outside the class declaration:

class B;
class A
{
public:
    A();
    ~A();
};


class B
{
public:

    B();
    ~B();

    static A* a;
};

A* B::a; // HERE

A::A()
{
    B::a = this; // and there was an error here too
}

Don't forget to define the other ctors/dtors.

Upvotes: 0

user500944
user500944

Reputation:

First of all, static class members have to be defined as well as declared. static A* a; in the body of class B is merely a declaration, and you need to define a. Note that every class member must have a single definition, that's why we usually define static members in the appropriate .cpp files for classes. Obviously, this happens outside of the class body. You also cannot define a static member in scope of a function.

So, move the definition of a outside of the constructor's scope, like this:

class B
{
public:

    B();
    ~B();

    static A* a;};

A* B::a = 0; // Good idea to set a default value for the pointer

Note, however, that the value of a will contain a 0 until at least one object of type A is created.

Upvotes: 3

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