How to declare a member variable that is only visible to one class method per class instance?-CodePudding

Is there a way to declare member4 that only visible to Function1 and it is not shared by all instances?

class Test
{
  public:
    void Function1()
    {
        ???? int member4 //visble to Function1   (single instance)
    }
    void Function2()
    {
        static int member3;// visble to Function2  (all instances)
    }

  private:
    int member1; // visble to Function1 and Function2  (single instance)
    static int member2;//visble to Function1 and Function2 (all instances)

};

CodePudding user response：

Your question looks like an XY Problem. Anyway, here are two possible solutions.

First, you could wrap the field into a class and declare the method as a friend:

class Test {
public:
    // Don't forget to init Data:
    Test();

    void function1();
    void function2();

private:
    class Data;
    Data *data;
};

class Test::Data {
    int get() { return 42; }
    friend void Test::function1();
};

void Test::function1() {
    int secretData = data->get();
}

void Test::function2() {
    // Will not compile:
    // int secretData = data->get();
}

This solution smells. Much better would be to extract the entity that has this secret member into a separate class:

class AnotherEntity {
public:
    void function1() {
        // use secretData here;
    }

private:
    int secretData;
};

class Test : public AnotherEntity {
public:
    void function2();
private:
};