can derived class access base class non-static members without object of the base class

Question

class base
{
public:
    int data;
    void f1()
    {
    
    }
};
class derived : base 
{
public :
     void f()
    {
        base::data = 44; // is this possible
        cout << base::data << endl;
    }
};

why does the below one shows a error

class base
{
public:
    int data;
    void f1()
    {
    
    }
};
class derived : base 
{
public :
     static void f()
    {
        base::data = 44; // this one shows a error
        cout << base::data << endl;
    }
};

i could not find the answer at any wedsites

`data` is a **instance** member variable. In the second code snippet, `f` is a *static* member function. There is no active instance in a static member function. Thus, there is no `data` because there is no instance. The difference between instance vs. static members is covered in *any* remedial text on the C++ language. — WhozCraig, Jan 18 '22 at 04:31
What would you expect it to mean to be able to access a non-static member of the class without an object of that class? Given that you understand what the difference is between non-static and static members is, why would you expect the second version to work at all? — Nathan Pierson, Jan 18 '22 at 04:33
`base::data = 44;` is actually `this->base::data = 44;` (as `data` is not `static`). and in `static` method as`f`, you cannot use `this`. — Jarod42, Jan 18 '22 at 09:20

score 3 · Accepted Answer · answered Jan 18 '22 at 04:36

In your 1st example

class derived : base 
{
    void f()
    {
        base::data = 44;
    }
};

f() is not-static. It works on an object of derived, which includes an object of base. So, base::data = 44; is equivalent to data = 44; and it accesses the member of the object.

In the 2nd example

class derived : base 
{
    static void f()
    {
        base::data = 44;
    }
};

function f() is static, so it does not have access to any object. There, base::data = 44; could mean static data member of base. But because data is non-static, the expression is ill-formed.

can derived class access base class non-static members without object of the base class

1 Answers1