Protected...?

Okay...I that it is possible to do the following...

Code:

---

class Person
{
  public:
  int var1;
  int var1;
};

---

but what is the point of doing this altered version...

Code:

---

class Person
{
  protected:
  int var1;
  int var2;
};

---

I know what it does (well, I think that it makes the class members after "protected:" unable to be accesed...correct me if I am wrong), but what is the point of doing it?

Thanks
-Chris

protected is the same as private (no direct access from outside the class) but protected class members can be accessed by derived classes eg. -

Code:

---

#include <iostream>

using namespace std;
 
class Person
{
protected:
        int var1;
        int var2;
};

class Adult : public Person
{
protected:
        int var3;
public:
        void SetVar1(int i){var1=i;} //access Person member variable
        int GetVar1(){return var1;}
};

int main()
{
        Adult me;
        me.SetVar1(27);
        cout << me.GetVar1();
        return 0;
}

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Quote:

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Originally posted by zen
protected is the same as private (no direct access from outside the class) but protected class members can be accessed by derived classes

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Protected members can also be accessed by friend functions. I don't know if friend functions are used much in the real world, our instructor doesn't like them, but the Deitel text uses them for overloaded << operators on classes.

Quote:

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Protected members can also be accessed by friend functions. I don't know if friend functions are used much in the real world, our instructor doesn't like them, but the Deitel text uses them for overloaded << operators on classes.

---

As can private members. Friend functions are necessary when you want to use the member function of an object on the right of a binary expression.

If you overloaded the << operator for ouput inside the class (rather than as a friend function), you'd have to do something like -

Code:

---

class Adult
{
protected:
        int var1;
public:
        void SetVar1(int i){var1=i;}
                ostream& operator<<(ostream& os){return os << var1;}
};

int main()
{
        Adult me;
        me.SetVar1(27);
        me << cout;
        return 0;
}

---

as the Adult object has to be on the left. If you use a friend function you can put the ostream of the left -

Code:

---

class Adult
{
private:
        int var1;
public:
        void SetVar1(int i){var1=i;}
        friend ostream& operator<<(ostream& os,Adult& a);
};

ostream& operator <<(ostream& os,Adult& a)
{
        return os << a.var1;
}

int main()
{
        Adult me;
        me.SetVar1(27);
        cout << me;
        return 0;
}

---