Thread: hi, is it possible to access the prviate members of a class using a friend function?

Straight from Sams in 21 days.....

"If you want to expose your private member data or functions to another class, you must declare that class to a be a friend. This extends the interface of your class to include the friend class."

Remember just because you declare a class to be a member of another doesn't mean that class can access the other classe's method.

For example, I declare you to be my friend, I decide to tell you might secret, that's my business I don't have to have access to your secrets.

Code:

class afriend { 
        friend void alterdata(); 
    private: 
        int data; 
}; 

void alterdata() 
{ 
afriend::data = 5; 
}

Remember that friend functions are NOT members of the class. That's why the alterdata function definition is not written:

afriend::void alterdata()
{
data = 5;
}

But they DO have access to all members of the class. You just have to make sure you qualify those members with the class name.

[EDIT]
Just corrected a small mistake. It's ok now.
[/EDIT]

Originally posted by mickey
no wait..., i've suddenly thought about this

Considering I wrote that about a week ago, I would say your "suddenly" is way slow

But nonetheless you are right, of course. It just happens I only had your example to go through. Still, I went on the err side because i didn't notice the following:

What I wrote can be done when the data member (private or not) was declared as static. These kind of data members exist even before any object gets created.

Otherwise, you should pass the object as an argument of the function.

void alterdata(afriend myfriend)
{
myfriend.data = 5;
}

For this minimalist example you give there is in fact no need to declare the function as friend. You should put it on the public section of your class and it becomes a member function of the class.