accessing all the private members of a class c++

Question

I have created few class as below (Since I can not put my real class Here I have written few as just example )

 class One {
      private :
         char *link;
         int count 

        }


 class Two {
      private :
         char *link;
         int count 

        }

 class  Three :: public TWO  {
      private :
         char *link;
         int count ;
          One One_object;

        }

 int main() {

     Three test;
     cout << test.One_object.link ; // error becoz of accessing private member 

       }

Here what would be the best way access the private mebers , if it is only value to acess then I could have written a get method function to get the data .

But in my real class has many data members are protected .. Can you somebody through light on this ..

Have you ever heard of "friend" functions and classes, and/or access-members (aka. getters' and setters') ? — WhozCraig, Mar 02 '13 at 07:31
Like WhozCraig has already stated, a `friend` function (needs to be declared in the class) can access any private or protected member of the class, even though it's not a member of it. — Refugnic Eternium, Mar 02 '13 at 07:32
If you really *have* to, you can abuse the fact that arguments to explicit template instantiations ignore access control (`[temp.explicit]/12`) to access private or protected members. (For example, see [this](http://bloglitb.blogspot.com.au/2011/12/access-to-private-members-safer.html)). That said, `private` and `protected` are meant to be used to reduce the scope of variables to make the code simpler to understand. If you want variables that are accessible from anywhere, you should just make them `public`. — Mankarse, Mar 02 '13 at 07:41

score 1 · Answer 1 · answered Mar 02 '13 at 07:34

1

The private and protected member variables are meant to be accessed using member functions aka methods.

The methods which are meant to be used only internally from another method of the same class but not from outside should again be private or protected.

Choosing private vs protected depends on if you'll be inheriting from that class or not. It is recommended to use protected for all the members so that any class which inherits (may be in the future) from this class also benefits by getting access to these members.

And there are friend functions which let you access private or protected members from outside directly too.

answered Mar 02 '13 at 07:34

Tuxdude

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*Choosing private vs protected depends on if you'll be inheriting from that class or not. It is recommended to use protected for all the members so that any class which inherits (may be in the future) from this class also benefits by getting access to these members.* -- disagree. of course, it involves preference and how you structure your programs -- inheritance-heavy designs tend to have less flexibility in this regard. i think protected is the odd-duck, that private is a good default, and access should be granted only if truly required. i use protected far less than private and public. – justin Mar 02 '13 at 08:21

score 0 · Answer 2 · answered Mar 02 '13 at 08:28

In main, when you do test.One_object (you need to mark One_object as public though), you are getting the One object instance directly, but even then you can not access the private members of One because they are not visible from this context. So, you have two options:

1) If Class One is editable, you need to mark the variables you MUST access from main as public

OR

2) Make Three a friend class of One and write a getter function for each member variable of One_object in Three.

So, following option 2-

class One {
      private :
         char *link;
         int count;

      friend class Three;
};
class  Three : public Two  {
      private :
         char *link;
         int count ;
      public:
         One One_object;
         int get_One_object_count(){
            return One_object.count;
         }

};

I think you may reconsider the design of your classes as accessing the members from global context is not a very good design practice.

Read more about friend class and friend functions here.

accessing all the private members of a class c++

2 Answers2