How to access private data members outside the cla

Question

This question already has an answer here:

• Can I access private members from outside the class without using friends? 24 answers

I have a class A as mentioned below:-

class A{
     int iData;
};

I neither want to create member function nor inherit the above class A nor change the specifier of iData.

My doubts:-

• How to access iData of an object say obj1 which is an instance of class A?
• How to change or manipulate the iData of an object obj1?

Note: Don't use friend.

Answer 1

You can't. That member is private, it's not visible outside the class. That's the whole point of the public/protected/private modifiers.

(You could probably use dirty pointer tricks though, but my guess is that you'd enter undefined behavior territory pretty fast.)

Answer 2

iData is a private member of the class. Now, the word private have a very definite meaning, in C++ as well as in real life. It means you can't touch it. It's not a recommendation, it's the law. If you don't change the class declaration, you are not allowed to manipulate that member in any way, shape or form.

Answer 3

Here's a way, not recommended though

class Weak {
private:
    string name;

public:
    void setName(const string& name) {
        this->name = name;
    }

    string getName()const {
        return this->name;
    }

};

struct Hacker {
    string name;
};

int main(int argc, char** argv) {

    Weak w;
    w.setName("Jon");
    cout << w.getName() << endl;
    Hacker *hackit = reinterpret_cast<Hacker *>(&w);
    hackit->name = "Jack";
    cout << w.getName() << endl;

}

Answer 4

It's possible to access the private data of class directly in main and other's function...

here is a small code...

class GIFT
{
    int i,j,k;

public:
    void Fun() 
    {
        cout<< i<<" "<< j<<" "<< k;
    }

};

int main()
{
     GIFT *obj=new GIFT(); // the value of i,j,k is 0
     int *ptr=(int *)obj;
     *ptr=10;
     cout<<*ptr;      // you also print value of I
     ptr++;
     *ptr=15;
     cout<<*ptr;      // you also print value of J
     ptr++;
     *ptr=20; 
     cout<<*ptr;      // you also print value of K
     obj->Fun();
}

Answer 5

In C++, almost everything is possible! If you have no way to get private data, then you have to hack. Do it only for testing!

class A {
     int iData;
};

int main ()
{
    A a;
    struct ATwin { int pubData; }; // define a twin class with public members
    reinterpret_cast<ATwin*>( &a )->pubData = 42; // set or get value

    return 0;
}

Answer 6

friend is your friend.

class A{
    friend void foo(A arg);
    int iData;
};

void foo(A arg){
     // can access a.iData here
}

If you're doing this regularly you should probably reconsider your design though.