CODEWITHSUNDEEP
c++classprivate
이가원
이가원

Reputation: 39

How can i access to any data that is in private section of class?

#include <iostream>
#include <vector>

using namespace std;

class Test
{
private:
    int ID;
    string name;

public:
    Test(int ID, string name);
};

Test::Test(int ID, string name)
{
    this->ID = ID;
    this->name = name;
}

int main()
{
    vector<Test *> test_vect;

    Test *ptr = new Test(100, "John");

    test_vect.push_back(ptr);

    cout << ptr->ID << endl;

    return 0;
}

This is a simple code I'm trying.

I want to access to the data that I stored in vector.

I thought it would be accessible by using -> just like vector of struct but I can't. So I want to know how to load the data in class.

In addition, I thought sending data to heap section using new would make it accessible at any time I want regardless of whether it is private or public, but it seems like it is not possible.

Can you explain how it works?

(I don't even fully understand how class work, so detailed explanation would be very appreciated. Thx!)

Upvotes: 0

Views: 78

Answers (1)

Aaron Stanek
Aaron Stanek

Reputation: 584

A private variable cannot be accessed by code outside the class definition. (There are exceptions with friend)

ptr->ID does not work because main is outside the class definition.

This can be fixed by using a getter method.

#include <iostream>
#include <vector>

using namespace std;

class Test
{
private:
    int _ID;
    string _name;

public:
    int ID() {return _ID;}
    string name() {return _name;}
    Test(int param_ID, string param_name);
};

Test::Test(int param_ID, string param_name)
{
    _ID = param_ID;
    _name = param_name;
}

int main()
{
    vector<Test *> test_vect;

    Test *ptr = new Test(100, "John");

    test_vect.push_back(ptr);

    cout << ptr->ID() << endl;

    return 0;
}

The above example shows the getter methods ID() and name() which return the data members _ID and _name respectively.

ID() is allowed to access _ID because ID() is part of the class definition. name() is allowed to access _name because name() is part of the class definition.

Note: I would still consider this code to be flawed because it creates a new object on the heap, but does not delete it. You should also look up the keywords new and delete to see how they operate together.

Upvotes: 1

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