c++ how to access variable from member function?

Question

I have a problem. I want to operate with single element of an array, which is generated in member function, but it doesn´t work. Here is my code:

    using namespace std;

    class Example
    {
    public:
        int *pole;
        void generate_pole();
    };

    void Example::generate_pole()
    {
        int *pole = new int [10];

        for (int i = 0; i < 10; i++)
        {
            pole[i] = i;
        }
    }

    int _tmain(int argc, _TCHAR* argv[])
    {
        Example reference;

        reference.generate_pole();

        cout << reference.pole[1] << endl;          //there is the problem

        system("pause");
        return 0;
    }

How can I get an access to the element? And where is the real problem? Thank you!

You are shadowing the member variable here: int *pole = new int [10]; change that part to pole = new int [10]; — πάντα ῥεῖ
– πάντα ῥεῖ, Commented Sep 10, 2015 at 12:22

Bathsheba · Accepted Answer · 2015-09-10 12:27:20Z

2

int *pole = new int [10]; is creating an identically named variable pole in local scope. This is shadowing the member variable.

A fix, drop the int* from the errant line: pole = new int [10];

That said, I'd be inclined to use a constructor to set the member variable in this case: certainly you should initialise pole to nullptr by default. This is so you can delete[] pole in a destructor when an instance of your class goes out of scope. Else your code will leak memory like a colander leaks water.

An other way would be to use std::vector<int> pole; and let the C++ standard library take care of all the memory for you.

edited Sep 10, 2015 at 12:27

answered Sep 10, 2015 at 12:21

Bathsheba

235k35 gold badges376 silver badges504 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Gombat Over a year ago

It won't compile, remove the * in front of pole = new int [10];

Bathsheba Over a year ago

Ha ha. We'll publish jointly!

Gombat · Accepted Answer · 2015-09-10 12:23:08Z

1

The problem is, that you shadow pole's name in the scope of the function by redeclaring it. leave the int * in front of pole behind, in generate_pole, and it should work.

An example for shadowing:

int i = 0; // i is 0
std::cout << "before scope: " << i << std::endl; // prints 0
{ 
    int i = 1; 
    std::cout << "inside scope: " << i << std::endl; // prints 1
}
std::cout << "behind scope: " << i << std::endl; // prints 0

edited Sep 10, 2015 at 12:23

answered Sep 10, 2015 at 12:21

Gombat

2,08418 silver badges21 bronze badges

Collectives™ on Stack Overflow

c++ how to access variable from member function?

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related