CODEWITHSUNDEEP
c++arraysfunctionmember
mrkvator
mrkvator

Reputation: 5

c++ how to access variable from member function?

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!

Upvotes: 0

Views: 71

Answers (2)

Bathsheba
Bathsheba

Reputation: 234875

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.

Upvotes: 2

Gombat
Gombat

Reputation: 2084

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

Upvotes: 1

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