What happens when constructor's parameter has same name as member variable?

Question

I am trying a code which goes like this:-

class Something
{
private:
    int data;

public:
    Something(int data)
    {
       data = data;
    }
    int getdata()
    {
        return data;
    }
};


int main()
{
    Something xyz(5);
    cout<<xyz.getdata()<<endl;
    return 0;
}

The output of this is "0". i am stuck why this is coming as 0. kindly help. TIA.

replaced the line data=data by this->data = data and it works fine. — Lalu Parshad, Jan 23 '16 at 04:46
i mean to ask why 0 is coming. since = operator has right to left associativity then data must be resolve first and the new data should be 5. — Lalu Parshad, Jan 23 '16 at 04:47
it should be like this:- Something(int data) { data = 5; } But when you print the data it gives 0. — Lalu Parshad, Jan 23 '16 at 04:57
Use the member initializer list: `Something(int data) : data(data) {}` The compiler sorts out which is which. — Jerry Coffin, Jan 23 '16 at 04:59
@LaluParshad: give more tries without fix with different compiler and OS. And I am sure that you will see some garbage value instead of 0. — rahul.deshmukhpatil, Jan 23 '16 at 05:14
@rahul.deshmukhpatil even the random value doesn't explain the behaviour. Something(5){ data = 5 ; } — Lalu Parshad, Jan 23 '16 at 05:24
@LaluParshad Associativity has nothing to do with it. It is purely and simply a scoping problem. The parameter hides the member variable. — user207421, Jan 23 '16 at 07:21
Possible duplicate of [Name hiding in constructor initialization list](http://stackoverflow.com/questions/14716337/name-hiding-in-constructor-initialization-list) — Jaege, Jan 23 '16 at 10:28

score 3 · Answer 1 · answered Jan 23 '16 at 06:06

You can change the definition to

Something(int data):data(data)
{
}

and it will work, too. The parameter data hides the field data in the scope of the function. this->data explicitly specifies the scope to be that of the class. I can't tell you why the above declaration works other than to say that the elements in the initialization list of the constructor must be fields of the class instance. So this may imply the scope. While the values with which they are initialized come from the function scope.

What happens when constructor's parameter has same name as member variable?

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