Why local class object is not deleted after it is returned in C++?

Asked Jul 27 '17 at 19:18

Active Jul 27 '17 at 19:21

Viewed 68 times

I was just looking into C++ OOP basics and actually surprised after trying this:

class A {
public:
    A() :i(10), j(20) { cout << "constructor " << endl; }
    A(const A &obj)
    {
        cout << "copy constructor" << endl;
    }
    int i;
    int j;
    ~A() { cout << "destructor " << endl; }
};

A func()
{
    A loc;
    cout<<&loc<<endl;
    return loc;
}

int main()
{
    A obj = func();
    cout<<&obj<<endl;
}

I ran the above code using g++ (GCC) 4.8.5

The output is:

constructor 10
0x71a5b3354010
0x71a5b3354010
destructor 10

Here, First,I was expecting copy constructor to be called. But it didn't (when ran with MSVC++ 14.0 it did). And how could be the local object in main() be the same as the object in func() (it gave the same object address)?

I'm just a beginner in C++ and couldn't understand that behaviour. Please clarify!!!

edited Jul 27 '17 at 19:21

asked Jul 27 '17 at 19:18

infinite loop

1,309
9
19

2

Is `A obj = display();` meant to be `A obj = func();`? – Xirema Jul 27 '17 at 19:20
1

You never seem to call func(), so I don't see how you could have obtained the address of a local variable in it. – Jul 27 '17 at 19:21
@juanchopanza you beat me to closing this by about 2 seconds ;) – NathanOliver Jul 27 '17 at 19:21
@Xirema, Corrected the question. – infinite loop Jul 27 '17 at 19:22
@NeilButterworth, You mean to say, the new object has been created in the same place as deleted object? – infinite loop Jul 27 '17 at 19:25
1

@infinite The compiler is optimising the use of space on the stack. – Jul 27 '17 at 19:25
2

@infinite No object has been deleted - note that `delete` has a special meaning in C++. – Jul 27 '17 at 19:25
@NeilButterworth, yeah sorry for that term!!! – infinite loop Jul 27 '17 at 19:27
2

@NeilButterworth, not really. Nobody cares about the use of the space on the stack. Compiler is optimizing number of constructors being called. – SergeyA Jul 27 '17 at 19:30
1

@SergeyA, exactly. If its about space reusing, atleast there'll be an extra constructor and destructor in prints – infinite loop Jul 27 '17 at 19:31

Why local class object is not deleted after it is returned in C++?

0 Answers0