Thread: assignment to auto_ptr

Hi,
I am learning to use auto_ptr.
my question is in purple comments below.

Code:

#include <iostream>
using namespace std;

class Base
{
public:
    virtual void print()=0;
};

class A : public Base
{
public:
    void print() { cout << "A" << endl; }
};

class B : public Base
{
public:
    void print() { cout << "B" << endl; }
};

int main()
{
    auto_ptr<Base> owner;
    
    if(5==5)
    {
        A* a = new A;
        owner = a;    // this was my first guess, does not compile though.
        owner = auto_ptr<Base>(a); // this compiles. is this how you do it?
    }
    else
    {
        B* b = new B;
        owner = auto_ptr<Base>(b);
    }

    owner->print();

    return 0;
}

Thanks laserlight.

Originally Posted by CornedBee

You should do

Code:

owner.reset(new A);

Why? isn't it the same?

Originally Posted by kroiz

Why? isn't it the same?

not exactly

Code:

owner = auto_ptr<Base>(new A);

creates an unnecessary temporary auto_ptr that is then assigned to owner.
Kurt

Understood.
Thanks you all.

Is it the same with boost::shared_ptr regarding .reset() thing?

Yes. reset() allows smart pointers to take ownership of an object by swapping it into its this pointer. That's all reset does, and you should use it.