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Home > Forums > Programmers > Languages > C++: UNIX Forum

Returning local shared_ptr ok?

Read More Threads Like This One

titanandrews (Programmer)

1 Oct 09 11:37

Hi All,

A function that returns a local object is considered undefined. But why does it seem that returning a shared_ptr is ok? Even the boost examples have this:
shared_ptr<X> createX()
{
shared_ptr<X> px(new X_impl);
return px;
}

I have never run into a case where this does not work, but I just don't know why. Does anyone have an explanation?

many thanks!

uolj (Programmer)

5 Oct 09 17:25

Returning a local object is perfectly acceptable. The problem is when you return a reference to a local object, either by returning a reference or a pointer.

In this case, you are not doing either, so you are fine. The shared_ptr object is an object, not a pointer. You are returning a copy of the shared_ptr object. A copy of the local px instance is made and then it is destroyed. It is as if you did this:

CODE

int returnTwo()
{
int i = 2;
return i;
}

If you had a pointer to the shared_ptr object, or if you returned a reference, then you'd have problems.

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