Is returning auto_ptr from functions wrong/error-prone?

Question

Let's say I'm using std::auto_ptr in my code.*

Is there any danger in returning an std::auto_ptr object?
i.e. Could it result in a memory leak, undefined behavior, etc.? or is it a safe use of std::auto_ptr?

^{*I'm not asking if there is a better substitute (like shared_ptr); I'm specifically asking about the pitfalls of returning auto_ptr itself.}

It's not wrong and it's not error-prone. `auto_ptr` works perfectly for that case. — Jonathan Wakely, Jul 01 '13 at 08:31
@JonathanWakely: Cool, thanks, just wanted to make sure I'm not missing anything (a direct answer didn't come up in searches). — user541686, Jul 01 '13 at 08:36
Although you're right about this functionality of auto_ptr, bear in mind that it is deprecated in C++11 and `unique_ptr` is preferred instead. — the_mandrill, Jul 01 '13 at 08:38
@the_mandrill: Yup I'm aware, it's still useful though. Namely when trying to stay backwards-compatible, as well as when the result might be used in `boost::ptr_vector::push_back` or whatever. — user541686, Jul 01 '13 at 08:41
This is exactly what `auto_ptr` was designed for. The original proposal was for something more like `scoped_ptr`, and some one (I think it was Bill Gibbons) pointed out that they'd found the transfer of ownership semantics very useful for things like factory methods. The result was `auto_ptr`. — James Kanze, Jul 01 '13 at 08:48

score 4 · Accepted Answer · edited Jul 01 '13 at 12:47

In general it's safe and can lead to more robust code. It should not lead to a memory leak since the memory pointed to is automatic deleted.

But there are some cases where you have to take care:

Copies of auto_ptr are not equal!
Construction of one auto_ptr from another will release the object the first pointer was pointing to

Please see here:

The auto_ptr template class is designed to help manage memory in a semi-automatic way and prevent memory leaks when unexpected events such as exceptions would otherwise have caused the normal cleanup code to be skipped.

(quoted from (2))

Is returning auto_ptr from functions wrong/error-prone?

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