Return auto_ptr payload by value in C++ from function

Question

Does C++ standard guarantee that here would be no crash when returning auto_ptr's payload by value from the function:

class Foo { ... };

std::auto_ptr<Foo> createFoo() { 
  return std::auto_ptr<Foo>(new Foo(...));
}
...
Foo getFoo() {
  std::auto_ptr<Foo> foo(createFoo());
  return *foo; /// would be here a crash?
}

/// main
const Foo& foo(getFoo());

What's going here accordingly to the standard: *foo is copied, then foo is destroyed and finally return is performed? Or there is an another order of steps?

I tested this example with GCC and there is no crash but I am not sure that it would work with another compilers.

This is fine, but auto_ptr is deprecated, so you should avoid it. — Vaughn Cato, Feb 19 '12 at 06:44
@n.m: I didn't get you, could you please expand your question more detailed? — barankin, Feb 19 '12 at 06:46
@VaughnCato: yes, I know about its deprecated state, but I have a legacy code. — barankin, Feb 19 '12 at 06:47
I mean that if e.g. the return statement first destroyed the result and then tried to copy it, then it would be a bit hard to write working programs, wouldn't it? — n. m. could be an AI, Feb 19 '12 at 06:51
This should answer your question: http://stackoverflow.com/questions/275214/scope-and-return-values-in-c — Vaughn Cato, Feb 19 '12 at 06:51

score 2 · Answer 1 · answered Feb 19 '12 at 11:45

2

As getFoo returns by value, it creates (yet another) copy of the Foo object. After that, it doesn't matter that the original object is deleted by the auto_ptr.

Rather strange code though, to use an auto_ptr and then create a copy anyway.

answered Feb 19 '12 at 11:45

Bo Persson

90,663
31
146
203

score 1 · Accepted Answer · answered Feb 19 '12 at 11:13

1

It is very strange code, but, yes - it is guaranteed. There is no RVO, or move semantics, so it should be ok.

answered Feb 19 '12 at 11:13

innochenti

1,093
2
8
23

Return auto_ptr payload by value in C++ from function

2 Answers2