Re: Help: auto_ptr conversion confusion

[Benjamin Kosnik <bkoz at redhat dot com>]

> I am unsure if it is an error in the implemetation of auto_ptr or if
> it is an error in the G++ frontend, or just an incorrect library
> documentation.
> 
> The aparent problem is that the following selfcontained program
> does not compile with GCC3.2:
> 
>  1 #include <memory>
>  2 using namespace std;
>  3
>  4 struct A {};
>  5 struct B: A {};
>  6
>  7 auto_ptr<B> f()
>  8 {
>  9   auto_ptr<B> b;
> 10   return b;
> 11 }
> 12
> 13 int main()
> 14 {
> 15   auto_ptr<A> a = f();
> 16   return 0;
> 17 }

I think this usage is in error.

> But in your source level documentation you state that the
> alternative construct using = should work:
> http://gcc.gnu.org/onlinedocs/libstdc++/libstdc++-html-USERS-3.2/classstd_1_
> 1auto__ptr.html#z15_3
> 
> 
> Could someone explain to me exactly what the semantical difference (if
> any) is between these two versions of line 15:
> 
> 15   auto_ptr<A> a = f();
> 15   auto_ptr<A> a(f());
> 
> Does gcc3.2 handle these alternative constructs the way it is intended
> ib the C++ standard?

I think this documentation should be corrected.

I'm uncertain about this, and have cc'd Jack Reeves, who seems to have
done the latest work on std::auto_ptr. Perhaps he'll be able to explain
in more detail.

-benjamin