On Tue, Nov 24, 2015 at 11:26 PM Roy Stogner <royst...@ices.utexas.edu>
wrote:
> We allocate it, so someone has to free it. We don't know how long an
> app is going to use it, so the library can't free it, so the app has
> to free it. UniquePtr and AutoPtr make that the default behavior, and
> so prevent accidental memory leaks.
>
Sure - I understand the reason why it's not a raw pointer. My question was
why it's a UniquePtr instead of an AutoPtr (or better yet a shared_ptr....
which you answered down below).
> > Finally, would it be ok to change it to AutoPtr
>
> We deprecated AutoPtr; when C++11 is enabled it's a UniquePtr under
> the hood now.
>
> This is nice in some ways (you can just toss them in containers if you
> know you're using C++11) and debatable in others (you can't hand off
> ownership trivially or accidentally).
>
Actually - this is the problem. This isn't really true. If you put a
UniquePtr in a container... and then you get it out of the container by
copy (like you would for a normal pointer)... it _removes_ it from the
container (leaves a NULL pointer behind in the UniquePtr in the
container). That _sucks_.
I hit that just yesterday and got a nice segfault from it (first time
through the loop everything worked swimmingly... second time through got a
segfault because it picked up a NULL pointer out of the vector these things
were stored in).
> > (or a shared_ptr, do we use those in libMesh yet?).
>
> We test for them and define LIBMESH_HAVE_CXX11_SHARED_PTR but since
> they're not in C++03 we don't use them in library code. I love
> shared_ptr but I'm too lazy to strip out the Boost version to give us
> a fallback.
>
The time for deprecating _C++03_ support is coming soon. Shared pointers
are awesome. Even I, who normally hates this kind of stuff, now ONLY use
std::shared_ptr in all of my own code. No more raw pointers anywhere.
(Not that raw pointers are evil, but that shared_ptrs are _awesome_).
Anyway - thanks for the discussion guys... I think I get it. I'll continue
to just call release() on every Auto/UniquePtr I get from libMesh (like I
always have). The only difference is I'll now wrap that release() in a
nice std::shared_ptr ;-)
Derek
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