[Boost-users] minor boost::interprocess::vector bug (?)

Subject: [Boost-users] minor boost::interprocess::vector bug (?)
From: Bob Walters (bob.s.walters_at_[hidden])
Date: 2009-08-13 17:08:19

I have encountered a minor bug with boost::interprocess::vector<>
which involves a situation where std::uninitialized_copy() is invoked
with a NULL pointer value, and length of 0.  I’m not sure if that is
truly an error, but unfortunately the MWVC (9.0) debug library has an
assertion which gets tripped by the null pointer value, so I've had
little choice but to patch my copy of the code to prevent that call
from happening.  Let me know if you want me to create a trac item for
this problem.

The problem occurs when an empty vector (created by the single
allocator argument constructor) is swapped with a vector that has an
established capacity.  Specifically, I see this with the following
code:

        boost::interprocess::vector<char,char_alloc_type> *buffer =
somewhere_in_shared_memory;
        // can’t construct ovectorstream to use buffer directly, but can swap
it into place:
        boost::interprocess::basic_ovectorstream< buffer_t<void_alloc_t> >
vstream(buffer->get_allocator());
        vstream.swap_vector(*buffer);

On msvc (9.0), somewhere below priv_range_insert(), a call gets issued
to std::uninitialized_copy with a null pointer and length of 0.  My
solution to this was to modify vector::swap as follows:

diff -r ./containers/container/vector.hpp
../../../../boost_1_39_0/boost/interprocess/containers/container/vector.hpp
1206,1208c1206,1210
<          this->reserve(new_size);
<          containers_detail::default_construct_aux_proxy<T, T*,
size_type> proxy(n);
<          priv_range_insert(this->cend().get_ptr(), n, proxy);
---
>                if (n>0) {
>                       this->reserve(new_size);
>                        containers_detail::default_construct_aux_proxy<T, T*, size_type> proxy(n);
>                        priv_range_insert(this->cend().get_ptr(), n, proxy);
>                }
Again, let me know if you want me to create a ticket for this problem.