Question

The following example compiles fine when using GCC 4.4.6 with the –std=c++0x flag but fails to compile in C++03 mode.

#include <stdint.h>
#include <boost/container/vector.hpp>

struct data
{
   int               i_;
   boost::container::vector<data>      v_;
};

int main( int argc, char** argv )
{
    data myData;
    myData.i_ = 10;

    data myData2;
    myData2.i_ = 30;

    myData.v_.push_back( myData2 );

    return 0;
}

It compiles successfully with

 g++ --std=c++0x test-cont.cpp

However if I remove the --std=c++0x I get the following errors:
g++ test-cont.cpp
In file included from
include/c++/4.4.6/memory:49,
boost/container/container_fwd.hpp:36,
boost/container/vector.hpp:20,
from test-cont.cpp:2:

include/c++/4.4.6/bits/stl_algobase.h: In static member function 
    static _OI std::__copy_move<false, false, std::random_access_iterator_tag>::
        __copy_m(_II, _II, _OI) [with _II = 
            boost::container::constant_iterator<data, long int>, _OI = data*]:

include/c++/4.4.6/bits/stl_algobase.h:397:   instantiated from 
    _OI std::__copy_move_a(_II, _II, _OI) 
        [with bool _IsMove = false, 
                   _II = boost::container::constant_iterator<data, long int>, _OI = data*]

include/c++/4.4.6/bits/stl_algobase.h:436:   instantiated from 
    _OI std::__copy_move_a2(_II, _II, _OI) 
    [with bool _IsMove = false, 
               _II = boost::container::constant_iterator<data, long int>, _OI = data*]

include/c++/4.4.6/bits/stl_algobase.h:468:   instantiated from 
    _OI std::copy(_II, _II, _OI) 
        [with _II = boost::container::constant_iterator<data, long int>, _OI = data*]

boost/move/move.hpp:1147:   instantiated from 
    boost::copy_or_move(I, I, F, 
        typename boost::move_detail::disable_if< boost::move_detail::is_move_iterator<I>, void>::type*) 
        [with I = boost::container::constant_iterator<data, long int>, F = data*]

boost/container/detail/advanced_insert_int.hpp:58:   instantiated from 
    void boost::container::container_detail::advanced_insert_aux_proxy<A, FwdIt, Iterator>::copy_remaining_to(Iterator) 
    [with A = std::allocator<data>, FwdIt = boost::container::constant_iterator<data, long int>, Iterator = data*]

test-cont.cpp:21:   instantiated from here

include/c++/4.4.6/bits/stl_algobase.h:343: error: 
    no match for operator= in * __result = 
        __first.boost::container::constant_iterator<T, Difference>::operator* 
        [with T = data, Difference = long int]()

test-cont.cpp:5: note: candidates are: data& data::operator=(data&)

It looks like boost::container::vector requires move semantics which I assumed would automatically use boost::move when compiled with a c++03 compiler.

If I manually modify the struct data to define:

1. a default constructor
2. a copy constructor
3. an assignment operator
4. an emulated move constructor using BOOST_RV_REF
5. an emulated move assignment operator using BOOST_RV_REF

The example compiles.

Having to manually add these move/copy constructors and assignment operators for C++03 is laborious.

Is this a bug with boost::container? If so what is the best way to report it to the boost community.

Answer 1

This is a limitation to the emulation in C++03 (from here):

The macro BOOST_COPYABLE_AND_MOVABLE needs to define a copy
constructor for copyable_and_movable taking a non-const parameter in
C++03 compilers:

//Generated by BOOST_COPYABLE_AND_MOVABLE
copyable_and_movable &operator=(copyable_and_movable&){/**/}

Since the non-const overload of the copy constructor is generated,
compiler-generated assignment operators for classes containing
copyable_and_movable will get the non-const copy constructor overload,
which will surely surprise users.
This limitation forces the user to define a const version of the copy
assignment, in all classes holding copyable and movable classes which
might annoying in some cases.

In your case boost::container::vector<data> v_; uses BOOST_COPYABLE_AND_MOVABLE(vector) hence the error.