Note: I'm using boost 1.33.1 here Sebastian Redl wrote:

This code should really not give you any warnings. (And doesn't on GCC, though I doubt that'll help you.) C4244, so that others don't have to look it up, is the "conversion with possible data loss" warning. This indicates that in VC++, make_counting_iterator returns a counting_iterator<long> or even <__int64>. Can somebody with that compiler post the output of this line? std::cout << typeid(boost::make_counting_iterator(1)).name() << std::endl;

A simple workaround for this particular warning ought to be to

Using Visual Studio .NET 2003, the output of this was: class boost::counting_iterator as it should be. directly instantiate counting_iterators with their template parameter set correctly.

Sebastian Redl

The problem appears to be when operator += is called on the iterator. Here, the difference_type of the iterator, boost::iterator_facade::difference_type, which is equal to boost::detail::counting_iterator_base::difference, is __int64. The counting_iterator_base uses the following typedef: typedef typename detail::ia_dflt_help< Difference , mpl::eval_if< is_numeric<Incrementable> , numeric_difference<Incrementable> , iterator_difference<Incrementable> > >::type difference; It seems this has been discovered before: http://lists.boost.org/Archives/boost/2004/07/69347.php The actual warnings I received compiling this code were: -------------------------------------------------------- Compiling... BoostTest1.cpp d:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\xutility(481) : warning C4244: '+=' : conversion from 'boost::iterators::enabled<__formal>::base<T>::type' to 'std::vector<_Ty>::size_type', possible loss of data with [ __formal=true, T=std::iterator_traits>::difference_type ] and [ _Ty=int ] d:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\xutility(498) : see reference to function template instantiation 'void std::_Distance2<_InIt,_Diff>(_RanIt,_RanIt,_Diff &,std::random_access_iterator_tag)' being compiled with [ _InIt=boost::counting_iterator, _Diff=std::vector<int>::size_type, _RanIt=boost::counting_iterator ] d:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\vector(657) : see reference to function template instantiation 'void std::_Distance<_Iter,std::vector<_Ty>::size_type>(_InIt,_InIt,_Diff &)' being compiled with [ _Iter=boost::counting_iterator, _Ty=int, _InIt=boost::counting_iterator, _Diff=std::vector<int>::size_type ] d:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\vector(634) : see reference to function template instantiation 'void std::vector<_Ty>::_Insert<_Iter>(std::vector<_Ty>::iterator,_Iter,_Iter,std::forward_iterator_tag)' being compiled with [ _Ty=int, _Iter=boost::counting_iterator ] d:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\vector(366) : see reference to function template instantiation 'void std::vector<_Ty>::insert<_Iter>(std::vector<_Ty>::iterator,_Iter,_Iter)' being compiled with [ _Ty=int, _Iter=boost::counting_iterator ] d:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\vector(343) : see reference to function template instantiation 'void std::vector<_Ty>::_Construct<_Iter>(_Iter,_Iter,std::input_iterator_tag)' being compiled with [ _Ty=int, _Iter=boost::counting_iterator ] g:\Projects\BoostTest1\BoostTest1.cpp(15) : see reference to function template instantiation 'std::vector<_Ty>::vector>(_Iter,_Iter)' being compiled with [ _Ty=int, Incrementable=int, CategoryOrTraversal=boost::use_default, Difference=boost::use_default, _Iter =boost::counting_iterator ] d:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\boost\iterator\iterator_adaptor.hpp(329) : warning C4244: '+=' : conversion from 'boost::iterator_facade::difference_type' to 'int', possible loss of data with [ Derived=boost::counting_iterator, Value=const boost::mpl::identity<const int>::type, CategoryOrTraversal=boost::mpl::identityboost::random_access_traversal_tag::type, Reference=boost::mpl::identity::type, Difference=boost::mpl::identity::difference>::type ] d:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\boost\iterator\iterator_adaptor.hpp(327) : while compiling class-template member function 'void boost::iterator_adaptor::advance(boost::iterator_facade::difference_type)' with [ Derived=boost::counting_iterator, Base=int, Value=const int, Traversal=boost::detail::counting_iterator_base::traversal, Reference=const int &, Difference=boost::detail::counting_iterator_base::difference, CategoryOrTraversal=boost::mpl::identityboost::random_access_traversal_tag::type ] d:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\boost\iterator\counting_iterator.hpp(153) : see reference to class template instantiation 'boost::iterator_adaptor' being compiled with [ Derived=boost::counting_iterator, Base=int, Val ue=const int, Traversal=boost::detail::counting_iterator_base::traversal, Reference=const int &, Difference=boost::detail::counting_iterator_base::difference ] g:\Projects\BoostTest1\BoostTest1.cpp(12) : see reference to class template instantiation 'boost::counting_iterator' being compiled with [ Incrementable=int, CategoryOrTraversal=boost::use_default, Difference=boost::use_default ]

Sebastian Redl writes:

Whatever. Different workaround is to modify boost/iterator/iterator_adaptor.hpp:

+ #if defined(BOOST_MSVC) + #pragma warning(disable: 4244) + #endif void advance(typename super_t::difference_type n) {

BOOST_ITERATOR_ADAPTOR_ASSERT_TRAVERSAL(random_access_traversal_tag) m_iterator += n; } + #if defined(BOOST_MSVC) + #pragma warning(default: 4244) + #endif

This is potentially unsafe, of course - nothing prevents you from just passing a HUGE value to +=. The likelyhood, though ... well, it's just a workaround.

No static checking (e.g. warning) can protect you from the possibility of runtime overflows in integer operations. The overflow can occur with or without the warning disabled. These "integer size warnings" are nothing more than a nuisance in most generic code. IMO they should be turned off on the command line. Turning them off in individual source files leaves them cluttered with workarounds and #ifdefs. -- Dave Abrahams Boost Consulting www.boost-consulting.com