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dijkstra_shortest_paths and Python
by Hugo Ferreira 30 Nov '06

30 Nov '06

HI there, I'm trying to use the BGL bindings for python found here: http://www.osl.iu.edu/~dgregor/bgl-python/ The problem is that I can't seem to understand how the dijkstra_shortest_paths() and the corresponding graph works. My code, so far, is like this: ---8<---8<--- import boost as bgl graph = bgl.Graph() a = graph.add_vertex() b = graph.add_vertex() e = graph.add_edge(a, b) weights = graph.edge_property_map('integer') weights[e] = 5 graph.edge_properties['weight'] = weights boost.dijkstra_shortest_paths(graph, a) ---8<---8<--- Which, of course, complains about the dijkstra_shortest_paths function signature. Can anyone please provide me an working example of setting up a graph and calling this function? I basically need the shortest path from vertex A to vertex B. Thanks in advance, Hugo Ferreira -- GPG Fingerprint: B0D7 1249 447D F5BB 22C5 5B9B 078C 2615 504B 7B85

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BGL: Retrieving a vertex_descriptor from a custom property?
by Peter Palotas 30 Nov '06

30 Nov '06

I'm wondering if it is somehow possible to attach a custom property (eg. a pointer to some object) to each vertex in a graph, and then lookup the vertex based on that index? My first attempt was to use a simple map outside of the graph, mapping my custom property to a vertex_descriptor, but since the vertex_descriptors seem to change as vertices are inserted and removed this does not work. Is it possible to do this using BGL? An example would be greatly appreciated. Sincerely, Peter

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more lambda issues
by Noah Roberts 30 Nov '06

30 Nov '06

I'm kind of loosing faith that this list ever responds to questions but here goes anyway. I've narrowed a problem down to this: #include <iostream> #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> struct test_b { test_b() { std::cerr << "test_b::test_b()\n"; } test_b(test_b const&) { std::cerr << "test_b::test_b(test_b const&)\n"; } virtual int f() = 0; //{ return 5; } }; struct test_d : test_b { test_d() : test_b() { std::cerr << "test_d::test_d()\n"; } test_d(test_d const& d) : test_b(d) { std::cerr << "test_d::test_d(test_d const&)\n"; } int f() { return 5; } }; int main(void) { namespace l = boost::lambda; test_b & td = test_d(); std::cerr << "Value: " << (l::bind(&test_b::f, l::_1))(td) << "\n"; int x; std::cin >> x; } Compiler result: cannot instantiate abstract class test_b. Because lambda doesn't seem to be able to handle smart pointers at all I have been trying to come up with a way to pass the dereferenced result into the function call. Nothing is working. In the end lambda must be able to handle the above in order to make this work. If lambda cannot handle this simple case I just don't see how it can be any use. The full compiler output follows: 1>c:\boost\include\boost-1_33_1\boost\tuple\detail\tuple_basic.hpp(419) : error C2259: 'test_b' : cannot instantiate abstract class 1> due to following members: 1> 'int test_b::f(void)' : is abstract 1> c:\documents and settings\nroberts\my documents\visual studio 2005\projects\playground\playground\playground.cpp(14) : see declaration of 'test_b::f' 1> c:\boost\include\boost-1_33_1\boost\tuple\detail\tuple_basic.hpp(329) : see reference to class template instantiation 'boost::tuples::cons<HT,TT>' being compiled 1> with 1> [ 1> HT=test_b, 1> TT=boost::lambda::detail::deduce_non_ref_argument_types_<boost::tuples::cons<const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,boost::tuples::detail::map_tuple_to_cons<boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>::type>::tail_type,boost::tuples::tuple<test_b &,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>::type 1> ] 1> c:\boost\include\boost-1_33_1\boost\lambda\detail\lambda_functor_base.hpp(151) : see reference to class template instantiation 'boost::tuples::cons<HT,TT>' being compiled 1> with 1> [ 1> HT=int (__thiscall test_b::* const )(void), 1> TT=boost::tuples::cons<test_b,boost::lambda::detail::deduce_non_ref_argument_types_<boost::tuples::cons<const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,boost::tuples::detail::map_tuple_to_cons<boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>::type>::tail_type,boost::tuples::tuple<test_b &,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>::type> 1> ] 1> c:\boost\include\boost-1_33_1\boost\lambda\detail\lambda_functor_base.hpp(228) : see reference to class template instantiation 'boost::lambda::detail::has_null_type<Tuple>' being compiled 1> with 1> [ 1> Tuple=boost::tuples::cons<int (__thiscall test_b::* const )(void),boost::tuples::cons<test_b,boost::lambda::detail::deduce_non_ref_argument_types_<boost::tuples::cons<const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,boost::tuples::detail::map_tuple_to_cons<boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>::type>::tail_type,boost::tuples::tuple<test_b &,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>::type>> 1> ] 1> c:\boost\include\boost-1_33_1\boost\lambda\detail\lambda_functor_base.hpp(398) : see reference to class template instantiation 'boost::lambda::detail::deduce_non_ref_argument_types<Args,SigArgs>' being compiled 1> with 1> [ 1> Args=boost::tuples::tuple<int (__thiscall test_b::* const )(void),const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type>, 1> SigArgs=boost::tuples::tuple<test_b &,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type> 1> ] 1> c:\documents and settings\nroberts\my documents\visual studio 2005\projects\playground\playground\playground.cpp(32) : see reference to class template instantiation 'boost::lambda::lambda_functor_base<Act,Args>::sig<SigArgs>' being compiled 1> with 1> [ 1> Act=boost::lambda::action<2,boost::lambda::function_action<2>>, 1> Args=boost::tuples::tuple<int (__thiscall test_b::* const )(void),const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type>, 1> SigArgs=boost::tuples::tuple<test_b &,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type> 1> ]

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Re: [Boost-users] Suggestion for boost`s smart pointers
by Sohail Somani 30 Nov '06

30 Nov '06

> -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org] On Behalf Of mark cox > Sent: Tuesday, November 28, 2006 2:37 PM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] Suggestion for boost`s smart pointers > > wow, this seems like a great idea, a scoped_ptr with deleter > would be v.useful. > mark I've been thinking something like (just something I hacked together just now). Not sure if there is a nicer way. #include <string> #include <cstdio> #include <iostream> template<typename T> struct DeletingDeleter { DeletingDeleter(T * p) { delete p; std::cout << "DeletingDeleter" << std::endl; } }; struct FileCloser { FileCloser(FILE * f) { std::cout << "Closing file" << std::endl; fclose(f); } }; template<typename T, typename Deleter=DeletingDeleter<T> > struct scoped_ptr { scoped_ptr():p_(0){} scoped_ptr(T * p):p_(p){} ~scoped_ptr() { Deleter d(p_); } T * get() {return p_;} // regular stuff private: T * p_; }; typedef scoped_ptr<FILE,FileCloser> file_ptr; int main() { scoped_ptr<int> a; // maintain old interface scoped_ptr<int> b(new int(5)); file_ptr p(fopen("myfile.txt","w")); fprintf(p.get(),"Hello world!\n"); }

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Re: [Boost-users] [Serialization] error C2027: use of undefined type 'boost::serialization::extended_type_info_null<T>'?
by Lawrence Spector 30 Nov '06

30 Nov '06

Ok, I got past the errors I was having last night. Seemed to have to do with the ordering of the libraries and then an incorrect constant used in the load method. Moving on, I now get the following linker errors: Linking... Creating library Debug/SerializationDemo.lib and object Debug/SerializationDemo.exp demo.obj : error LNK2019: unresolved external symbol "public: __thiscall boost::archive::basic_text_oprimitive<class std::basic_ostream<unsigned short,struct std::char_traits<unsigned short> > >::~basic_text_oprimitive<class std::basic_ostream<unsigned short,struct std::char_traits<unsigned short> > >(void)" (??1?$basic_text_oprimitive@V?$basic_ostream@GU?$char_traits@G@std@@@std @@@archive@boost@@QAE@XZ) referenced in function "public: __thiscall boost::archive::text_woarchive_impl<class boost::archive::text_woarchive>::~text_woarchive_impl<class boost::archive::text_woarchive>(void)" (??1?$text_woarchive_impl@Vtext_woarchive@archive@boost@@@archive@boost@ @QAE@XZ) demo.obj : error LNK2019: unresolved external symbol "public: __thiscall boost::archive::text_wiarchive_impl<class boost::archive::text_wiarchive>::text_wiarchive_impl<class boost::archive::text_wiarchive>(class std::basic_istream<unsigned short,struct std::char_traits<unsigned short> > &,unsigned int)" (??0?$text_wiarchive_impl@Vtext_wiarchive@archive@boost@@@archive@boost@ @QAE@AAV?$basic_istream@GU?$char_traits@G@std@@@std@@I@Z) referenced in function "public: __thiscall boost::archive::text_wiarchive::text_wiarchive(class std::basic_istream<unsigned short,struct std::char_traits<unsigned short> > &,unsigned int)" (??0text_wiarchive@archive@boost@@QAE@AAV?$basic_istream@GU?$char_traits @G@std@@@std@@I@Z) demo.obj : error LNK2019: unresolved external symbol "public: __thiscall boost::archive::basic_text_iprimitive<class std::basic_istream<unsigned short,struct std::char_traits<unsigned short> > >::~basic_text_iprimitive<class std::basic_istream<unsigned short,struct std::char_traits<unsigned short> > >(void)" (??1?$basic_text_iprimitive@V?$basic_istream@GU?$char_traits@G@std@@@std @@@archive@boost@@QAE@XZ) referenced in function "public: __thiscall boost::archive::text_wiarchive_impl<class boost::archive::text_wiarchive>::~text_wiarchive_impl<class boost::archive::text_wiarchive>(void)" (??1?$text_wiarchive_impl@Vtext_wiarchive@archive@boost@@@archive@boost@ @QAE@XZ) demo.obj : error LNK2019: unresolved external symbol "public: __thiscall boost::archive::basic_text_oprimitive<class std::basic_ostream<unsigned short,struct std::char_traits<unsigned short> > >::basic_text_oprimitive<class std::basic_ostream<unsigned short,struct std::char_traits<unsigned short> > >(class std::basic_ostream<unsigned short,struct std::char_traits<unsigned short> > &,bool)" (??0?$basic_text_oprimitive@V?$basic_ostream@GU?$char_traits@G@std@@@std @@@archive@boost@@QAE@AAV?$basic_ostream@GU?$char_traits@G@std@@@std@@_N @Z) referenced in function "public: __thiscall boost::archive::text_woarchive_impl<class boost::archive::text_woarchive>::text_woarchive_impl<class boost::archive::text_woarchive>(class std::basic_ostream<unsigned short,struct std::char_traits<unsigned short> > &,unsigned int)" (??0?$text_woarchive_impl@Vtext_woarchive@archive@boost@@@archive@boost@ @QAE@AAV?$basic_ostream@GU?$char_traits@G@std@@@std@@I@Z) Debug/SerializationDemo.exe : fatal error LNK1120: 4 unresolved externals However, if I change the build type to not be unicode, then it all compiles, links, and works. I checked to see what libraries are being linked in a non- unicode build vs. a unicode: Non-Unicode: Linking to lib file: libboost_serialization-vc71-sgd-1_33_1.lib // Good Linking to lib file: libboost_serialization-vc71-sgd-1_33_1.lib // Good Unicode: Linking to lib file: libboost_wserialization-vc71-sgd-1_33_1.lib // Good Linking to lib file: libboost_serialization-vc71-sgd-1_33_1.lib // Why?? Linking to lib file: libboost_serialization-vc71-sgd-1_33_1.lib // Why?? Any ideas? Does the boost serialization possibly have unicode issues in 1.33.1? Thanks in advance, Lawrence

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Re: [Boost-users] serialize explicit template instantiation
by Reusser, Edward 30 Nov '06

30 Nov '06

This email was an eye popper for me because I have never had any luck declaring a template function in a header file and defining the implementation in a cpp file. I either get compilation/link errors, or very odd run-time problems. My understanding is that many compilers (of which mine, the MSVC 7.1 compiler) simply cannot handle this situation at all. I have always had to include the actual implementation of the template function inside the header file, which is a real pain. Note that this has nothing to do with the serialization per se. Are other people finding that newer compilers are finally able to handle this? I have several projects that I could improve by splitting the implementation code away from the headers. Ed -----Original Message----- From: Robert Ramey [mailto:ramey@rrsd.com] Sent: Wednesday, November 29, 2006 8:33 AM To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] serialize explicit template instantiation I just compiled, linked and ran the following program on my system: vc 7.1 Boost 1.35 - HEAD There was no need to explicitly instantiate anything. Robert Ramey #include <boost/serialization/string.hpp> #include <boost/serialization/base_object.hpp> #include <boost/serialization/utility.hpp> #include <boost/serialization/version.hpp> class CSerTest { std::string a_, b_, c_; friend class boost::serialization::access; template<class Archive> void serialize( Archive & ar, const unsigned int ); public: CSerTest(); }; BOOST_CLASS_VERSION(CSerTest, 1); // Class.cpp #include <boost/archive/xml_oarchive.hpp> #include <boost/archive/xml_iarchive.hpp> CSerTest::CSerTest() : a_("1"), b_("2"), c_("3") { } template<class Archive> void CSerTest::serialize( Archive & ar, const unsigned int ) { ar & BOOST_SERIALIZATION_NVP(a_) & BOOST_SERIALIZATION_NVP(b_) & BOOST_SERIALIZATION_NVP(c_); } // main.cpp #include <fstream> ///////////////////////// without effect //////////////////////////////////// //template void CSerTest::serialize<boost::archive::xml_oarchive>(boost::archive::xml_oa rchive&, unsigned int ); int main() { const CSerTest instance; std::ofstream ofs( "out_file.txt" ); boost::archive::xml_oarchive oxa( ofs ); oxa << BOOST_SERIALIZATION_NVP(instance); } The information contained in or attached to this email may be subject to the Export Administration Regulations (EAR), administered by the U.S. Department of Commerce, or the International Traffic in Arms Regulations (ITAR), administered by the U.S. Department of State, and may require an export license from the Commerce or State Department prior to its export. An export can include a release or disclosure to a foreign national inside or outside the United States. Include this notice with any reproduced portion of this information.

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Re: [Boost-users] more lambda issues
by Johan Torp 30 Nov '06

30 Nov '06

I haven't read all of your posts but I think your main problem is that boost bind stores arguments by value and takes them by reference. Because of this it requires lvalues as arguments. You can either add an internal bind to boost::shared_ptrs get() method which returns a raw pointer that can be bound or you can make a functor which accepts a raw pointer (given it won't outlive the shared_ptr). The latter requires you to create a temporary raw pointer when calling the functor since you need an lvalue. Consider the following: struct A{ int foo() {} }; int main() { boost::shared_ptr<A> sa; bind(&A::foo, bind(&boost::shared_ptr<A>::get,_1))(sa); A* pa=sa.get(); bind(&A::foo, _1)(pa); } Best Regards, Johan Torp boost-users-request(a)lists.boost.org wrote: >On 11/29/06, "JOAQUIN LOPEZ MU?Z" <joaquin(a)tid.es> wrote: > >First, thank you for your response. > > > >> std::cerr << "Value: " << >> (l::bind(&test_b::f, l::_1))(boost::ref(td)) << "\n"; >> >> > >Well, I tried putting ref on the other side but this works...my way didn't. > >Now I would need to find how to use this solution for my original >problem when td is actually a shared_ptr to an abstract base: > >boost::shared_ptr<test_b> td = boost::shared_ptr<test_b>(new test_d); > >This does not work: > >l::bind(l::bind(&test_b::f, l::_1), boost::ref(*l::_1))(td) > >Unlike boost::bind, lambda::bind doesn't work like this: > >l::bind(&test_b::f, l::_1)(td) > >This does but can't be used in an algorithm on a container holding >smart pointers: > >l::bind(&test_b::f, l::_1)(boost::ref(*td)) > >Interestingly, boost::bind has an operator == that will allow me to >compare the result of f() to a value just fine...I thought I needed >lambda for this. Boost::bind doesn't suffer from an inability to work >directly with smart pointers and doesn't require special magic to use >them vs. raw vs. non-ptr. So my original problem is solved by tossing >lambda out the airlock but it might be worthwhile to find a way to >accomplish a smart pointer member call with lambda for the future. > >So in the end, my problem is thus: > >std::find_if(cont.begin(), cont.end(), bind(&deref_val_type::f, _1) == 5); > >How is that accomplished with lambda if cont holds smart pointers? So >far I haven't found any way... > > > -- System Developer TouchTable AB Tel: +46 (0)31 773 68 12 johan.torp(a)touchtable.se

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Re: [Boost-users] odd msvc 7.1 compilation errors with mpl
by Küppers, Ben 30 Nov '06

30 Nov '06

craigp wrote: > For some reason, I can't get the IDE to compile BOOST_MPL_ASSERT. <snip> > anyone else seen something like this before?? all the mpl regression tests > compile fine via bjam (using msvc 7.1), so it appears ide-specific, > somehow... I am seeing the same behaviour. I also noticed that a release build seems to be immune to this problem. Also, the problem goes away as soon as the two character types are replaced by template classes and the character types are passed in later. #include <boost/type_traits/is_same.hpp> #include <boost/mpl/assert.hpp> template< class T, class U > struct my { BOOST_MPL_ASSERT( ( boost::is_same< T, U > ) ); // ok }; my<char,char> test; template< class T, class U > void f() { // ... BOOST_MPL_ASSERT( ( boost::is_same< T, U > ) ); // ok BOOST_MPL_ASSERT( ( boost::is_same< char, char > ) ); // ok }; int main() { f< char, char >(); BOOST_MPL_ASSERT( ( boost::is_same< char, char > ) ); // fail } -Ben This e-mail and any attachment is for authorised use by the intended recipient(s) only. It may contain proprietary material, confidential information and/or be subject to legal privilege. It should not be copied, disclosed to, retained or used by, any other party. If you are not an intended recipient then please promptly delete this e-mail and any attachment and all copies and inform the sender. Thank you.

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gccxml compilation error with msc
by craigp 30 Nov '06

30 Nov '06

hello - i'm using gccxml (with pygccxml to generate python wrappers and fusion extension code), and under msc (7.1 in this case) i get compilation errors. it's a trivial fix, since gccxml attempts to emulate msc, it just needs another check in a couple files (naturally you'll probably want to rename 'CDP_USING_GCCXML'). i thought i'd send a patch, since i think others may try using gccxml (esp. since pygccxml is shaping up quite nicely). there are probably other places where this may be a problem, but for now, they're the only ones i've run into. HTH, --craig cvs -z9 diff -u -- and.hpp or.hpp (in directory D:\dev\boost.cvs\boost\boost\mpl\) Index: and.hpp =================================================================== RCS file: /cvsroot/boost/boost/boost/mpl/and.hpp,v retrieving revision 1.5 diff -u -r1.5 and.hpp --- and.hpp 2 Sep 2004 15:40:41 -0000 1.5 +++ and.hpp 30 Nov 2006 09:08:40 -0000 @@ -28,7 +28,7 @@ // 'or' and 'and' macros, see http://tinyurl.com/3et69; 'defined(and)' // has to be checked in a separate condition, otherwise GCC complains // about 'and' being an alternative token -#if defined(_MSC_VER) +#if defined(_MSC_VER) && !defined(CDP_USING_GCCXML) #if defined(and) # pragma push_macro("and") # undef and @@ -39,7 +39,7 @@ # define BOOST_MPL_PREPROCESSED_HEADER and.hpp # include <boost/mpl/aux_/include_preprocessed.hpp> -#if defined(_MSC_VER) +#if defined(_MSC_VER) && !defined(CDP_USING_GCCXML) #if defined(and) # pragma pop_macro("and") #endif Index: or.hpp =================================================================== RCS file: /cvsroot/boost/boost/boost/mpl/or.hpp,v retrieving revision 1.4 diff -u -r1.4 or.hpp --- or.hpp 2 Sep 2004 15:40:42 -0000 1.4 +++ or.hpp 30 Nov 2006 09:08:46 -0000 @@ -29,7 +29,7 @@ // 'or' and 'and' macros, see http://tinyurl.com/3et69; 'defined(or)' // has to be checked in a separate condition, otherwise GCC complains // about 'or' being an alternative token -#if defined(_MSC_VER) +#if defined(_MSC_VER) && !defined(CDP_USING_GCCXML) #if defined(or) # pragma push_macro("or") # undef or @@ -40,7 +40,7 @@ # define BOOST_MPL_PREPROCESSED_HEADER or.hpp # include <boost/mpl/aux_/include_preprocessed.hpp> -#if defined(_MSC_VER) +#if defined(_MSC_VER) && !defined(CDP_USING_GCCXML) #if defined(or) # pragma pop_macro("or") #endif ____________________________________________________________________________________ Want to start your own business? Learn how on Yahoo! Small Business. http://smallbusiness.yahoo.com/r-index

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Re: [Boost-users] Boost Lambda Newbie question
by Haroon Khan 30 Nov '06

30 Nov '06

Hi, I'm experimenting with the boost lambda library, and I wrote the following code, to go through the vector of numbers and print out statements if the number is greater than 5 or less than 5 int a[]={1,2,3,4,5,6,7,8,9,10,10,9,8,4,7,6,5,4,3,3,1}; std::vector<int> v(a,a+sizeof(a)/sizeof(int)); std::for_each ( v.begin() , v.end() , (if_(_1<5)[ std::cout<<var((boost::format("%d is less than 5\n")%_1).str()) ].else_[ std::cout<<var((boost::format("%d is greater than 5\n")%_1).str()) ]) ); The boost::basic_format::operator % code gives an assertion since the object that is being passed is the placeholder object, and not the current value. Is there a correct way of doing this? Thanks, Haroon

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