April 2005 - Boost-users - lists.preview.boost.org

lambda dereferencing pointer
by Matthias Kaeppler 05 Apr '05

05 Apr '05

Hello, consider m_files to be a vector of pointers to boost::filesystem::pathS: std::partition( m_files.begin(), m_files.end(), boost::bind( &boost::filesystem::is_directory, *boost::lambda::_1 ) ); I want to invoke is_directory on the pointees. The error message is extremely long-winded and expands over several pages. I suppose you don't want to see it :) But maybe you can see immediately what I'm doing wrong? -- Matthias Kaeppler

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[typeof] MSVC-specific implementation added
by Arkadiy Vertleyb 05 Apr '05

05 Apr '05

Hi all, The recently discussed MSVC-specific trick, by Igor Chesnokov, has been added to the BOOST_TYPEOF submission. As a reminder, this implementation compiles much faster, and doesn't require type/template registration. This implementation covers VC6.5/7.0/7.1, but not VC8.0 (where the loophole seems to have been fixed). Please take it in the Boost sandbox file vault, http://boost-sandbox.sourceforge.net/vault/, typeof.zip. Regards, Arkadiy

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[typeof] MSVC-specific implementation added
by Arkadiy Vertleyb 05 Apr '05

05 Apr '05

Hi all, The recently discussed MSVC-specific trick, by Igor Chesnokov, has been added to the BOOST_TYPEOF submission. As a reminder, this implementation compiles much faster, and doesn't require type/template registration. This implementation covers VC6.5/7.0/7.1, but not VC8.0 (where the loophole seems to have been fixed). Please take it in the Boost sandbox file vault, http://boost-sandbox.sourceforge.net/vault/, typeof.zip. Regards, Arkadiy

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[serialization] Problem serializing uninitialized bools
by Andrew B 05 Apr '05

05 Apr '05

Let me first say "thanks" to everyone involved in Boost, particularly the serialization library. I am continuously impressed with the quality of this project. That said, I think I've encountered an issue that I would label as a bug, but perhaps there's something I'm missing. The following code throws/fails in Visual C++ 7.1 debug build. void boolTest() { bool uninitializedBool1, uninitializedBool2; std::ofstream ofs( "booltest.txt" ); boost::archive::text_oarchive oa( ofs, boost::archive::no_header ); oa << uninitializedBool1; oa << uninitializedBool2; ofs.close(); std::ifstream ifs( "booltest.txt" ); boost::archive::text_iarchive ia( ifs, boost::archive::no_header ); ia >> uninitializedBool1; ia >> uninitializedBool2; ifs.close(); } The reason is clear if you look at the contents of booltest.txt: 204 204 Since those bools are uninitialized, VC has written its standard "garbage" to their contents, which gets serialized as a value other than 0 or 1, which is what what the text_iarchive / ifstream would expect to see. I'm not sure if there's a philosophical opposition to supporting serializing uninitialized data, but the other primitives seem to work, and in my experience, it's not unusual to not initialize ever member of a struct before needing to serialize it. Thanks for your time, Andrew

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boost::mpl::transform
by Lemings, Eric B. (Contr) 05 Apr '05

05 Apr '05

What is the result type of transform if the algorithm is given two sequences of different sizes? Thanks, Eric.

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mpl error message on icc
by Stefan Strasser 05 Apr '05

05 Apr '05

this code has always been working on gcc but doesn't on icc, can anyone tell me what's wrong here: typedef mpl::copy<AMplVector,mpl::back_inserter<mpl::vector<AnotherMplVector> > >::type Type; I removed namespace qualifiers and so on from the error message but it's still not very readable: detected during: instantiation of class "mpl::aux::fold_impl<4, First, Last, State, ForwardOp> [with ... /usr/include/boost/mpl/aux_/preprocessed/plain/fold_impl.hpp(115): error: class "mpl::apply2<mpl::inserter<mpl::vector<Element, Declaration, NameDeclaration, Member, MemberClassifier, TemplateDeclaration, TemplateClassifier, MemberTemplateClassifier , Type, Classifier, Class, MemberClass, TemplateClass, MemberClassifierDefinition, ClassifierDefinition, TemplateClassifierDefinition, ClassDefinition, mpl::na, mpl::na, mpl::na>, mpl::push _back<mpl::na, mpl::na>>::operation, mpl::aux::fold_impl<4, mpl::begin<MemberTemplateClassDefinitionImpl::Bases>::type, mpl::en d<MemberTemplateClassDefinitionImpl::Bases>::type, mpl::inserter<mpl::vector<Element, Declaration, NameDeclaration, Member, MemberClassifier, TemplateDeclaration, TemplateClassifier, MemberTemplateClassifie r, Type, Classifier, Class, MemberClass, TemplateClass, MemberClassifierDefinition, ClassifierDefinition, TemplateClassifierDefinition, ClassDefinition, mpl::na, mpl::na, mpl::na>, mpl::push_back<mpl::na, mpl::na>>::state, mpl::inserter<mpl::vector<Element, Declaration, NameDeclaration, Member, Memb erClassifier, TemplateDeclaration, TemplateClassifier, MemberTemplateClassifier, Type, Classifier, Class, Me mberClass, TemplateClass, MemberClassifierDefinition, ClassifierDefinition, TemplateClassifierDefinition, ClassDefinition, mpl::na, mpl::na, mpl::na>, mpl::push_back<mpl::na, mpl::na>>::operation>::state3, mpl ::deref<mpl::aux::fold_impl<4, mpl::begin<MemberTemplateClassDefinitionImpl::Bases>::type, mpl::end<MemberTemplateClassDefinitionImp l::Bases>::type, mpl::inserter<mpl::vector<Element, Declaration, NameDeclaration, Member, MemberClassifier, TemplateDeclaration, TemplateClassifier, MemberTemplateClassifier, Type, Classifier, Class, MemberClass, TemplateClass, MemberClassifierDefinition, ClassifierDefinition, TemplateClassifierDefinition, ClassDefinition, mpl::na, mpl::na, mpl::na>, mpl::push_back<mpl::na, mpl::na>>::state, mpl::inserter<mpl::vector<Element, Declaration, NameDeclaration, Member, MemberClassifier, Te mplateDeclaration, TemplateClassifier, MemberTemplateClassifier, Type, Classifier, Class, MemberClass, Templ ateClass, MemberClassifierDefinition, ClassifierDefinition, TemplateClassifierDefinition, ClassDefinition, mpl::na, mpl::na, mpl::na>, mpl::push_back<mpl::na, mpl::na>>::operation>::iter3>::type>" has no member "type" typedef typename apply2< ForwardOp, state3, typename deref<iter3>::type >::type state4; regards, -- Stefan Strasser

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about enable_if for member functions
by Yutaka Leon Suematsu 04 Apr '05

04 Apr '05

Dear booster, I have a question related to enable_if. I would like to enable or disable some member functions from a template class, but enable_if is -not enable- to do it :-) Here is the code. template <class T> class A { ... enable_if< boost::is_arithmetic<T>, void > :: type f1() { ... } }; In class A, I want to define function f1 only if the template parameter is arithmetic. It works fine except when the parameter is not arithmetic. I have a compile error "error C2039: 'type' : is not a member of 'boost::enable_if<Cond,T>'" (Working with VC7.1, and boost 3.12) Thank you in advance for any suggestions and help. Sincerely yours, Yutaka Leon Suematsu

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Re: Re: STL algorithms & references (David Abrahams)
by Sean DeNigris 04 Apr '05

04 Apr '05

To anyone interested, I ended up writing for_each<cIterType&>(.) and the algorithm passed the iterators by reference. - Sean >typedef set<int>::const_iterator cIterType; >cIterType bit = mySet.begin(); cIterType eit = >mySet.end(); > >for_each(ref(bit), ref(eit), > if_(bind(boost::next<cIterType>, boost::ref(bit)) != mySet.end()) > [...]

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Re: unordered_map has no lower_bound?
by Gottlob Frege 04 Apr '05

04 Apr '05

> Date: Mon, 04 Apr 2005 16:39:34 +0100 > From: Ben Hutchings <ben.hutchings(a)businesswebsoftware.com> > Subject: Re: [Boost-users] Re: unordered_map has no lower_bound? > To: boost-users(a)lists.boost.org > Message-ID: <42515FB6.9040803(a)businesswebsoftware.com> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > Daniel James wrote: > >> Martin Wartens wrote: > >> > >>> PS: there is a small problem in hash_table.hpp causing a warning in > >>> VC7.1 > >>> line 278 should be: > >>> return (*prev_ptr)!=0; > >>> instead of > >>> return *prev_ptr; > > > > > > Ah, I just found out why I didn't do this before - prev_ptr might be a > > pointer object (depending on the allocator), so the correct line is: > > > > return (*prev_ptr) != link_ptr(); > > > > Which can potentially be inefficient. I think the best thing to do is to > > use a pragma to disable the warning, > > If it's the warning I'm thinking of (C4800: "forcing value to bool > 'true' or 'false'" - well, *duh*) then this is the right approach. > > > or maybe: > > > > return static_cast<bool>(*prev_ptr); > > > > or: > > > > return boost::implicit_cast<bool>(*prev_ptr); > > > > would work. > > Neither of those prevents the warning. > > Ben. > I always use !! to prevent that warning. like return !!*prev_ptr; YMMV.

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C++ Template Metaprogramming -- EX 2.1
by Kelly Burkhart 04 Apr '05

04 Apr '05

I'm going through the excercises in this book and am stumped on the second one I tried. Does anyone have a hint on how to approach this problem? TIA, -K

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