December 2013 - Boost - lists.preview.boost.org

Re: [boost] [atomic] Probable documentation issue: how do we know atomic is safe and/or efficient?
by Pete Bartlett 24 Dec '13

24 Dec '13

> On 24 Dec 2013, at 13:43, "John Maddock" <john(a)johnmaddock.co.uk> wrote: > > This message has no content.

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Ominous Warning — should I be worried?
by John M. Dlugosz 23 Dec '13

23 Dec '13

I'm compiling with VS10, and using Boost 1.49.0 “reference member is initialized to a temporary that doesn't persist after the constructor exits” That does not sound good, and browsing through the mailing list archives I see discussions of regressions in 2010 that cite C4413 and use of emplace. I can't read the source code because it's just a ball of preprocessor stuff. Is this a real problem or a warning that can be ignored? I would think that if Boost.Container was broken on VS10, it would be mentioned somewhere where it's easy to spot. Thanks, —John E:\boost_1_49\boost/preprocessor/iteration/detail/local.hpp(37): warning C4413: 'boost::container::container_detail::advanced_insert_aux_non_movable_emplace1arg<A,Iterator,P0>::m_p0' : reference member is initialized to a temporary that doesn't persist after the constructor exits with [ A=std::allocator<std::tr1::shared_ptr<MyTypeA>>, Iterator=std::tr1::shared_ptr<MyTypeA> *, P0=std::tr1::shared_ptr<MyTypeA> ] E:\boost_1_49\boost/preprocessor/iteration/detail/local.hpp(37) : see declaration of 'boost::container::container_detail::advanced_insert_aux_non_movable_emplace1arg<A,Iterator,P0>::m_p0' with [ A=std::allocator<std::tr1::shared_ptr<MyTypeA>>, Iterator=std::tr1::shared_ptr<MyTypeA> *, P0=std::tr1::shared_ptr<MyTypeA> ] E:\boost_1_49\boost/preprocessor/iteration/detail/local.hpp(37) : while compiling class template member function 'boost::container::container_detail::advanced_insert_aux_non_movable_emplace1arg<A,Iterator,P0>::advanced_insert_aux_non_movable_emplace1arg(A &,P0 &&)' with [ A=std::allocator<std::tr1::shared_ptr<MyTypeA>>, Iterator=std::tr1::shared_ptr<MyTypeA> *, P0=std::tr1::shared_ptr<MyTypeA> ] E:\boost_1_49\boost/preprocessor/iteration/detail/local.hpp(37) : see reference to class template instantiation 'boost::container::container_detail::advanced_insert_aux_non_movable_emplace1arg<A,Iterator,P0>' being compiled with [ A=std::allocator<std::tr1::shared_ptr<MyTypeA>>, Iterator=std::tr1::shared_ptr<MyTypeA> *, P0=std::tr1::shared_ptr<MyTypeA> ] E:\boost_1_49\boost/preprocessor/iteration/detail/local.hpp(37) : see reference to class template instantiation 'boost::container::container_detail::advanced_insert_aux_emplace1arg<A,Iterator,P0>' being compiled with [ A=std::allocator<std::tr1::shared_ptr<MyTypeA>>, Iterator=std::tr1::shared_ptr<MyTypeA> *, P0=std::tr1::shared_ptr<MyTypeA> ] mysourcefile.cpp(172) : see reference to function template instantiation 'void boost::container::vector<T>::emplace_back<std::tr1::shared_ptr<_Ty>>(P0 &&)' being compiled with [ T=std::tr1::shared_ptr<MyTypeA>, _Ty=MyTypeA, P0=std::tr1::shared_ptr<MyTypeA> ]

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Beginner
by prabhdeep singh 23 Dec '13

23 Dec '13

I want to start contributing to the open source community, but I do not where to begin. Your community's cause seems great! So I would love to start but I am absolutely clueless as to where to begin. I have a background in C++ and algorithmic operations. Any help would be appreciated!

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[git] Effects of git submodule update
by Beman Dawes 23 Dec '13

23 Dec '13

There has been a lot of concern expressed about updating submodules, so I've updated the applicable section of "Getting Started with Modular Boost Library Maintenance" to include reassurance that uncommitted changes will not be overwritten. See https://svn.boost.org/trac/boost/wiki/StartModMaint A table has been added describing the effects of git submodule update. Actual tests were run to determine the effects, using git 1.8.2.msysgit.0. See https://svn.boost.org/trac/boost/wiki/StartModMaint#Effectsofgitsubmoduleup… In looking at the table, a couple of things stand out: * git submodule update, like git checkout, will not normally overwrite uncommitted changes, regardless of whether the working copy is detached or on a branch. See the table for the specific error message. From the error message it appears checkout may actually be being called. * The case of an update applied to a submodule that is on branch master and at a commit behind the super-project's commit for that submodule just does a pull without a detach. That is the only case where a" checkout --detach" isn't done before a pull. I'm unsure whether this is a feature or a bug. Comments welcome, --Beman

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generating documentation in modular boost
by Peter A. Bigot 23 Dec '13

23 Dec '13

I'm trying to update documentation in lib/utility but can't see how to regenerate the html files. Generalizing from the fact I can run the tests by invoking b2 within the module test subdirectory, I invoked b2 from within the doc subdirectory. This produced an error about an unknown feature "<format>" in Jamfile.v2. When I comment out those lines I do get xml files generated in a subdirectory of the superproject, but I expected html, matching what's been checked in. Is there documentation on building documentation that I haven't been able to find? Peter

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Serializing a Graph Structure Using Boost
by Nouf M. 23 Dec '13

23 Dec '13

Hi, I would like to use boost to serialize my graph (it's in the boost adjacency list format)... I couldn't do it... I managed to serialize an array and some other structures as follows: int I[5] = {0,1,2,3,4}; boost::archive::text_iarchive ia(file), ia << I; but that doesn't work with graph data in the boost adjacency list format... when I write: ia << g //g is my graph I get the following compilation error: 'serialize' is not member of 'VertexProperties' 'VertexProperties' is a structure that I wrote as follows: struct VertexProperties { int id; int weight; }; I don't know how to add 'serialize' as a member function... I also tried "SavingArchieve" template but couldn't do it... Any idea's please? or references?

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Access is denied for the "bootstrap" command
by Nouf M. 23 Dec '13

23 Dec '13

Hi, In order to use the serialization files... I need to build them... I have to go to the BGL directory from the command prompt and enter the "bootstrap" command... It works on some machines... But on my machine it gives me: "Building Boost.Build engine Access is denied. Failed to build Boost.Build engine. Please consult bootstrap.log for further diagnostics" My machine is an HP Workstation and I'm using Windows 7 professional edition... Why do you think I'm getting Access is denied?

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[type_traits] is_empty fails on final classes.
by yuri kilochek 22 Dec '13

22 Dec '13

Hi. It seems boost::is_empty uses Empty Base Optimisation to detect whether a class type is stateless or not. This predictably fails on final types, as they cannot be inherited from: #include <iostream> #include <boost/type_traits.hpp> class Test final {}; int main() { std::cout << boost::is_empty<Test>::value; return 0; } Fails on gcc 4.8.1 with In file included from /usr/local/include/boost/type_traits.hpp:54:0, from main.cpp:2: /usr/local/include/boost/type_traits/is_empty.hpp: In instantiation of 'struct boost::detail::empty_helper_t1<Test>': /usr/local/include/boost/type_traits/is_empty.hpp:79:5: required from 'const bool boost::detail::empty_helper<Test, true>::value' /usr/local/include/boost/type_traits/is_empty.hpp:88:5: required from 'const bool boost::detail::is_empty_impl<Test>::value' /usr/local/include/boost/type_traits/is_empty.hpp:220:1: required from 'struct boost::is_empty<Test>' main.cpp:7:39: required from here /usr/local/include/boost/type_traits/is_empty.hpp:52:8: error: cannot derive from 'final' base 'Test' in derived type 'boost::detail::empty_helper_t1<Test>' struct empty_helper_t1 : public T ^ Yet std::is_empty works just fine (al least in gcc), and appears to be implemented via an intrinsic: template<typename _Tp> struct is_empty : public integral_constant<bool, __is_empty(_Tp)> {}; Now, is it at all possible to implement conforming is_empty without resorting to compiler magic that are intrinsics?

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[git] How the blazes are you supposed to update all the submodules?
by John Maddock 22 Dec '13

22 Dec '13

OK.... so I do a Git pull at the top level (note: using TortoiseGit), and I see lots of messages in the log indicating which libraries have updates, and judging by the time taken they seem to be downloaded (?), but I don't actually see any changes in the libraries themselves. BTW I have every library set explicitly to either "develop" or "master". If I do a "git pull" on an individual library then the changes do come through OK. So what's the right way to do this? I assume it's not a "submodule update" as that seems to leave everything in a detached head state which I take it is a bad idea? I'm also seeing a lot of negative comments about Git submodules on the web, for example: http://codingkilledthecat.wordpress.com/2012/04/28/why-your-company-shouldn…, seems like there's a lot of potential to shoot yourself in the foot/head/chest here? Thanks, John.

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Storing an adjacency list
by Nouf M. 22 Dec '13

22 Dec '13

Hi, I have a very large graph data (150000 node and 450000 edges) in two text files... first one: contains the vertices and their weights. second one: contains the edges and their weights. I need to retrieve a small subgraph from this big graph data...it's easier to do that if the graph is stored in an adjacency list format... I managed to write some code that reads from the files and creates a graph in an adjacency list format... Now, I would like to store the graph (the one in the adjacency list format) for next uses because it takes long time to convert my graph text files into the adjacency list format... I couldn't figure out how to do it... I saw the section about graph I/O in the BGL documentation: Graphviz, Max-flow, and GraphML but I don't think they will do what I need... I looked also on Serialization, I'm not sure about it... will serialization work well to store very large graphs and then retrieve then very fast ... Is this possible? Best regards, Nouf

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