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C++Now 2106 Call for Submission
by Jon Kalb 05 Jan '16

05 Jan '16

Boost Users, The Call for Submissions for C++Now 2016 (AKA BoostCon) has been released: http://cppnow.org/2016-conference/announcements/2015/11/17/call-for-submissi on.html The deadline for submitting is very near and cannot be extended, so don¹t delay your submission. The conference will be held in Aspen the week of May 9th. See you in Aspen! Jon

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[boost][review][qvm] QVM formal review result
by Adam Wulkiewicz 04 Jan '16

04 Jan '16

Dear Boost community, The review period for Emil Dotchevski's QVM library has concluded. I'd like to thank everyone who participated in the discussions, esspecially those who sent formal reviews. Only four votes were casted however more people commented on issues on the mailing list. Comments received during the course of the review were generally positive, with a number of technical issues identified that need to be addressed. The review identified no fundamental problems in the design or implementation of the library that would entail rejection. The final version of the library can be fully accepted once Emil has addressed the issues identified during the review. Therefore I'm happy to say: Emil Dotchevski's Boost.QVM library is CONDITIONALLY ACCEPTED. Full report can be found here: http://lists.boost.org/Archives/boost/2016/01/227027.php Regards, Adam

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[Boost::Python]
by Eugenio Bargiacchi 03 Jan '16

03 Jan '16

Hello everyone, I have a member function with signature const Matrix2D & foo const (); Which returns an internal data structure. Matrix2D is using Matrix2D = Eigen::Matrix<double, Eigen::Dynamic, Eigen::Dynamic, Eigen::RowMajor | Eigen::AutoAlign>; I have explicitly set a to_python converter for Matrix2D, and I have exported the function with a call policy of return_internal_reference. However, when this function is called from Python I get TypeError: No Python class registered for C++ class Eigen::Matrix<double, -1, -1, 1, -1, -1> This happens also if the reference is not const. At the same time, if I modify the call policy to return_value_policy<copy_const_reference>() Python can decode the matrix just fine. The same holds true if I return the Matrix2D by value. However I really need to have a reference to the matrix in order store it into other classes. How can I make Python see the data structure through the reference? The converter in case it is needed: boost::python::list toPythonList(const double * data, size_t num) { boost::python::list list; for (size_t i = 0; i < num; ++i) list.append(data[i]); return list;} struct Matrix2DToPython{ static PyObject* convert(Matrix2D const & m) { boost::python::list list; for (int i = 0; i < m.rows(); ++i) { list.append(toPythonList(m.row(i).data(), m.cols())); } return boost::python::incref(list.ptr()); }}; Thanks, Eugenio

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[units] Adding two absolute units
by Itzik 03 Jan '16

03 Jan '16

Hello, <obligatory appreciation on first post> I started using Boost just for boost::units and I find new ways boost can help me almost every day. So thanks for the great stuff! </obligatory appreciation on first post> My question to the board is why two absolute quantities (si::temperature (K) in my case) can't be summed in boost::units? I realized that this is a rule enforced by-design (gmane.comp.lib.boost.user/71747), and I understand that it is probably not a very common case, but I wanted my code to solve a simple formula which requires adding up two absolute temperatures (quantity<absolute<temperature>>). Each temperature represents an Inlet temperature in a Heat Exchange system. So even if converting one temperature to a relative type (quantity<temperature>) might be a workaround, it seems like a forced misuse to me. Eventually it turned out that I was mistaken with the formula, and subtraction was required instead, so there's no problem there. Alas, there's also a much simpler use case: What if I want to average the temperature of the last N readouts? Shouldn't boost::units support this simple operation? I have no formal physics education, but intuitively, adding two absolute temperatures doesn't seem really like a mistake to me, even if it's an odd thing to do. Will appreciate your thoughts on the matter.

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Modifying all matching elements in a Boost.MultiIndex Container
by Amit Prakash Ambasta 01 Jan '16

01 Jan '16

Hi, I am trying to modify members of all elements matching value for a given index in a boost.multiindex container index.modify( index.find(value), [](T& element) { ... } ) seems to update a singular element(first match) On the other hand, std::pair<index::iterator, index::iterator> iter = index.equal_range(value); while(iter.first != iter.second) { index.modify( iter.first, [](T& element) { ... } ); iter.first++; } leads to segfaults and unexpected behavior. What would be right way to approach this?

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Pointer to objects in Boost.MultiIndex
by Amit Prakash Ambasta 01 Jan '16

01 Jan '16

Consider the following code snippet: #include <iostream> #include <boost/multi_index_container.hpp> #include <boost/multi_index/ordered_index.hpp> #include <boost/multi_index/member.hpp> using namespace std; using namespace boost::multi_index; struct LinkList; struct LinkList { size_t index; LinkList* parent; LinkList(size_t index, LinkList* parent) : index(index), parent(parent) {} }; struct llindex {}; typedef ordered_unique<tag<llindex>, member<LinkList, size_t, &LinkList::index> > LinkListIndex; typedef boost::multi_index_container<LinkList, indexed_by<LinkListIndex> > IndexedLinkList; template <typename T> void show(T& iterable) { for(auto const& element: iterable) { if(element.parent != nullptr) { std::cout << "Index<" << element.index << ">: " << element.parent->index << std::endl; } else { std::cout << "Index<" << element.index << ">: " << "NULL" << std::endl; } } } int main() { IndexedLinkList ill; auto &index_ll = ill.get<0>(); ill.insert(LinkList{0, nullptr}); ill.insert(LinkList{1, (LinkList*)(&(*index_ll.find(0)))}); ill.insert(LinkList{2, (LinkList*)(&(*index_ll.find(0)))}); ill.insert(LinkList{3, (LinkList*)(&(*index_ll.find(2)))}); show(ill); return 0; } Would (LinkList*)(&(*index__ll.find(value))) be the recommended way to fetch the pointer to parent?

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[BGL] Are normal and reverse undirected edges the same or different?
by Ireneusz Szcześniak 01 Jan '16

01 Jan '16

Hi, In an undirected graph, we create an undirected edge: add_edge(a, b, g); We get the reverse of that edge: edge(b, a, g); Now, are these two edges the same or different? vIf I compare them with the == operator, they are equal, but they have different source and target vertexes. Can I count on this behavior? Will it stick? I'm asking because I couldn't find it in the documentation. Please find attached my unit test. On Debian Jessie, I'm compiling it with: g++ test.cc -l boost_test_exec_monitor -l boost_unit_test_framework -o test Thanks & best, Irek

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[Boost.Serialization][Boost.Iterators] Problem with Boost 1.59.0 in Solaris with SunCC
by dariomt＠gmail.com 30 Dec '15

30 Dec '15

Hi all, I have found a problem compiling Boost, in libs/serialization/src/basic_text_oprimitive.cpp the usage of boost::iterator::iterator_facade is problematic. I have reduced it to a two line minimal case: #include <boost/archive/iterators/ostream_iterator.hpp> boost::archive::iterators::ostream_iterator<char> it; Trying to compile this with SunCC 5.10 (Sun Studio 12.1) in Solaris I get the following error: "boost/iterator/iterator_facade.hpp", line 779: Error: value is not a member of boost::iterators::detail::is_traversal_at_least<std::output_iterator_tag, boost::iterators::bidirectional_traversal_tag>. "boost/archive/iterators/ostream_iterator.hpp", line 40: Where: While specializing "boost::iterators::iterator_facade<boost::archive::iterators::ostream_iterator<char>, char, std::output_iterator_tag, boost::archive::iterators::ostream_iterator<char>&, int>". "boost/archive/iterators/ostream_iterator.hpp", line 40: Where: Specialized in boost::archive::iterators::ostream_iterator<char>. "fail.cpp", line 2: Where: Specialized in non-template code. I guess it must be some bug in the compiler, because if I try to instantiate directly the template mentioned in the error message it works fine. (i.e. value is indeed a member). #include <boost/iterator/iterator_facade.hpp> const bool value = boost::iterators::detail::is_traversal_at_least< std::output_iterator_tag, boost::iterators::bidirectional_traversal_tag >::value; For reference, this problem was *not* present in Boost 1.55.0. Thanks! PS: I have mentioned both libraries in the subject because I don't know if this is a problem with Boost.Iterator code, or with the usage of that library from Boost.Serialization.

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[iostreams] Fix for Ticket #11860
by Gagan Kumar 28 Dec '15

28 Dec '15

Bug Ticket ( https://svn.boost.org/trac/boost/ticket/11860 ) says "Using iostreams causes lots of messages about deprecated header template_arity_spec.hpp". Thus to reduce messages about deprecated header, I created a pull request here https://github.com/boostorg/iostreams/pull/24 . Regards Gagan

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Implementation Of Natural Sort for C++
by Gagan Kumar 27 Dec '15

27 Dec '15

In Boost Trac, I found Natural Sort as Ticket #11021 (new Feature Requests). I too think it will be good for C++ to have it too. Thus I tried to make my Implementation on Natural Sort. Here, https://github.com/scopeInfinity/NaturalSort Can this be included in Boost extensions, or can you please guide me to make it better so that It can be included. Regards Gagan Kumar Natural Sort Example - Inputs : Hello 100 Hello 34 Hello 9 Hello 25 Hello 10 Hello 8 Normal Sort Output : Hello 10 Hello 100 Hello 25 Hello 34 Hello 8 Hello 9 Natural Sort Output : Hello 8 Hello 9 Hello 10 Hello 25 Hello 34 Hello 100 | | | | | | | | | | | scopeInfinity/NaturalSortNaturalSort - C++ Implementation of Natural Comparision and Natural Sort | | | | View on github.com | Preview by Yahoo | | | | |

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