August 2015 - Boost-users - lists.boost.org

Log: Overwrite format of sink
by Florian Lindner 14 Aug '15

14 Aug '15

Hello, I have a console sink: boost::log::add_console_log(std::cout, keywords::format = fmtStream); with fmtStream being an expressions stream. After setting up the sinks I load a configuration file: std::ifstream file("log.settings"); init_from_stream(file); Is there a way to overwrite the format of this sink from within in the configuration file. Or, alternatively disable this sink. What I want to achieve is that a user have the option to modify the format without having two console outputs... Thanks, Florian

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Query regarding interest in my submitting plf::colony to Boost
by Soul Studios 14 Aug '15

14 Aug '15

Hi all, I've had some expressions of support outside of the Boost community for submission of the plf::colony container and it's associated container plf::stack, mainly from the review judges for my cppcon submission on the same topic (topic didn't make it through to the finals but got a positive response). I'd like to guage reactions here to see whether it is worth spending the time necessary to port it to Boost, with all the associated reviews etc. plf::colony is a container for unordered data, where erasure and addition do not cause iterator/pointer invalidation, with superior performance characteristics to all std:: containers when either (a) Pointers and iterators which point to container elements must stay valid regardless of container additions and deletions and/or (b) Additions to or deletions from the container will be occurring in performance-critical code. Erasure performance in particular can be in advance of 6000x of vectors, while still being faster than lists, maps, deques etc for add and iteration. Full details and benchmarks across four compilers are here: http://www.plflib.org/colony.htm#benchmarks It has been thoroughly tested, including integrating it into the game engine I constructed last year as well as the usual unit tests. It supports both C++0x and C++11, and has been tested on the following compilers so far: Clang 3.4, GCC 4.6, 4.7, 4.8, 4.9 and 5.1 (both 32-bit and 64-bit), MS Visual C++ 2010 & 2013 (2015 supported but untested as yet). Internally a colony is a combination of a linked-list of increasingly-larger memory blocks combined with boolean erasure fields, combined with a custom memory location recycle stack. The most common comment I get is "that sounds kinda like a deque", so to save some time here are the differences (from the FAQ): "A double-ended queue requires a very different internal framework. It may or may not use a linked-list of memory blocks, dependent on the compiler, and has no comparable performance characteristics. Deque element erasure is very slow, similar to a vector, and it does not free unused memory blocks to the OS once they are empty, unlike a colony. In addition a deque invalidates references to subsequent container elements when erasing elements, which a colony does not. A colony never invalidates pointers/iterators to elements unless the element being referred to is erased." The rest of the faq is here and I would appreciate it if people read it before casting judgement: http://www.plflib.org/colony.htm I am aware that it will be a lot of work to port colony to Boost, so I will only undertake this if there is genuine interest. In addition, plf::stack - which colony must use internally - is a std::stack equivalent container but with much better performance characteristics, which can be used outside of plf::colony. Asides from the performance characteristics, colonies have the following positive and negative properties: Positive: Lack of pointer/iterator invalidation makes interrelating between collections of data easier, without the cache misses associated with vectors of pointers to dynamically-allocated objects. Negative: Due to the additional overhead, performance can be worse for scalar types. Thanks in advance- Matt B

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[units] Conversions from quantities
by Michael Powell 14 Aug '15

14 Aug '15

Hello, Just wanted to clarify something. These should convert from given quantities to the desired units? double unit_conversion::from_length_to_inches(quantity<length> const & L) { const quantity<inch_base_unit::unit_type> result_(L); return result_.value(); } double unit_conversion::from_mass_to_pounds(quantity<mass> const & M) { const quantity<ounce_base_unit::unit_type> result_(M); return result_.value(); } >From an earlier post, I think maybe so, but I was interested in expert opinions, as well. https://groups.google.com/forum/#!topic/boost-list/YDJoMcu1Xx4 Thank you... Best regards, Michael Powell

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Boost 1.59.0 has been released
by Marshall Clow 13 Aug '15

13 Aug '15

Release 1.59.0 of the Boost C++ Libraries is now available. These open-source libraries work well with the C++ Standard Library, and are usable across a broad spectrum of applications. The Boost license encourages both commercial and non-commercial use. This release contains two new libraries and numerous enhancements and bug fixes for existing libraries. New Libraries * Convert: An extendible and configurable type-conversion framework, from Vladimir Batov. * Coroutine2: from Oliver Kowalke For details, including download links, see http://www.boost.org/users/news/version_1.59.0 You can also download directly from SourceForge: http://sourceforge.net/projects/boost/files/boost/1.59.0/ To install this release on your system, see http://www.boost.org/doc/libs/release/more/getting_started/index.html Thanks, --The Boost release team Vladimir Prus Rene Rivera Marshall Clow Eric Niebler Daniel James Beman Dawes

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[Interprocess][Container] nested containers and scoped allocators
by Malko 13 Aug '15

13 Aug '15

Hi, First of all my setup: I am compiling on redhat 6 with clang 3.4 in C++03, using boost_1_58. In a project of mine I am using a map<int, vector<int>> (types to be stored in shared memory and I am using the proper allocators as per interprocess documentation). If mymap is an instance of such a type, then mymap[0] is an invalid syntax because of issues that, to the best of my understanding, are related to the fact that the map tries to use the default constructor (with the default allocator) for the nested type as operator[] also accounts for the case in which the entry is missing and must be constructed. Using at() instead of operator[] makes the whole thing compile. On construction, I give the usual instance of allocator<void, segment_manager> to mymap. According to what I read in Boost.Container docs: http://www.boost.org/doc/libs/1_58_0/doc/html/container/Cpp11_conformance.h… It would seem to me that a scoped allocator is a mechanism by which the allocator I gave to mymap is passed down to the nested vector. In which case I would expect operator[] to try to use such allocator instead of the default one. But then again, I always do mymap.insert(std::pair<const int, vector<int,...>>(0, vector<...>(my_void_alloc))) to add an element to the map, since I need to specify the allocator (and the examples in interprocess use this syntax). Given all of this, I would be grateful for any insight into the following: 1. If the scoped allocator is meant to be passed from the map to the vector, why can I not use operator[] and I necessarily need to use insert() to create a new vector in the map? Have I misunderstood what a scoped allocator is? Thanks in advance. -- View this message in context: http://boost.2283326.n4.nabble.com/Interprocess-Container-nested-containers… Sent from the Boost - Users mailing list archive at Nabble.com.

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1.59.0 rc3 is now available
by Marshall Clow 13 Aug '15

13 Aug '15

New Release candidate files for 1.59.0 are available at: http://boost.cowic.de/rc/ RC3 should fix the problem with VC14 and MSPDB140.DLL. As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. This helps ensure the candidates build OK before we push them out to SourceForge. The files (and associated md5s) are: MD5 (boost_1_59_0_rc3.7z) = 0a2e512844f3e30a6240f8139ee983f3 MD5 (boost_1_59_0_rc3.tar.bz2) = 6aa9a5c6a4ca1016edd0ed1178e3cb87 MD5 (boost_1_59_0_rc3.tar.gz) = 51528a0e3b33d9e10aaa311d9eb451e3 MD5 (boost_1_59_0_rc3.zip) = 08d29a2d85db3ebc8c6fdfa3a1f2b83c Thanks! -- The release managers P.S. Release notes are here: http://www.boost.org/users/history/version_1_59_0.html

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[statechart] Events forwarding and orthogonal states
by lucaghera 13 Aug '15

13 Aug '15

Hi all, I've a problem similar to the one discussed in this old post: http://boost.2283326.n4.nabble.com/statechart-Broadcasting-events-to-orthog… I have a state, let's call it A, which contains two orthogonal regions. State X is the initial state of region 0 and state Y is the initial state of region 1. Both state A and state Y have a custom reaction for event E. State Y execute some computation based on event E while state A simply keeps track of how many times the event E is triggered. State A discard the event at the end of the custom reaction, while state Y forward it (the goal would be to forward it to the state A). >From the old post I think I have understood how the statechart library works and why the state Y never receives the event E. I guess that in my case state X is chosen as first state to process event E. Given that X is not interested in event E, the event is forwarded to state A, which process it and discard it. I see few possible solutions (with drawbacks) but I would like to know how this problem should be addressed. 1) I could do the counting directly in the state Y and remove the custom reaction to E from state A. This would work, however if tomorrow I will define a third state Z interested in E, I would have to duplicate the event counting code, which would work only if I assume that the Z and Y are not active at the same time (otherwise the event would be counted twice). 2) I could define an event that is listened only by state A and is triggered by the state Y after processing E. This doesn't seem really elegant and if multiple states are interested in E I have to be careful to not count the event twice. -- View this message in context: http://boost.2283326.n4.nabble.com/statechart-Events-forwarding-and-orthogo… Sent from the Boost - Users mailing list archive at Nabble.com.

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[variant] Possible regression from 1.55 to 1.58
by Mario Lang 12 Aug '15

12 Aug '15

Hi. I just upgraded my Boost from 1.55 to 1.58. My project doesn't build anymore, it fails on the following pattern, which used to work with 1.55: ---<snip>--- #include <algorithm> #include <boost/variant.hpp> #include <string> #include <iostream> #include <vector> struct visitor : boost::static_visitor<std::ostream &> { result_type operator() (int) { return std::cout; } result_type operator() (std::string) const { return std::cout; } }; int main() { std::vector< boost::variant<int, std::string> > v; visitor vis; foreach(v.begin(), v.end(), boost::apply_visitor(vis)); return 0; } ---<snip>--- The example is a bit silly, since foreach discards the return value of apply_visitor anyway. So my solution was to change the visitor to define result_type as void. This works. However, I am wondering why delayed_visitor does no longer work in this situation? Is it because I am trying to return a reference? -- CYa, ⡍⠁⠗⠊⠕

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Problem accessing boost trac
by Leo Carreon 12 Aug '15

12 Aug '15

Hi Boosters, Sorry to be posting this here but I’m trying to access boost trac and I’m getting a certificate error. Does anyone know how to resolve this issue? Regards, Leo

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[intrusive_ptr] Strange ternary op behavior with MSVC14
by TONGARI J 12 Aug '15

12 Aug '15

Hi, I found a strange bug while debugging: This is the minimal example that shows the problem: (the nullptr will be some other meaningful thing in real case) ```c++ #include <iostream> #include <boost/smart_ptr/intrusive_ptr.hpp> #include <boost/smart_ptr/intrusive_ref_counter.hpp> template<class T> struct wrapper { wrapper() = default; wrapper(boost::intrusive_ptr<T> const& p) : _p(p) {} boost::intrusive_ptr<T> const& get_ptr() const { #if 0 // This is OK. if (_p) return _p; return nullptr; #else // Strange behavior. return _p ? _p : nullptr; #endif } private: boost::intrusive_ptr<T> _p; }; struct W : boost::intrusive_ref_counter<W> { }; template<class T1, class T2> inline void test(wrapper<T1> const& s1, wrapper<T2> const& s2) { auto tup = std::make_tuple(s1.get_ptr(), s2.get_ptr()); std::cout << 0 << ":" << (void*)std::get<0>(tup).get() << "\n"; std::cout << 1 << ":" << (void*)std::get<1>(tup).get() << "\n"; } int main() { wrapper<W> a(new W), b(new W); test(a, b); return 0; } ``` If compiled with MSVC14, you'll see the 2 addresses are the same while they shouldn't. If if-stmt is used instead, the problem won't be shown. I also replaced intrusive_ptr with std::shared_ptr and the problem isn't shown as well. The same code works well with g++. It seems intrusive_ptr & MSVC14 specific but I can't reason about... Any idea?

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