February 2015 - Boost-users

[context] boost::coroutines::asymmetric_coroutine<T>::pull_type iterator does not properly model InputIterator
by Mueller-Roemer, Johannes Sebastian 16 Feb '15

16 Feb '15

I’m currently on Boost 1.56 so this might have been fixed by now, but in a simple test Boost.Coroutine fails to properly model the InputIterator concept, because *it++ does not conform to the operational semantics { T tmp = *it; ++it; return tmp; } required by the standard. The failing program: #include <boost/coroutine/asymmetric_coroutine.hpp> #include <iostream> template<typename Continuation> auto foo(Continuation && yield) -> void { yield("Hello"); yield(", "); yield("World"); yield("!\n"); } //using T = char const *; using T = std::string; auto foo() -> boost::coroutines::asymmetric_coroutine<T>::pull_type { using namespace boost::coroutines; return asymmetric_coroutine<T>::pull_type{ [](asymmetric_coroutine<T>::push_type& yield) { foo(yield); } }; } auto main(int, char **) -> int { auto f = foo(); for(auto it = boost::begin(f); it != boost::end(f);) std::cout << *it++; } Which (on my machine) outputs: , World! X☺à r2 ` , ` , Ç2 Ç Failing to model the InputIterator concept is bad, because then it isn’t any kind of standards-conforming iterator at all. Interestingly, if T is char const * and not std::string the program works as expected. Is there some other subtle bug at work here? -- Johannes S. Mueller-Roemer, MSc Wiss. Mitarbeiter - Interactive Engineering Technologies (IET) Fraunhofer-Institut für Graphische Datenverarbeitung IGD Fraunhoferstr. 5 | 64283 Darmstadt | Germany Tel +49 6151 155-606 | Fax +49 6151 155-139 johannes.mueller-roemer(a)igd.fraunhofer.de | www.igd.fraunhofer.de

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Strange boost::threads behaviour
by Lorenzo Trivelli 16 Feb '15

16 Feb '15

Hi to everyone, first of all thanks to all the people who writes and manteins this wondefrul collection of libraries ;-) While analyzing a resource exaustion problem on a production machine, (Windows) I found out astrange behaviour of boost::threads regarding event object. The problem is that after a certain number of iterations it semms that the thread lib allocates an EventHandle which is never freed. I managed to reproduce in some ways the behaviour, but I'm a bit clueless about its reason. To be honest, the amount of handles "leaked" by the test code is quite less than the amount I found on production server, but test code is also quite simpler. Now some info: 1) OS: Win 2033 , Win 2008 2) I tested it with both 1.46.1 and 1.57.0, compiled using stlport using VS2005 3) if you want I can attach the sample code with a but if info on how to reproduce the behaviour thanks in advance L. Trivelli

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[future] Confused about the represents in Doc "boost::future"
by Cheng Mo 16 Feb '15

16 Feb '15

Hi all : I got confused in Doc of boost :: futures and I can't got the point of sort of terms. The represents in Overvies of Futures like " Instances can be freely copied and assigned, and boost::shared_future<R>::get() returns a non const reference so that multiple calls to boost::shared_future<R>::get() are safe." no doubt that a const reference .... are safe. a non const reference could be changed by external stimuli. isn't ? Or the key is "Instances can be freely copied" , so that we can say "are safe"? Cheer~ Martin

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[program options] examples where?
by U.Mutlu 15 Feb '15

15 Feb '15

In the online documentation tutorial there are multiple times mentioned references to the examples page. But where are these examples exactly located? On the documentation pages I couldn't find a link to the examples page. Do I need to install the complete boost developer version locally to get to the examples? -- cu Uenal

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[program options] an alternative for "add_options()" avail?
by U.Mutlu 15 Feb '15

15 Feb '15

Hi, I'm newbie to 'program options'. I just wanted to ask if there is an alternative for the below example from the online-doc: desc.add_options() ("help", "produce help message") ("compression", po::value<int>(), "set compression level") ; I would like to have something more traditional like the following single element addition alternative: desc.add_option("help", "produce help message"); desc.add_option("compression", po::value<int>(), "set compression level"); Is something like this already in the library? -- TIA Uenal

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meta state machine, process_event need to copy given event
by SBAM 13 Feb '15

13 Feb '15

Hello Christophe, I'm a boost msm first time user and I'm attempting to pass an event to my msm that cannot be copied. This event contains a /unique_ptr/ and my goal is to eventually steal it and store it under my msm. However, even with no deferred events, events are /copied/ to an internal queue, in /boost::msm::back::state_machine::do_pre_msg_queue_helper/. I just wanted to know if there was any chance /process_event/ could be overloaded and accept rvalue-ref or if by design, it's absolutely mandatory to copy those events. Many thanks for your great library -- View this message in context: http://boost.2283326.n4.nabble.com/meta-state-machine-process-event-need-to… Sent from the Boost - Users mailing list archive at Nabble.com.

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Performance optimization in Boost using std::vector<>
by saloo 12 Feb '15

12 Feb '15

Hello everybody, I have a question related to performance optimization using Boost. I found this link http://www.boost.org/doc/libs/1_41_0/doc/html/mpi/performance.html <http://www.boost.org/doc/libs/1_41_0/doc/html/mpi/performance.html> and trying to figure out which curve (on the graph in the link) represents the communication of std::vector<int> and std::vector<double>? Is communication using std::vector<int> and std::vector<double> optimized (is_mpi_datatype) or not? So I use "boost_mpi" and "boost_serialization" libraries. I include the header "#include <boost/serialization/vector.hpp>" in my code. Then I send directly std::vector<int> and std::vector<double> using "world.send(...) " and world.recv(...)" calls. I fill the vector with some values (for example I fill ten values) and I get the same ten values on other side of processor boundary. This thing works but I want to improve communication performance. I found out in this link http://www.boost.org/doc/libs/1_57_0/doc/html/mpi/tutorial.html under section "User-defined data types" that "Fixed data types can be optimized for transmission using the is_mpi_datatype type trait. ". Also I studied the information on http://www.boost.org/doc/libs/1_57_0/doc/html/mpi/tutorial.html#mpi.perform…. Also this link http://www.boost.org/doc/libs/1_46_1/libs/serialization/doc/wrappers.html#a… shows that std::vector<> are optimized for serialization. I am now confused that sending std::vector<> like this is good for performance optimization or not? What other better methods are available? Is something like this http://www.boost.org/doc/libs/1_57_0/doc/html/mpi/tutorial.html#mpi.skeleto… a good option? Best Regards, Salman Arshad -- View this message in context: http://boost.2283326.n4.nabble.com/Performance-optimization-in-Boost-using-… Sent from the Boost - Users mailing list archive at Nabble.com.

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Min cut between two vertices, undirected graph
by Mads Jensen 12 Feb '15

12 Feb '15

Hi, The Stoer Wagner implementation only takes as input a complete graph, and then it computes the min cut with the parity map indicating which cut set the vertex belongs to. I need something for computing the minimum cut between two arbitrary vertices given as input for an undirected graph. Edmonds Karps works just for a directed graph. Any help with this will be highly appreciated. -- Med Venlig Hilsen / Kind regards, Mads Jensen Max Jerry Horovitz: "Unfortunately, in America, babies are not found in cola cans. I asked my mother when I was four and she said they came from eggs laid by rabbis. If you aren't Jewish, they're laid by Catholic nuns. If you're an atheist, they're laid by dirty, lonely prostitutes." -- Mary and Max (2009)

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Which URL should I use in ExternalProject_Add
by Yi-Hong Lyu 11 Feb '15

11 Feb '15

Hello all, I used CMake's ExternalProject_Add to download and build boost in my project. The URL I used is ' http://sourceforge.net/projects/boost/files/boost/1.55.0/boost_1_55_0.zip/d…' and it works. However I got an error several days ago like: CMake Error: Problem with archive_read_open_file(): Unrecognized archive format It seems that what I download by CMake becomes 'HTML document, ASCII text' rather than 'Zip archive data, at least v2.0 to extract'. Could you tell me which URL should I use in ExternalProject_Add? Thanks, Yi-Hong

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boost iOS8 failure
by David Medine 11 Feb '15

11 Feb '15

First of all, I know that calls for help are not appropriate to the list, so let me disclaim by saying that I am not asking for help, simply reporting an issue. I am attempting to compile a C++ library (that uses boost) for iOS8 distribution. The library compiles fine on OSX (and Linux and Windows) but will not compile for iOS8. I get dozens of compiler complaints regarding boost headers that all involve some sort of 'Semantic Issue'. For example, in boost's hash.hpp, I get a 'No matching function for call to 'has_value' error on these lines (439-442): | BOOST_HASH_SPECIALIZE_REF(std::string) #if !defined(BOOST_NO_STD_WSTRING) BOOST_HASH_SPECIALIZE_REF(std::wstring) #endif | In this case I was able to skirt the issue by adding code to define the function hash_value for std::string and std::wstring: inline std::size_t hash_value( std::string const &v) { return hash_range(v.begin(), v.end()); } inline std::size_t hash_value( std::wstring const &v) { return hash_range(v.begin(), v.end()); } I am probably going to go through all such failures of clang to interpret the boost code correctly for iOS compilation and modify the source just so I can get this going. This is a major pain because there are dozens of these, many of which are far less straightforward to remedy. Besides I don't necessarily want a custom version of boost that ships with my library. I have the build settings in my iOS project (I'm using XCode) exactly the same as they are in the OSX project. I don't understand why the compiler behaves differently for these two targets. Finally, there are two stackoverflow questions that I posted related to this problem. http://stackoverflow.com/questions/28422862/clang-different-when-compiling-… http://stackoverflow.com/questions/28308466/ios8-boost-hash-hpp-system-cloc… THX!

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