January 2012 - Boost-users - lists.preview.boost.org

[asio] Error "File exists" at connect
by Arash Abghari 20 Jan '12

20 Jan '12

Hi everybody, I am running a server and client using boost::asio. There are 10 clients sending requests simultaneously to the server. Sometimes one of the clients returns the error "File exist" when ip::tcp::socket::connect() is called. Do you have any idea what possibly could cause this error? Thanks, Arash

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Using filesystem::remove with wildcards
by toran 20 Jan '12

20 Jan '12

I am having trouble deleting files with boost::filesystem. Following code does not work for me (and I can't find the doc that explains how to do it). boost::filesystem::path pt("somepath"); pt /= ("*.data"); boost::filesystem::remove(pt); pt variable points to the valid set of files, but removal does not happened. I will appreciate an advise and may be pointing me to the right place in the docs. Thanks.

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Using shared_ptr with reference_wrapper
by Kelvin Chung 19 Jan '12

19 Jan '12

I am currently in the middle of a wrapper conundrum. I currently have the following: template <class Key, class Container> class ContainerWrapper { Container container; public: typedef Key key_type; protected: virtual const typename Container::key_type& mapKey(const key_type&) = 0; }; The idea of ContainerWrapper is that I want to disguise one Key type as another key type. But the following wrapper, intended to present a container of Key pointers as a container of Keys, presents a dangling reference problem: template <class Key, class Container> class HeapKeyWrapper : public ContainerWrapper<Key, Container> { // Container::key_type == boost::shared_ptr<Key> public: typedef Key key_type; protected: // Ignore the lack of boost::const_pointer_cast<Key>() below. The dangling reference is from the fact // that shared_from_this() doesn't return a reference. const boost::shared_ptr<Key>& mapKey(const key_type& key) { return key.shared_from_this(); } }; If I try to fix this by having mapKey() return by value, then this other wrapper breaks: template <class Key, class Container> class IdentityWrapper : public ContainerWrapper<Key, Container> { public: typedef Key key_type; protected: // Assume Key extends boost::enable_shared_from_this<Key>. // Returning by value would mean the returned value is a copy of key, and not the original // so calling shared_from_this() from the mapped key would break, say const Key& mapKey(const key_type& key) { return key; } }; I'm trying to fix the code so that both wrappers work (short of refactoring the mapKey() functionality to a functor of some sort), which leads me thinking about using boost::reference_wrapper in some way. (The problem that I have is that I could have IdentityWrapper::mapKey() return a reference_wrapper, but that violates the mapKey() interface.) This has also led me down to a related path - what if I changed my backing container to use reference_wrapper instead of shared_ptr? It seems to be that it is ill-advised: the container technically isn't holding the object, and so the objects in the container could be deallocated in the meantime, leaving me with containers full of dangling references. I have valid uses of both HeapKeyWrapper and IdentityWrapper elsewhere in my code, so what do you think should be the right choice given this dangling reference problem currently present in HeapKeyWrapper?

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[Chrono] Is there any functions that convert Chrono's time_point and duration to their Ptime equivalents?
by Matthew Jenks 19 Jan '12

19 Jan '12

Hello, I have been trying to find in the boost libraries if there are any interoperability functions for Boost::Chrono and Boost::Posix_Time? Does anyone know if they exist and what class they are in? Thanks, Matt

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adjacency lists
by Neiderer, Andrew M CIV (US) 19 Jan '12

19 Jan '12

I am still learning graphs, BGL 1.48.0 so beginner questions: 1. not sure what adjacency list/matrix are used for other than building a graph for traversal. Or maybe this is it? 2. I need to build a sparse network. So I am using adjacency_list_io.cpp by Francois Faure (2001). In this example I can read(g2), but when outputting std::cout << write(g2) I get lots of translation errors :-( I know I do not give details here but maybe someone could guess a -D??? to make adjacency_list_io.hpp happy. (The read(g2) works fine) Or I can certainly provide some of the error message. Also has Dr. Nick Edmonds completed (or near completion) of "active-message" based release (MPI)? Thank you. Andrew M. Neiderer US Army Research Laboratory

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Boost-build targets order
by Jarosław Bober 19 Jan '12

19 Jan '12

Hello i have a quick question regarding targets in boost-build jamfiles. Let's say i have 3 targets defined in my jamroot and then I say: bjam target1 target2 target3 Is the order of building targets defined somehow? Regards

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boost::thread and helgrind
by Frederick Roth 19 Jan '12

19 Jan '12

I am currently fooling around with boost::thread. After writing a short example program (featuring boost::thread and boost::interprocess::interprocess_semaphore), I ran helgrind against it and got some "Possible data race" errors. The program does nothing but start two threads and serialize them via the semaphore and I am unsure whether a) I did some error I am not aware of b) helgrind reports false positives I would be glad if someone could look at my code (attached) and give me a hint. Frederick Roth PS: Software versions are boost-1.47.0, valgrind-3.6.1, gcc 4.6.2, c++0x

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Newbie, just starting.
by Robillard, Greg L 18 Jan '12

18 Jan '12

I am trying to get my boost libraries up and running, so I can start using the test framework. When running: #define BOOST_TEST_MODULE const_string test #include <boost/test/unit_test.hpp> // EOF I get the following error: xlC_r -I /home/.../BoostTest/boost_1_48_0 newTest.cpp -o newTest ld: 0711-317 ERROR: Undefined symbol: boost::unit_test::__vftQ3_5boost9unit_test15unit_test_log_tQ3_5boost9unit_test13test_observer ld: 0711-317 ERROR: Undefined symbol: .boost::unit_test::framework::master_test_suite() ld: 0711-317 ERROR: Undefined symbol: .main ld: 0711-345 Use the -bloadmap or -bnoquiet option to obtain more information. Alternately, when I try to run: #include <boost/lambda/lambda.hpp> #include <iostream> #include <iterator> #include <algorithm> int main() { using namespace boost::lambda; typedef std::istream_iterator<int> in; std::for_each( in(std::cin), in(), std::cout << (_1 * 3) << " " ); } I receive the following error: "/home/.../BoostTest/boost_1_48_0/boost/lambda/detail/function_adaptors.hpp", line 29.1: 1540-0063 (S) The text ">" is unexpected. Any assistance would be great. Greg

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boost::split_regex
by Brad Tilley 18 Jan '12

18 Jan '12

I'm experimenting with boost::split_regex and ran into an issue. The first three examples (results1, results2, results3) compile and work as expected. The last one (results4) does not compile. Here's the code I'm using: std::string str1("hello abc-ABC-aBc goodbye"); static const boost::regex re("-ABC-"); std::vector<boost::iterator_range<std::string::iterator> > results1; boost::ifind_all( results1, str1, "abc" ); std::vector<boost::iterator_range<std::string::iterator> > results2; boost::split(results2, str1, boost::is_any_of("-")); std::vector<std::string> results3; boost::split_regex(results3, str1, re); std::vector<boost::iterator_range<std::string::iterator> > results4; // compile error on this line: boost::split_regex(results4, str1, re); I've read the documents here: http://www.boost.org/doc/libs/1_48_0/doc/html/boost/algorithm/split_regex.h… and I believe my usage of split_regex is correct? It compiles and works with std::string (results3) but not with boost::iterator_range. The compiler error is long and verbose, so I'm hesitant to post it here. I was hoping that someone could look at the usage example I provided and see how I'm doing it wrong. I prefer iterator_range as it does not make a copy. Thanks for any advice! Brad

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Re: [Boost-users] how to calculate the Sample standard deviation using accumulators
by Victor Yankee 18 Jan '12

18 Jan '12

Hello Marshall, >On Jan 17, 2012, at 3:38 PM, Victor Yankee wrote: > >> How can I calculate the Sample Standard Deviation over a std::vector of doubles using accumulators? >> >>Or is there a faster way in boost math or some such? > > >Google is your friend (second hit for "boost accumulator standard deviation"): > http://stackoverflow.com/questions/7616511/calculate-mean-and-standard-devi… >and http://stackoverflow.com/questions/4316716/is-it-possible-to-use-boost-accu… > > > accumulator_set<double, stats<tag::variance> > acc; > for_each(a_vec.begin(), a_vec.end(), bind<void>(ref(acc), _1)); > > cout << mean(acc) << endl; > cout << sqrt(variance(acc)) << endl; But this is the POPULATION standard deviation (variance divided by N) I think. What I was asking for was how to calculated the SAMPLE standard deviation (variance devided by N-1). Thanks, Vic

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