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

[Units] Issue with user defined quantities
by Pieter B. 22 Jan '12

22 Jan '12

LS, I have some problems working with user defined quantities/units in combination with unitless quantities (such as the results of a sin() or cos() operations).Taking the example of the 'nautical mile', which is presented in the documentation: ---START CODE --- namespace nautical { struct length_base_unit : boost::units::base_unit<length_base_unit, length_dimension, 1> { static std::string name() { return "nautical mile"; } static std::string symbol() { return "nmi"; } }; typedef boost::units::make_system<length_base_unit>::type system; typedef unit<length_dimension,system> length; static const length mile,miles; } BOOST_UNITS_DEFINE_CONVERSION_FACTOR(nautical::length_base_unit, boost::units::si::meter_base_unit, double, 1.852e3); ---END CODE --- The following does not compile: ---START CODE --- typedef quantity<boost::units::si::plane_angle> TAngleInRad; typedef boost::units::quantity<nautical::length> TNauticalDistanceInNMI; TNauticalDistanceInNMI NauticalDistanceInNMI; TNauticalDistanceInNMI SumNauticalDistanceInNMI = NauticalDistanceInNMI + NauticalDistanceInNMI; // OK TNauticalDistanceInNMI ScaledSumNauticalDistanceInNMI = NauticalDistanceInNMI + NauticalDistanceInNMI*sin(AngleInRad); // Last line does not compile due to lack of a suitable operator+ ---END CODE --- It does work correctly when using the 'nautical mile' as it has been defined in the library itself in "nautical_mile.hpp" (as a scaled base unit related to the si::meter): ---START CODE --- namespace metric { typedef scaled_base_unit<boost::units::si::meter_base_unit, scale<1852, static_rational<1> > > nautical_mile_base_unit; } // definition of the nautical mile from "nautical_mile.hpp" typedef boost::units::metric::nautical_mile_base_unit::unit_type nautical_mile_unit; typedef quantity<nautical_mile_unit> TNauticalDistanceInNMI; ---END CODE --- However, I don't think I can specify my user-defined units/quantities in this manner as they use a scale factor represented by an arbitrary floating point value. My perception is that the example of the documentation does not work due to the mixing of quantities from the si system (the sin() returns a dimensionless quantity in that system) with user-defined quantities in another ('nautical') system, while the 'nautical mile' from 'nautical_mile.hpp' is a scaled version of the si::meter and thus defined within the realms of the si::system - but please correct me if I am wrong here. My problem can thus be summarized as follows: - the solution from the documentation does not compile - the solution from 'nautical_mile.hpp' uses a scaled base unit which is limited to scaling factors of the form scale<Base,Exponent> and my question is therefore: how can I define my user-defined units/quantities in such a way that they allow the required operations while being related to base units by an arbitrary scale factor? Help would be highly appreciated, Pieter ------------------- Nautical mile version #1 (from the included nautical_mile.hpp): namespace metric { typedef scaled_base_unit<boost::units::si::meter_base_unit, scale<1852, static_rational<1> > > nautical_mile_base_unit; } template<> struct base_unit_info<metric::nautical_mile_base_unit> { static const char* name() { return("nautical mile"); } static const char* symbol() { return("nmi"); } }; typedef quantity<boost::units::si::plane_angle> TAngleInRad; typedef quantity<boost::units::si::length> TDistanceInM; typedef boost::units::metric::nautical_mile_base_unit::unit_type nautical_mile_unit; typedef quantity<nautical_mile_unit> TDistanceInNMI; typedef boost::units::quantity<nautical::length> TNauticalDistanceInNMI; # this is OK: TAngleInRad Angle(0.5*radians); TDistanceInNMI DistanceInNMI; TDistanceInNMI SumDistanceInNMI = DistanceInNMI + DistanceInNMI; TDistanceInNMI ScaledSumDistanceInNMI = DistanceInNMI + DistanceInNMI*sin(AngleInRad); TNauticalDistanceInNMI NauticalDistanceInNMI; TNauticalDistanceInNMI SumNauticalDistanceInNMI = NauticalDistanceInNMI + NauticalDistanceInNMI; TNauticalDistanceInNMI ScaledSum NauticalDistanceInNMI = NauticalDistanceInNMI + NauticalDistanceInNMI*sin(AngleInRad); // DOES NOT COMPILE for lack of a suitable operator+

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[phoenix] [cmath] lazy pow not working in boost 1.48
by alfC 22 Jan '12

22 Jan '12

Hi, Is this a bug in phoenix? the boost::phoenix::pow lazy function doesn't seem to work. My version is Boost 1.48 or maybe 1.49 (after svn update) -- Thanks, Alfredo #include<iostream> #include <boost/phoenix.hpp> #include <boost/phoenix/stl/cmath.hpp> using std::clog; using std::endl; int main(){ using namespace boost::phoenix::arg_names; clog << boost::phoenix::sin(arg1)(1.) << " " << std::sin(1.) << endl; // ok clog << boost::phoenix::pow(arg1, arg1)(2.) << " " << std::pow(2.,2.) << endl; // ^^^^------ error: no matching function for call to ‘pow(const boost::phoenix::expression::argument<1>::type&, double) return 0; }

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Why does boost thread copy a functor?
by Chris Cleeland 22 Jan '12

22 Jan '12

I had code similar to the following... Functor object: struct Task { operator()() { // thread main } smartfd p; }; Note that smartfd is a wrapper around a file descriptor. In its dtor it closes the fd. Then, elsewhere I set up an instance of Task and spawn it with boost::thread... Task t; t.p = // open file descriptor boost::thread thr(t); The spawned thread gets an instance of Task, but it's not the same instance as from the main. What is the rationale? -- Chris Cleeland

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Vote Boost Up for SourceForge Project of the Month
by Dave Abrahams 20 Jan '12

20 Jan '12

Folks, I was just informed that Boost is a top contender for SourceForge's February Project Of The Month. The vote is happening on TwtPoll, here: http://twtpoll.com/7vt4lq It's pretty close, so if you could vote Boost up, it could be good for our profile and our future. Thanks! -- Dave Abrahams BoostPro Computing http://www.boostpro.com

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Re: [Boost-users] Is there any functions that convert Chrono's time_point and duration to their Ptime equivalents?
by Iron Bug 20 Jan '12

20 Jan '12

I found such functions somewhere in boost's sandbox, in chrono development. There're some templates that can be used as examples and adopted for all such conversions. I think, they will be added to chrono, possibly. Look here: http://svn.boost.org/svn/boost/sandbox/chrono/boost/conversion/boost/

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[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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Re: [Boost-users] boost::asio::io_service::postand boost::asio::deadline_timer
by Marat Abrarov 18 Jan '12

18 Jan '12

Hi, Christopher. > I mean > now = current time > "Make biscuits 30 seconds from now." > "Clean the car 10 seconds from now." > "Ride your bike 45 seconds from now." > > Or does posting to the timer before it is "expired" interfere with the first > request? http://www.boost.org/doc/libs/1_48_0/doc/html/boost_asio/reference/basic_de… ~~~~~~~~~ Any pending asynchronous wait operations will be cancelled. The handler for each cancelled operation will be invoked with the boost::asio::error::operation_aborted error code. ~~~~~~~~~ Regards, Marat Abrarov.

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[graph] Query for interest: implicit de Bruijn graph
by Jeremiah Willcock 18 Jan '12

18 Jan '12

Would any Boost.Graph users be interested if I implemented an implicit de Bruijn graph? The graph would have the following benefits and drawbacks: - Would not use any storage, but would act as a d^k-vertex, d^(k+1)-edge (for alphabet size d and word length k) graph. - Would be exactly the de Bruijn graph (with no vertex merging or filtering); those features could be added on top, using filtered_graph and/or another wrapper layer. - A filtered_graph based on a sparse property map could "enable" vertices and edges to process in a given algorithm. - A separate layer could enable processing of chains of vertices together. - I could provide a reverse complement map for the base-4 case, as well as conversions between vertices and edges and strings of the correct length. If anyone is interested, I have a few questions as well: - What should the performance tradeoff be between accessing a vertex's incident edges vs. computing reverse complements? - Does the k-mer size (word length) need to be chosen at run-time, or would a compile-time setting be acceptable? -- Jeremiah Willcock

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Re: [Boost-users] [boost] Proposal for a Differential Evolution C++ library
by P Gregor 18 Jan '12

18 Jan '12

I could also help testing. regards, Piotr

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how to calculate the Sample standard deviation using accumulators Hello,
by Victor Yankee 18 Jan '12

18 Jan '12

Hello, 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 somesuch? Thanks

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boost::asio::io_service::post and boost::asio::deadline_timer
by Christopher 18 Jan '12

18 Jan '12

I am getting boost:asio::error::operation_aborted error codes for an unknown reason in my handlers. No where did a cancel or reset occur, nor was the deadline_time or the io_service destroyed. Does anyone know if I may post to the same io_service a deadline_timer was constructed with or if they will interfere with eachother? May I post multiple times to the deadline timer calling back different methods? I can't imagine why the abort would show up other than I am taking something for granted.

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compiler warnings in
by Chris Cleeland 17 Jan '12

17 Jan '12

Using Boost 1_47_0, in checking some automated builds on a CentOS 4 machine, I get the following errors from the compiler there (gcc v3.4.6). ../../../boost/exception/detail/error_info_impl.hpp:43: warning: `class boost::error_info<tag_answer, int>' has virtual functions but non-virtual destructor Indeed, if I go back and compile the boost tests for exceptions, I get the same compiler warning. GCC 3.4.6 is listed as a tested compiler for 1.47.0; is this warning then expected? Or not? The change that silences the compiler is declaring the destructor of boost::error_info_base to be virtual, but I'm not entirely sure if that's correct. I'm also hesitant to make this change only for CentOS 4 as that will change the object layout in memory and could result in linker confusion, though one could argue that linking against the wrong library is an error unto itself. If there's a more appropriate place to report/discuss these sorts of issues, please point me towards them. Thanks! -- Chris Cleeland

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Jamfile.v2 for iostreams in Boost 1_48
by David Smith 17 Jan '12

17 Jan '12

Greetings, The Jamfile.v2 in the iostreams library of Boost 1_48 has the line (around 29): $(v) = [ modules.peek : $(v) ] ; Used to propogate path-constant settings to the local jam environment. I think it should be: $($(v)) = [ modules.peek : $(v) ] ; At least when I run with this the build of iostreams works correctly to compile bzip2 and zlib objects and fails otherwise. Has anyone else observed this? Regards David

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boost::mpl, c++11 and clang 3.0: compiler bug?
by Allan Nielsen 17 Jan '12

17 Jan '12

Hi The following code compiles fine under clang 3.0 but I get unexpected output: #include <iostream> #include <boost/mpl/for_each.hpp> #include <boost/mpl/vector.hpp> template< typename _state > struct AccSize{ size_t s = 0; _state xxxx; template<typename T> void operator()(T) { std::cout << s << " " << sizeof(T) << std::endl; s += sizeof(T); }; }; struct Foo { Foo () {} Foo (const Foo & rhs) {} }; struct A{}; int main(int argc, const char *argv[]) { using namespace std; AccSize < Foo > p; typedef boost::mpl::vector<int, int, int> list; boost::mpl::for_each< list >( p ); return 0; } The output I get is: 0 4 0 4 0 4 The output I expected is: 0 4 4 4 8 4 If I remove the copy constructor in Foo, it works as I expect, and if I do a "normal" initialization of AccSize::s it also works as I expect. Is this a bug? If so, how can it be reproduced without mpl::foreach Best regards Allan W. Nielsen

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[interprocess] hanging when open_or_create a mapped file
by yiling1 gong 17 Jan '12

17 Jan '12

hello, everyone: I’m a newbie to boost::interprocess, It’s really a cool library, so I try to write a simple program to test mapped file, it’s really simple: #include <boost/interprocess/managed_mapped_file.hpp> using namespace boost::interprocess; int main() { managed_mapped_file mfile(open_or_create, "/home/fractal/log.bin", 1024); //hanging here. return 0; } but it’s hanging on the creation of mapped file, I test it both on ubuntu 11.05(in virtualbox) and openSuse, the same problem remain. I’m sure the file exists, and I traced down the source code, it seems the program stuck in a while loop in function priv_open_or_create(...). except that, if I set the third argument of constructor from 1024 to 1, it’s even throw a exception( not good). any seggestion is appreciated!!!

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boost::interprocess::detail::managed_open_or_create_impl::priv_open_or_create function
by Raghu Gyambavantha 16 Jan '12

16 Jan '12

Boost-ers, When I try to allocate more elements from a managed shared memory segment than allowed, I don't seem to be getting an error from the boost library. It looks like the reason for it is because the call to "construct_func" from "priv_open_or_create" in "boost::interprocess::detail::managed_open_or_create_impl" returns true/false, but that return value is never checked. I saw this error with boost versrion 1.43.0, but that specific portion of the code doesn't seem to have changed even in 1.48.0. >From the looks of it, it seems like the construct_func should throw instead of returning, but in 1.43.0, it is returning a value. Should the return value be check and appropriate action be taken here or am I missing something. Any help is much appreciated. Thanks, -Raghu

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