October 2011 - Boost-users - lists.preview.boost.org

[Review] Boost.Atomic review period extended
by Tim Blechmann 24 Oct '11

24 Oct '11

Hi all, Since there has been only rather limited discussion about the Boost.Atomic library and only one full review, the review period will be extended until next Sunday, October 30th. I encourage everyone with an interest in this library to participate in the remaining days of the review. If someone wants to do a review, but won't find the time during the review period, please let me know how much time you need. Cheers, Tim Review Manager

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[serialization] how can load the nth element using binary_archive?
by gongyiling 24 Oct '11

24 Oct '11

Hello, Everyone: boost::serialization is a cool library. I use it in my project. I encounter a problem now. I serialized a array of objects to file as following: std::ofstream ofs(filename, std::ios_base::binary); boost::binary_oarchive oar(ofs); oar << obj[0] << obj[1] << ... << obj[n-1]; Now I want to load the obj[i] (i>=0 && i<n) from file. I tried recording obj[i]'s position in file, then set file stream's pointer to that position and trying to load it, but failed with exception input_stream_error, can I by any means doing that? here is my minimun code segments: struct word_block { std::string word; template<typename Archive> void serialize(Archive & ar, const unsigned int file_version ) { ar & word; } }; int main(int argc, char* argv[]) { const char* filename = "words.idx"; word_block wb1, wb2, wb2_r; std::ofstream ofs(filename, std::ios_base::binary); boost::archive::binary_oarchive oar(ofs); oar << wb1; size_t wb2_pos = ofs.tellp(); //record the position of wb2. oar << wb2; ofs.close(); std::ifstream ifs(filename, std::ios_base::binary); boost::archive::binary_iarchive iar(ifs); ifs.seekg(wb2_pos); //set file pointer to wb2. iar >> wb2_r; //failed with exception input_stream_error. return 0; } Any idea is appreciated!

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ublas speed and multi-core processors
by petros 23 Oct '11

23 Oct '11

Hi, Is there any way to use ublas taking advantage of the multi-core facility of current processors? Even naive “strategies”, like breaking the number of rows of a targeted matrix expression across different threads would improve performance significantly, even if not optimally. It would be nice to be able to use the matrix expression templates to perform operations in a multi-threaded way. Is there any provision for this? Thank you for your help, Petros

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ublas matrix_range resize
by petros 22 Oct '11

22 Oct '11

HI, I wanted to ask how I can resize a matrix_range object. I understand that is is a very light/disposable object but here is the problem I want to solve: I need to wrap some Lapack functions (Linear equation solvers) using ublas. The package I am using (mkl) asks for specific memory requirements that translate to having a –possibly- larger lda (basically the hosting matrix number of rows). So my way to address this was to contain a general matrix (ublas::matrix) and derive from a matrix_range which references it. Alas, I cannot resize! Is there a way? – Yes I could contain a pointer to the matrix_range and reconstruct, but this is rather silly. There should be a way to assign a matrix_range to an existing one, overwriting its contents. Thank you, in advance, for your help, Petros

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boost serialization- handle endianness
by ohad barta 22 Oct '11

22 Oct '11

Hi I am serializing my data in a one computer, transfer it to another computer and desirialize the data there,.Does the data can get messed because of the 2 endian option, or is boost lobrary take care of it automatically? If I do need to handle this myself, are there any functions/MACROS in the boost serialization library that will help me? Many Thanks Ohad Barta

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[iostreams] Apply a filter temporarily - base64_encoder
by Fernando Pelliccioni 21 Oct '11

21 Oct '11

Is there any way to apply a filter temporarily ? I want to do this... io::filtering_ostream out; out.push_back(file_sink("my_file.txt")); out << "Authentication: "; out.push_front ( base64_encoder() ); // pseudo-code... see *push_front* instead of *push* out << make_ntlm_auth_from_system(); // this have to be base64 encoded out.pop_front(); // removes the base64_encoder out << "......"; // *NO* base64 encoded I don't want to do this... io::filtering_ostream out; out.push(file_sink("my_file.txt")); out << "Authentication: "; out.pop(); out.push(base64_encoder()); out.push(file_sink("my_file.txt")); out << make_ntlm_auth_from_system(); out.pop(); out.pop(); out.push(file_sink("my_file.txt")); out << "......"; The function make_ntlm_auth_from_system() creates an object that is *OStreamable*. Any other suggestions are welcome. :) Thanks and regards, Fernando.

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[Boost.Units] Trouble with I/O and specific scaled units
by Michael J Iatauro 21 Oct '11

21 Oct '11

I have the following declarations (reduced from a much larger problem): typedef make_system<si::second_base_unit>::type system; typedef unit<time_dimension, system> second; BOOST_UNITS_STATIC_CONSTANT(seconds, second); typedef make_scaled_unit<second, scale<60, static_rational<1> > >::type minute; BOOST_UNITS_STATIC_CONSTANT(minutes, minute); Unfortunately, if I try this: quantity<minute, double> t = 33.3 * minutes; std::cout << t << std::endl; I get, ultimately, a pair of compile errors: io.hpp:392: error: ‘name’ is not a member of ‘boost::units::scale_list_dim<boost::units::scale<60l, boost::units::static_rational<1l, 1l> > >’ io.hpp:326: error: ‘symbol’ is not a member of ‘boost::units::scale_list_dim<boost::units::scale<60l, boost::units::static_rational<1l, 1l> > >’ I tried adding std::string name_string(const minute&) { return "min"; } std::string symbol_string(const minute&) { return "min"; } but that didn't change anything. Interestingly, if I change the scale from 60 to 10, it compiles and runs fine. What am I missing? Thanks! ~MJI ------------------ Michael J. Iatauro Software Engineer Dell | Services, Federal Government NASA Ames Research Center Office: 650-604-0662 Mail stop: 269-2 P.O. Box 1 Moffett Field, CA 94035-0001 www.dell.com/perotsystems

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Serializing the same Objekt several times
by Fabian Weiss 21 Oct '11

21 Oct '11

At the moment I am working with XML serialization of Boost. I am serializing my own classes which works well. But my objects are changing often, for example: class Modul { public: setValue(int); private: int Value; } Modul* M = new Modul(); Now I wanna serialize M every time Value changes, so that I can save a complete history of changes on M. But M is serialized only once, after that I get this in my XML, although Value has changed: <Modul class_id_reference="1" object_id_reference="_2"></Modul> This is unusable for my purpose, so how can I stop that kind of "linking" and serialize the Objekt every time completely?

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[locale] IOStream encoding conversions?
by Jookia 21 Oct '11

21 Oct '11

Currently I'm messing about with Boost.Locale, I'm intending to use it for my project, but I don't know how to do something along the lines of specifying the external encoding (usually the user's locale, en_US.UTF-8 in my case), and the internal coding of my program (UTF-16), to have input and output converted, possibly using a codecvt. A possible example would be translating UTF-16->POSIX UTF-8 paths, or UTF-8->Windows UTF-16 paths. I've read the examples and 'Using Boost.Locale' documentation, but I can't figure out how to do it. In fact, the closest to this is in the 'Character Set Conversions' documentation, where somehow a generator is the boost::locale::conv namespace, but that doesn't work with streams. I tried to pry open the test code only to not understand much. I've searched the web for solutions, but since there's only limited use and documentation of this, I'm starting to wonder if I'm using the right tool for the job.

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unit_test compile error under MSVC10
by Marc de Kamps 21 Oct '11

21 Oct '11

Hi, I'm trying to emulate the following example using Visual Studio 10. In one file I have: --------- #ifndef QW #define QW #ifdef WIN32 #define BOOST_ALL_DYN_LINK // Force boost to use shared libraries #endif #define BOOST_TEST_MAIN #include <boost/test/unit_test.hpp> #endif // include guard -------------- By itself this compiles and runs, correctly reporting that there is an empty test tree. In a second file, Test1.cpp , I have: ----------------- #include <boost/test/unit_test.hpp> #ifdef WIN32 #define BOOST_ALL_DYN_LINK // Force boost to use shared libraries #endif BOOST_AUTO_TEST_CASE(Test1) { BOOST_REQUIRE(true); } -------------------------- Compiling now leads to the error below(I use multithreaded debug ddl for the project). Is there anything obvious I'm doing wrong? Thx, Marc boost_unit_test_framework-vc100-mt-gd-1_47.lib(boost_unit_test_framework-vc100-mt-gd-1_47.dll) : error LNK2005: "public: static class boost::unit_test::unit_test_log_t & __cdecl boost::unit_test::singleton<class boost::unit_test::unit_test_log_t>::instance(void)" (?instance@?$singleton@Vunit_test_log_t@unit_test@boost@@@unit_test@boost@@SAAAVunit_test_log_t@23@XZ) already defined in Test1.obj 5

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