August 2010 - Boost-users - lists.preview.boost.org

[DateTime] from time_t to ptime and back - or not
by Christoph Duelli 23 Aug '10

23 Aug '10

[I am using Boost 1.43.0 on linux, gcc 4.4.1] I am having trouble with date_time's ptime. I am passing it a time_t, and store that in a ptime object. When I retrieve the time_t, I am getting a different value than the one I passed to it originally. (the difference seems to be 2 hours - in all probability due to UTC vs local time issues). Code: time_t now = time(NULL); boost::posix_time::ptime pt = boost::posix_time::from_time_t(now); struct tm tm = to_tm(pt); time_t should_be_now = mktime(&tm); BOOST_CHECK_EQUAL(now, should_be_now); fails for me: now is by 7200 seconds (i.e. 2 hours) ahead of. Is this a bug in date_time or am I just failing to use it properly? Thank you, and best regards Christoph

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[bind]Help! Can we modify parameters before pass them into bind (see the context below for details)
by jungleman 23 Aug '10

23 Aug '10

Hi, I have some problems on function template bind. the original usage of bind is : bind(func, _1, _2), and I wonder whether I can modify the parameters before pass them into bind, for example, functype function = bind(func, *_1, *_2). So that, when I use function(a, b), it will do like this: func(*a, *b). May it work, or some way else to do this? I just wanna do this in one line code. thanks in advance. -- Stay hungry, stay foolish !

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Boost.Intrusive issues on IBM compiler
by Jeremiah Willcock 22 Aug '10

22 Aug '10

It appears that almost all of the Boost.Intrusive tests (at <URL:http://tinyurl.com/2bzhglh>, for example) fail on IBM's compiler. I get similar results, like the following from the test suite, from my own code: An expression of type "overloaded function: U::to_node_ptr" cannot be converted to type "boost::intrusive::list_node<void *> *(boost::intrusive::detail::base_hook_traits<boost::intrusive::testvalue<hooks<void *>,0>,boost::intrusive::list_node_traits<void *>,1,boost::intrusive::default_tag,1>::*)(testvalue<hooks<void *>,0> &)" Is there an easy workaround for this issue? Is there a plan to fix it? This has also been reported a couple of months ago as bug 4412 (<URL:https://svn.boost.org/trac/boost/ticket/4412>). Thank you. -- Jeremiah Willcock

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axpy_prod Weirdness
by Jane Shevtsov 22 Aug '10

22 Aug '10

I have a little program that implements an ecological network analysis algorithm. (It looks at the importance of indirect energy or matter flows between species.) 01 //dea.cpp -- The fundamental DEA algorithm 02 03 #include <boost/numeric/ublas/matrix.hpp> 04 #include <boost/numeric/ublas/operation.hpp> 05 #include <boost/numeric/ublas/io.hpp> //for test 06 #include "storage_adaptors.hpp" //for test 07 08 using boost::numeric::ublas::matrix; 09 10 void dea(const matrix<double>[], int, int, matrix<double>[]); 11 matrix<double> indflow(const matrix<double> & Ndea, const matrix<double> & Gdea); 12 13 int main() { 14 using boost::numeric::ublas::make_matrix_from_pointer; 15 matrix<double> Garr[4]; 16 matrix<double> Narr[2]; 17 double G1[3][3] = {0, 0, 0, 0.33333, 0, 0, 0.66667, 1, 0}; 18 double G2[3][3] = {0, 0, 0, 0.6, 0, 0, 0.4, 1, 0}; 19 double G3[3][3] = {0, 0, 0, 0.55, 0, 0, 0.45, 1, 0}; 20 double G4[3][3] = {0, 0, 0, 0.5, 0, 0, 0.5, 1, 0}; 21 Garr[0] = make_matrix_from_pointer(G1); 22 Garr[1] = make_matrix_from_pointer(G2); 23 Garr[2] = make_matrix_from_pointer(G3); 24 Garr[3] = make_matrix_from_pointer(G4); 25 dea(Garr, 2, 4, Narr); 26 std::cout << Narr[0] << std::endl; 27 matrix<double> ratio = indflow(Narr[0], Garr[0]); 28 std::cout << ratio << std::endl; 29 return 0; 30 } 31 32 //The fundamental DEA algorithm 33 //Takes array of G matrices, window size, array length and empty array for N_DEA matrices as input 34 void dea(const matrix<double> Garr[], int win, int arrLen, matrix<double> Narr[]) { 35 using namespace boost::numeric::ublas; 36 int matSize = Garr[0].size1(); 37 for (int i = 0; i < arrLen - win; i++) { 38 matrix<double> Gprod = identity_matrix<double>(matSize); 39 Narr[i] = identity_matrix<double>(matSize); 40 //the core loop 41 for (int j = 0; j < win; j++) { 42 Gprod = prod(Gprod, Garr[i+j]); 43 Narr[i] += Gprod; 44 } 45 } 46 } 47 48 //computes indirect flow fraction 49 matrix<double> indflow(const matrix<double> & Ndea, const matrix<double> & Gdea) { 50 using namespace boost::numeric::ublas; 51 int matSize = Ndea.size1(); 52 matrix<double> iflow = Ndea - Gdea - identity_matrix<double>(matSize); //Ind = N-G-I 53 matrix<double> frac = zero_matrix<double>(matSize, matSize); //inialize indirect flow fraction matrix 54 //perform division for nonzero, off-diagonal elements 55 for (int i=0; i<matSize; i++) { 56 for (int j=0; j<matSize; j++) { 57 if (i != j && Ndea(i,j) != 0) //avoid division by zero 58 frac(i, j) = iflow(i, j) / Ndea(i, j); 59 } 60 } 61 return frac; 62 } The correct output is below. [3,3]((1,0,0),(0.33333,1,0),(1.26667,1,1)) [3,3]((0,0,0),(0,0,0),(0.473683,0,0)) The code given above works, but to speed it up, I tried replacing the first line of the core loop in dea() with axpy_prod(Gprod, Garr[i+j], Gprod, true);. This gives the following wrong output: [3,3]((1,0,0),(0,1,0),(0,0,1)) [3,3]((0,0,0),(0,0,0),(0,0,0)) And if I use axpy_prod(Gprod, Garr[i+j], Gprod, false);, I get: [3,3]((3,0,0),(1.26666,3,0),(2.33334,3,3)) [3,3]((0,0,0),(0.736843,0,0),(0.714285,0.666667,0)) What gives? When should I avoid using axpy_prod? -- ------------- Jane Shevtsov Ecology Ph.D. candidate, University of Georgia co-founder, <www.worldbeyondborders.org> Check out my blog, <http://perceivingwholes.blogspot.com>Perceiving Wholes "The whole person must have both the humility to nurture the Earth and the pride to go to Mars." --Wyn Wachhorst, The Dream of Spaceflight

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[bind]Help! Can we modify parameters before pass them into bind (see the context below for details)
by jungleman 22 Aug '10

22 Aug '10

Hi, I have some problems on function template bind. when I uses stl algorithm adjacent_find(inputIterator begin, inputIterator) -- Stay hungry, stay foolish !

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[asio] Feature request for serializable types.
by Germán Diago 22 Aug '10

22 Aug '10

Hello. I'm using boost.asio and trying to serialize a boost.variant, which is serializable because each of the fields I used in the variant have a serialize method required by boost.serialization library. I want to send my variant as binary data. This is not easy although I have a serialize method because this does not work: async_write(mysocket, boost::asio::buffer(myserializablevariant), when_done); I think all serializable types should be automatically usable as boost::asio::buffer, like std::vector, in this call. I think this shouldn't be too hard to implement, but I don't know how to serialize my data in binary format in a straight-forward way. Any ideas? Thanks in advance.

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thread-safe initialization for singleton
by Kraus Philipp 22 Aug '10

22 Aug '10

Hi, I have written a class with static methods and properties. Now the class must be used in a multithreaded environment, so I get some race conditions error. I use boost::thread for implementating the threads. I have found boost_once but I don't know how to use it, so my class properties are initialized once. Thanks Phil

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multiple serialized objects to same file
by Oscar Pernas 21 Aug '10

21 Aug '10

Hi! I know that this question is asked before but I cant see any answer about it. Is posible with boost serialization to write different objects to the same file? if is possible, is possible to access to each object with an iterator or with position like binary files? thanks -- Óscar Pernas Plaza.

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[BGL] segFault
by John Robertson 21 Aug '10

21 Aug '10

I'm trying to obtain an iterator of edges with a different ordering than that given in egdes(g). The following compiles but segfaults at std::sort( VE.begin(), VE.end(), ordering< Graph, edd >() ); (runs ok if the above line is commented out) //////////////////////////////////////////////////////////////////////////////////////////////////////////////// typedef Traits::edge_descriptor edd; // Create ordering template < typename Graph, typename edd > struct ordering { Graph & g; bool operator ()(const edd & a, const edd & b) { return g[a].eName < g[b].eName; } }; template < typename Graph > int initialize_container( Graph & g ) { typename graph_traits<Graph>::edge_iterator edge_iter, edges_end; // create vector of edge descriptors. std::vector< Traits::edge_descriptor > VE(num_edges(g)+1); int i = 1; // (Sometimes I like to start at 1.) //insert edge descriptors into vector of edge descriptors. for (tie(edge_iter, edges_end) = edges(g); edge_iter != edges_end; ++edge_iter) { cout << " *edge_iter = " << *edge_iter << endl; VE[i++] = *edge_iter; } // segfaults here //sort vector of edge descriptors. std::sort( VE.begin(), VE.end(), ordering< Graph, edd >() ); //print sorted edge descriptors. for( int i = 1; i < num_edges(g)+1; ++i ) cout << " -Edge " << i << " = " << VE[i] << endl; } Thanks

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[BGL] Updating the source vertex of an edge in-place
by Daniel Trebbien 21 Aug '10

21 Aug '10

I need to be able to update the source vertex of an edge in-place. The only option that I see is to remove the edge with `remove_edge` and then add a new edge with `add_edge`. The problem, however, is that I think this will mess up a property map of an edge property if it cannot expand to map a new value for the newly-added edge. Thus, I would like to update the edge in-place. How do I do this?

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[propertytree] more beginners questions
by Dietmar Hummel 21 Aug '10

21 Aug '10

Hi! I have some more questions regarding property tree (for parsing xml) and maybe someone could help me. Lets assume we have the following xml file to read: <a> <b> <c><d>1</d></c> <c><d>2</d></c> <c><d>3</d></c> <x></x> </b> </a> Now, my idea was to parse all the c-nodes by calling a specific function for each of them. Something like this... void parseDNode( const boost::property_tree::ptree& v ) { //... } void parseCNode( const boost::property_tree::ptree::value_type& v ) { parseDNode( v.second.get_child( "d" ) ); } void load( const std::string& filename ) { boost::property_tree::ptree pt; boost::property_tree::read_xml(filename, pt); BOOST_FOREACH( boost::property_tree::ptree::value_type &v, pt.get_child( "a.b.c" ) ) { parseCNode( v ); } } ---- Now I have several questions for this: 1. The code doesn't work as expected, it just handles the first one of the c nodes 2. The function parseCNode() also doesn't work. I assumed that v is a reference to the c node where I have to claim the d-node by get_child. But it seems v is already pointing to d? 3. I don't understand why BOOST_FOREACH is working with value_type here. As far as I see, get_child returns a self_type which should be a ptree? See also the different parameter lists for parseCNode and parseDNode... Thanks in advance.... Regards Dietmar

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MPICH2 + Boost.MPI Collective Problems
by Stephan Hackstedt 21 Aug '10

21 Aug '10

Hi there, i have a big problem by running MPI programs which use the Boost.MPI library. When i'm trying to run programs on *more *than one node, collective operations like communicator::barrier<http://boost.org/doc/libs/1_44_0/doc/html/boost/mpi/communicator.html#id918…>or broadcast,<http://boost.org/doc/libs/1_44_0/doc/html/boost/mpi/broadcast.html>or even the environment<http://boost.org/doc/libs/1_44_0/doc/html/boost/mpi/environment.html>destructor (cause of FINALIZE, which is colletive) causing the programm to crash. I got errors like this : *[1]terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::mpi::exception> >' [1] what(): MPI_Barrier: Other MPI error, error stack: [1]PMPI_Barrier(362).................: MPI_Barrier(MPI_COMM_WORLD) failed [1]MPIR_Barrier_impl(255)............: [1]MPIR_Barrier_intra(79)............: [1]MPIC_Sendrecv(186)................: [1]MPIC_Wait(534)....................: [1]MPIDI_CH3I_Progress(184)..........: [1]MPID_nem_mpich2_blocking_recv(895): [1]MPID_nem_tcp_connpoll(1746).......: Communication error with rank 0: * I also tested this with the simple broadcast example from the Boost.MPI tutorial - same errors.. But when using the original MPI equivalent without the Boost.MPI library, such as MPI_Barrier<http://www.mpi-forum.org/docs/mpi-11-html/node66.html#Node66>, the programm runs well. I am using MPICH2 on Ubuntu 10.04 platforms. Someone had problems like this or know a fix for that? Regards, stephan

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Using unordered_set or unordered_map to hold small array(s) of ints
by B Hart 21 Aug '10

21 Aug '10

Can someone please provide an example of how to best use unordered_map/set to store/lookup many small arrays of integers. e.g. unsigned int I[5] = {1000,3344455,12455222,8832232}; I'm guessing that there is no facility for using raw C++ arrays, and that one must wrap them in a struct. Thanks in advance.

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Beginner question: Why boost::signal creates another instance of the slot object ?
by Mauricio Gomes 20 Aug '10

20 Aug '10

Hi, I am running the program below (Vista with boost 1.43, mingw/gcc 4.5.1). I would expect slot.x to be 5 but it is zero. Why boost::signal creates another instance of the slot object ? What am I missing here ? Thank you in advance for your attention, Mau. ---------------------------------------------------------------- #include <iostream> #include <boost/signal.hpp> struct S { int x; S (): x(0) {} void operator () (int i) { std::cout << "&slot1 = " << this << std::endl; x = i; std::cout << "slot1.x = " << this->x << std::endl; } }; int main () { S slot; boost::signal<void (int)> sig; std::cout << "&slot2 = " << &slot << std::endl; sig.connect (slot); sig (5); std::cout << "slot2.x = " << slot.x << std::endl; return 0; } -------------------------------------------------------------------- Output: &slot2 = 0x22fee4 &slot1 = 0x341448 slot1.x = 5 slot2.x = 0

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How to best use unordered_set or unordered_map to hold small array(s) of ints
by B Hart 20 Aug '10

20 Aug '10

I posted this last night, but not sure it went through to the list as I don't see it in my sent items and I never got any responses. Sorry if it is duplicate. I'm hoping someone could offer an example or advice on how to best use unordered_set or unordered_map to hold many small arrays of unsigned integers. I would like to use the built in hash function rather than have to create one. Also, since I have many of these small arrays, keeping the memory footprint small and the hash time at a minimum are important concerns. A typical int array would hold 5 unsigned ints. Maybe someone could offer example code or suggestions. The samples I see are always the trivial case of just entering a single number or string as key or value. Thanks.

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[property tree] silly beginners question
by Dietmar Hummel 20 Aug '10

20 Aug '10

Hi all! I am trying to read an xml file with property tree (first try). Because I have dots int the tag names I must use the extended version of the get functions. So here is the slightly modified example code, which sadly does'nt compile on vc2008. Probably its a totally silly error on my side... // Loads debug_settings structure from the specified XML file void load(const std::string &filename) { // Create an empty property tree object using boost::property_tree::ptree; ptree pt; // Load the XML file into the property tree. If reading fails // (cannot open file, parse error), an exception is thrown. read_xml(filename, pt); // Get the filename and store it in the m_file variable. // Note that we construct the path to the value by separating // the individual keys with dots. If dots appear in the keys, // a path type with a different separator can be used. // If the debug.filename key is not found, an exception is thrown. std::string m_file = pt.get< std::string >( '/', "debug/filename" ); // Get the debug level and store it in the m_level variable. // This is another version of the get method: if the value is // not found, the default value (specified by the second // parameter) is returned instead. The type of the value // extracted is determined by the type of the second parameter, // so we can simply write get(...) instead of get<int>(...). int m_level = pt.get( '/', "debug/level", 0); // Iterate over the debug.modules section and store all found // modules in the m_modules set. The get_child() function // returns a reference to the child at the specified path; if // there is no such child, it throws. Property tree iterators // are models of BidirectionalIterator. std::vector< std::string > m_modules; BOOST_FOREACH( ptree::value_type &v, pt.get_child( '/', "debug/modules" ) ) { m_modules.push_back( v.second.data() ); } } vc says: 1>c:\projekte\proptreetest\proptreetest\proptreetest.cpp(23) : error C2664: 'std::basic_string<_Elem,_Traits,_Ax> boost::property_tree::basic_ptree<Key,Data>::get<std::string>(const boost::property_tree::string_path<String,Translator> &,const Type &) const': Konvertierung des Parameters 1 von 'char' in 'const boost::property_tree::string_path<String,Translator> &' nicht möglich 1> with 1> [ 1> _Elem=char, 1> _Traits=std::char_traits<char>, 1> _Ax=std::allocator<char>, 1> Key=std::string, 1> Data=std::string, 1> String=std::string, 1> Translator=boost::property_tree::id_translator<std::string>, 1> Type=std::string 1> ] 1> and 1> [ 1> String=std::string, 1> Translator=boost::property_tree::id_translator<std::string> 1> ] So, it looks to me like the compiler does'nt know about the extended get functions... Regards Dietmar

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[Log] How to use?
by Olivier Tournaire 20 Aug '10

20 Aug '10

Hi all, i am currently trying to use Boost.Log in my application. After fighting the two last days, I still do not understand how to correctly use the lib. I would like the result to be the same as the one provided by the example advanced_use.cpp. So, I wrote a simple class to make some tests. As I want to use the logging library in a shared library (an application plugin), I made a simple test: compile the class which uses Log in a shared library and link an executable against this library. I also have created an executable which directly compiles the class (so does not link against the shared library). Basically, I have a test_boost_log class. The constructor is a copy/paste of the code from the example advanced_use.cpp: #include "test_boost_log.hpp" #include <cassert> #include <iostream> #include <fstream> #include <boost/shared_ptr.hpp> #include <boost/log/common.hpp> #include <boost/log/filters.hpp> #include <boost/log/formatters.hpp> #include <boost/log/attributes.hpp> #include <boost/log/sinks.hpp> #include <boost/log/utility/empty_deleter.hpp> #include <boost/log/utility/scoped_attribute.hpp> namespace logging = boost::log; namespace fmt = boost::log::formatters; namespace flt = boost::log::filters; namespace sinks = boost::log::sinks; namespace attrs = boost::log::attributes; namespace src = boost::log::sources; namespace keywords = boost::log::keywords; using boost::shared_ptr; // Here we define our application severity levels. enum severity_level { normal, notification, warning, error, critical }; // The formatting logic for the severity level template< typename CharT, typename TraitsT > inline std::basic_ostream< CharT, TraitsT >& operator<< ( std::basic_ostream< CharT, TraitsT >& strm, severity_level lvl) { static const char* const str[] = { "normal", "notification", "warning", "error", "critical" }; if (static_cast< std::size_t >(lvl) < (sizeof(str) / sizeof(*str))) strm << str[lvl]; else strm << static_cast< int >(lvl); return strm; } int foo(src::logger& lg) { BOOST_LOG_FUNCTION(); BOOST_LOG(lg) << "foo is being called"; return 10; } test_boost_log::test_boost_log() { // For now we only create a text output sink: typedef sinks::synchronous_sink< sinks::text_ostream_backend > text_sink; shared_ptr< text_sink > pSink(new text_sink); { text_sink::locked_backend_ptr pBackend = pSink->locked_backend(); shared_ptr< std::ostream > pStream(&std::clog, logging::empty_deleter()); pBackend->add_stream(pStream); shared_ptr< std::ofstream > pStream2(new std::ofstream("sample.log")); assert(pStream2->is_open()); pBackend->add_stream(pStream2); } logging::core::get()->add_sink(pSink); src::logger lg; BOOST_LOG(lg) << "Hello, World!"; pSink->locked_backend()->set_formatter(fmt::stream << fmt::attr("LineID") // First an attribute "LineID" is written to the log << " [" << fmt::date_time< boost::posix_time::ptime >("TimeStamp", "%d.%m.%Y %H:%M:%S.%f") << "] [" << fmt::attr< severity_level >("Severity", std::nothrow) << "] [" << fmt::time_duration< boost::posix_time::time_duration >("Uptime") << "] [" // then this delimiter separates it from the rest of the line << fmt::if_(flt::has_attr("Tag")) [ fmt::stream << fmt::attr< std::string >("Tag") << "] [" // yet another delimiter ] << fmt::named_scope("Scope", keywords::iteration = fmt::reverse) << "] " << fmt::message()); // here goes the log record text shared_ptr< logging::attribute > pCounter(new attrs::counter< unsigned int >(1)); // Since we intend to count all logging records ever made by the application, // this attribute should clearly be global. logging::core::get()->add_global_attribute("LineID", pCounter); // And similarly add a time stamp shared_ptr< logging::attribute > pTimeStamp(new attrs::local_clock()); logging::core::get()->add_global_attribute("TimeStamp", pTimeStamp); // And an up time stopwatch BOOST_LOG_SCOPED_THREAD_ATTR("Uptime", attrs::timer); // Let's also track the execution scope from which the records are made boost::shared_ptr< logging::attribute > pNamedScope(new attrs::named_scope()); logging::core::get()->add_thread_attribute("Scope", pNamedScope); // We can mark the current execution scope now - it's the 'main' function BOOST_LOG_FUNCTION(); // Let's try out the counter attribute and formatting BOOST_LOG(lg) << "Some log line with a counter"; BOOST_LOG(lg) << "Another log line with the counter"; { BOOST_LOG_NAMED_SCOPE("Tagging scope"); // Now these lines will be highlighted with the tag BOOST_LOG(lg) << "Some tagged log line"; BOOST_LOG(lg) << "Another tagged log line"; } // And this line is not highlighted anymore BOOST_LOG(lg) << "Now the tag is removed"; pSink->set_filter( flt::attr< severity_level >("Severity", std::nothrow) >= warning // Write all records with "warning" severity or higher || flt::attr< std::string >("Tag", std::nothrow).begins_with("IMPORTANT")); // ...or specifically tagged src::severity_logger< severity_level > slg; // These two lines test filtering based on severity BOOST_LOG_SEV(slg, normal) << "A normal severity message, will not pass to the output"; BOOST_LOG_SEV(slg, error) << "An error severity message, will pass to the output"; { // Next we try if the second condition of the filter works // We mark following lines with a tag BOOST_LOG_SCOPED_THREAD_TAG("Tag", std::string, "IMPORTANT MESSAGES"); BOOST_LOG(slg) << "Some really urgent line"; } pSink->reset_filter(); // And moreover, it is possible to nest logging records. For example, this will // be processed in the order of evaluation: BOOST_LOG(lg) << "The result of foo is " << foo(lg); } I have added another method to test the logger state: void test_boost_log::a_test_method_to_see_if_the_logger_is_still_working() { src::severity_logger< severity_level > slg; BOOST_LOG_SEV(slg, error) << "An error severity message, will pass to the output"; } My main: #include "test_boost_log.hpp" int main(int argc, char** argv) { test_boost_log tbl; tbl.a_test_method_to_see_if_the_logger_is_still_working(); return 0; } Here is the output of the program: Hello, World! 1 [17.08.2010 21:22:43.083302] [] [00:00:00.000076] [test_boost_log::test_boost_log()] Some log line with a counter 2 [17.08.2010 21:22:43.083445] [] [00:00:00.000217] [test_boost_log::test_boost_log()] Another log line with the counter 3 [17.08.2010 21:22:43.083484] [] [00:00:00.000256] [Tagged line] [Tagging scope<-test_boost_log::test_boost_log()] Some tagged log line 4 [17.08.2010 21:22:43.083517] [] [00:00:00.000289] [Tagged line] [Tagging scope<-test_boost_log::test_boost_log()] Another tagged log line 5 [17.08.2010 21:22:43.083556] [] [00:00:00.000328] [test_boost_log::test_boost_log()] Now the tag is removed 6 [17.08.2010 21:22:43.083598] [error] [00:00:00.000370] [test_boost_log::test_boost_log()] An error severity message, will pass to the output 7 [17.08.2010 21:22:43.083633] [normal] [00:00:00.000405] [IMPORTANT MESSAGES] [test_boost_log::test_boost_log()] Some really urgent line 9 [17.08.2010 21:22:43.083673] [] [00:00:00.000444] [int foo(boost::log_mt_posix::sources::logger&)<-test_boost_log::test_boost_log()] foo is being called 8 [17.08.2010 21:22:43.083668] [] [00:00:00.000440] [test_boost_log::test_boost_log()] The result of foo is 10 *terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::log_mt_posix::missing_value> >'* * what(): Requested attribute value not found* So, the logger throws, sample.log is created, but empty. The library and the executable are compiled with -DBOOST_LOG_USE_CHAR and -DBOOST_LOG_DYN_LINK If someone could help... Best regards, Olivier PS: boost_1.42, log_1.0 (from sourceforge), g++4.3.4, 64bits ubuntu

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A question about "prim_minimum_spanning_tree.hpp"
by 王伟 20 Aug '10

20 Aug '10

Hi, I'm studying MST algorithms in GPU recently.I need BGL implementation as coparison,But I have a problem in using prim_minimum_spanning_tree.hpp.The problem is:when I use large input(e.g. >1M),there's a "segmnetation error" problem.But when the input(e.g. 1K) is small,the result is noproblem. I haven't found know the reason yet.My complier is gcc 4.1.2,OS is RHEL5. Help would be appreciated. Thanks in advance. Wang wei The complete code is in the attachment.

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Some trouble using mutexes
by Ernest Galbrun 20 Aug '10

20 Aug '10

Dear boost users, I would be really grateful if someone could give me a hint about what I am doing wrong with the mutex and thread class (I am using boost 1.43, on windows XP running visual c++ 2010, the library has been built using the bjam utility). I have a main thread that creates an object of class robot : class Robot { private: boost::mutex tcpLock; boost::thread continuousThread; ... } Robot k3; this thread launches a thread that makes continuous calls to a member function of the robot. Since this function uses network ressources, I want it to be safe so i use a lock The function called is the only function in my program that uses this lock : int Robot::sendMsg(string msg, int n, vector<string>* answer) { tcpLock.lock(); (do stuff with the tcp io service) tcpLock.unlock(); return 0; } Of course, I also call this function from the main thread. And I have disruptive behavior, which I don't understand. When debugging, I see that the 'active_count' of the tcpLock object stays negative or ==0, which seem absolutely wrong to me, but I don't understand how it could ever be anything other than 0 or 1. Any clue, advice, web link, or soft injures are welcome ! -- Ernest Galbrun

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ptree info format - block commenting
by Hite, Christopher 20 Aug '10

20 Aug '10

http://www.boost.org/doc/libs/1_41_0/doc/html/boost_propertytree/parsers .html#boost_propertytree.parsers.info_parser I'm using the ptree info format. How about C-style commenting out of a block of config stuff like? /* Stuff I { don't need } */ Chris

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[Interprocess] "You cannot bind an lvalue to an rvalue reference" in 1.44 using VC10
by Phil Ratzloff 20 Aug '10

20 Aug '10

When I attempt to compile a project using boost::interprocess I get compile errors when I include managed_mapped_file.hpp when using VC10. I can create a simple project that is just the following code: #include <boost\interprocess\managed_mapped_file.hpp> int main(int argc, char* argv[]) { return 0; } When compiling, I get the following errors: Empty.cpp c:\lib\boost_1_44_0\boost\interprocess\detail\move.hpp(342): error C2440: 'return' : cannot convert from 'boost::interprocess::mapped_region' to 'boost::interprocess::mapped_region &&' You cannot bind an lvalue to an rvalue reference c:\lib\boost_1_44_0\boost\interprocess\mapped_region.hpp(159) : see reference to function template instantiation 'boost::interprocess::mapped_region &&boost::interprocess::move<boost::interprocess::mapped_region&>(T)' being compiled with [ T=boost::interprocess::mapped_region & ] c:\lib\boost_1_44_0\boost\interprocess\detail\move.hpp(342): error C2440: 'return' : cannot convert from 'boost::interprocess::detail::file_wrapper' to 'boost::interprocess::detail::file_wrapper &&' You cannot bind an lvalue to an rvalue reference c:\lib\boost_1_44_0\boost\interprocess\detail\file_wrapper.hpp(63) : see reference to function template instantiation 'boost::interprocess::detail::file_wrapper &&boost::interprocess::move<boost::interprocess::detail::file_wrapper&>(T)' being compiled with [ T=boost::interprocess::detail::file_wrapper & ] c:\lib\boost_1_44_0\boost\interprocess\detail\move.hpp(342): error C2440: 'return' : cannot convert from 'boost::interprocess::file_mapping' to 'boost::interprocess::file_mapping &&' You cannot bind an lvalue to an rvalue reference c:\lib\boost_1_44_0\boost\interprocess\file_mapping.hpp(62) : see reference to function template instantiation 'boost::interprocess::file_mapping &&boost::interprocess::move<boost::interprocess::file_mapping&>(T)' being compiled with [ T=boost::interprocess::file_mapping & ] When I look at move.hpp(342) I find the following code: #if defined(BOOST_MOVE_DOXYGEN_INVOKED) ...unused code... #else template <class T> inline typename remove_reference<T>::type&& move(T&& t) { return t; } #endif It is complaining about the "return t;" statement. I have just moved up from boost 1.43, where I have been working without problems with VC10. Is there something I should be doing to prevent this, or is it a bug?

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[log] calling init_from_stream() or init_from_settings() more than once (reinitialize at runtime)
by Oskar Nordquist 19 Aug '10

19 Aug '10

Hello, I've just started experimenting with the unofficial Boost.Log by Andrey Semashev. I would like to know the defined behaviour of calling init_from_stream() and init_from_settings() more than once, i.e. is it possible to re-initialize with new settings at run time? Basically I would like to do this: boost::log::settings setts; setts["Sink:File"]["Filter"] = "%Severity% > 4"; setts["Sink:File"]["Destination"] = "TextFile"; setts["Sink:File"]["FileName"] = "MyApp_%3N.log"; setts["Sink:File"]["AutoFlush"] = true; setts["Sink:File"]["RotationSize"] = 10 * 1024 * 1024; // 10 MiB boost::log::init_from_settings(setts); // ... later on change severity filter to >= 0 setts["Sink:File"]["Filter"] = "%Severity% >= 0"; boost::log::init_from_settings(setts); This does not work. It seems I am able to add new sinks without problem, but modifying existing sinks is not possible. I think that being able to reinitialize at runtime is an absolutely vital feature. Being able to change a settings file and then just reinit to turn on logging! Please tell me this is already supported and I am doing something wrong, or at least that this will be supported in the future :) Regards, Oskar

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[mpl] Reconstructing an mpl::list from mpl::l_item's.
by AJG 19 Aug '10

19 Aug '10

Hi there, Using mpl::remove, et al. I can eliminate types from an mpl::list. However, it appears that the result is not an actual mpl::list, but some sort of indexed, cons-like structure composed of mpl::l_item types. Is there a way to recreate an mpl::list proper using these l_item's? E.g. typedef mpl::list<foo, bar, qux> L; typedef mpl::remove<L, bar>::type R; typedef mpl::???<R>::type => mpl::list<foo, qux>; Thanks!

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filesystem lambda and for_each
by Jean-Christophe Roux 19 Aug '10

19 Aug '10

hello, Despite some research, I am struggling to combine boost filesystem, boost lambda and STL for_each. 32 std::string str = ""; 33 std::string path = "/tmp"; 34 boost::filesystem::directory_iterator it(path); 35 while(it != boost::filesystem::directory_iterator()) 36 { 37 str += it->path().filename() + "<br>"; 38 ++it; 39 } works fine but 40 std::for_each(boost::filesystem::directory_iterator(path), boost::filesystem::directory_iterator(), 41 str += *boost::lambda::_1.path().parent_path() ); does not compile with the error message that : error: ‘const struct boost::lambda::lambda_functor<boost::lambda::placeholder<1> >’ has no member named ‘path’ I don't understand why and I don't really see how I could have this work. Also, I am wondering why with _1 instead of boost::lambda::_1 I am getting: error: reference to ‘_1’ is ambiguous /usr/local/include/boost/lambda/core.hpp:69: thanks!

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Throwing an exception in a packaged_task: is there a clear example?
by Mark Wilson 19 Aug '10

19 Aug '10

Hello, I am throwing an exception from a packaged_task, and then trying to catch it with f.get() (where f is a unique_future); it doesn't work, the program just terminates with: terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::unknown_exception>' what(): std::exception Is there a simple example somewhere, or could someone provide one, that makes clear how this mechanism is supposed to work? The Threads documentation does not show how to do this... Here is my simple program, based on the example in the docs: #include <boost/thread.hpp> #include <boost/thread/future.hpp> #include <boost/exception/all.hpp> struct MyException { MyException() { } }; int calculate_the_answer_to_life_the_universe_and_everything() { throw MyException(); return 42; } int main() { boost::packaged_task<int> task(calculate_the_answer_to_life_the_universe_and_everything); boost::unique_future<int> f(task.get_future()); boost::thread t(boost::move(task)); try { f.get(); } catch(MyException& ex) { std::cout << "EXCEPTION!" << std::endl; } } Thanks, Mark Wilson

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