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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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