February 2021 - Boost-users - lists.preview.boost.org

Clarification on statechart post_event vs process_event within react()
by John McCabe 10 Jan '22

10 Jan '22

Hi, Apologies if this has already been answered/clarified, but my search of the internet to try to get a definitive answer, at least one I recognised as being definitive, was unsuccessful. Below I have posted some source code, based on the stopwatch example from the tutorial, but using an 'external' object to delegate the actual handling of event stuff to and using the state, rather than simple_state base class, and some other tweaks. This is a cut down version of something that someone I work with has devised, but I just wanted to get a clear answer on whether process_event() should be getting called in cases like this. I think it probably should not since, in the code below, you change state (with a state object's destructor being executed) whilst you're executing that state's react(EvStartStop) function. If someone can confirm this is the correct interpretation that would be very much appreciated. Any questions, feel free to ask (BTW - I'm compiling for C++17) John PS - In case it's of any use, the output from running this code is: ------ Entered Active Entered Stopped Stopped - payload2 m_charValue: a Exited ~Stopped <<<--- This is the bit I don't like the look of because... Entered Running Active - payload2 m_charValue: a <<<--- ... this happens from the forward_event() call payload1 value1: 20 payload1 value2: 200.2 Exited ~Running Entered Stopped Exiting Program Exited ~Stopped Exited ~Active ------ If I swap the //*** comments to the doProcess() lines instead of doPost(), the output seems more sensible ------ Entered Active Entered Stopped Stopped - payload2 m_charValue: a Exited ~Stopped Entered Running Active - payload2 m_charValue: a payload1 value1: 20 payload1 value2: 200.2 Exited ~Running Entered Stopped Exiting Program Exited ~Stopped Exited ~Active ------ ========== code =========== #include <boost/statechart/event.hpp> #include <boost/statechart/state_machine.hpp> #include <boost/statechart/state.hpp> #include <boost/statechart/transition.hpp> #include <boost/statechart/custom_reaction.hpp> #include <boost/mpl/list.hpp> #include <iostream> #include <string> namespace sc = boost::statechart; namespace mpl = boost::mpl; // Forward declare a handler 'class' that's going to have activity delegated to it struct Handler; // Normal example start/stop and reset events struct EvStartStop : sc::event<EvStartStop> {}; struct EvReset : sc::event<EvReset> {}; // A couple of events that carry data with them struct EvPayload1 : sc::event<EvPayload1> { EvPayload1(int value1, double value2) : m_value1 { value1 }, m_value2 { value2 } {}; int m_value1 { 0 }; double m_value2 { 0.0 }; }; struct EvPayload2 : sc::event<EvPayload2> { EvPayload2(const char& charValue) : m_charValue { charValue } {}; char m_charValue { false }; }; // Back to the example bits struct Active; struct StopWatch : sc::state_machine<StopWatch, Active> { typedef sc::transition<EvReset, Active> reactions; // The extra 'handler' stuff void setHandler(Handler* handler) { m_handler = handler; }; Handler* getHandler() const { return m_handler; }; Handler* m_handler { nullptr }; // Used to make post_event() accessible from an external class...seems unpleasant, but... using sc::state_machine<StopWatch, Active>::post_event; }; // The implementation of the Handler class; created with a reference to a StopWatch object struct Handler { Handler(StopWatch& stopWatch) : m_stopWatch { stopWatch } {}; void doPost() { m_stopWatch.post_event(EvStartStop()); } void doProcess() { m_stopWatch.process_event(EvStartStop()); } StopWatch& m_stopWatch; }; struct Stopped; struct Active : sc::state<Active, StopWatch, Stopped> { Active(my_context ctx) : my_base { ctx } { std::cout << "Entered Active" << std::endl; }; ~Active() { std::cout << "Exited ~Active" << std::endl; }; typedef mpl::list<sc::custom_reaction<EvPayload1>, sc::custom_reaction<EvPayload2>, sc::transition<EvReset, Active>> reactions; sc::result react(const EvPayload1& payload1) { std::cout << "payload1 Event NOT HANDLED" << std::endl; return discard_event(); } sc::result react(const EvPayload2& payload2) { std::cout << "Active - payload2 m_charValue: " << payload2.m_charValue << std::endl; return discard_event(); } }; struct Running : sc::state<Running, Active> { Running(my_context ctx) : my_base { ctx } { std::cout << "Entered Running" << std::endl; }; ~Running() { std::cout << "Exited ~Running" << std::endl; }; typedef mpl::list<sc::custom_reaction<EvPayload1>, sc::transition<EvStartStop, Stopped>> reactions; sc::result react(const EvPayload1& payload1) { std::cout << "payload1 value1: " << payload1.m_value1 << std::endl; std::cout << "payload1 value2: " << payload1.m_value2 << std::endl; //***context<StopWatch>().getHandler()->doPost(); context<StopWatch>().getHandler()->doProcess(); return discard_event(); } }; struct Stopped : sc::state<Stopped, Active> { Stopped(my_context ctx) : my_base { ctx } { std::cout << "Entered Stopped" << std::endl; }; ~Stopped() { std::cout << "Exited ~Stopped" << std::endl; }; typedef mpl::list<sc::custom_reaction<EvPayload2>, sc::transition<EvStartStop, Running>> reactions; sc::result react(const EvPayload2& payload2) { std::cout << "Stopped - payload2 m_charValue: " << payload2.m_charValue << std::endl; //***context<StopWatch>().getHandler()->doPost(); context<StopWatch>().getHandler()->doProcess(); return forward_event(); } }; int main() { StopWatch myWatch; Handler myHandler(myWatch); myWatch.setHandler(&myHandler); myWatch.initiate(); myWatch.process_event(EvPayload2 { 'a' }); myWatch.process_event(EvPayload1 { 20, 200.2 }); std::cout << "Exiting Program" << std::endl; return 0; }

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CMake's PCH support and boost.test linker error
by Olaf Peter 04 Mar '21

04 Mar '21

Hello Boost users I have here a strange problem which occurs only if I try to build with precompiled headers using CMake. I've configured the project for use with dynamically linking. The error is: /usr/bin/ld: /usr/lib/gcc/x86_64-redhat-linux/10/../../../../lib64/crt1.o: in function `_start': (.text+0x24): undefined reference to `main' Something obvious? Thanks in advance The project's reduce is: ---8<--- test_driver.cpp --- 8< ---- #defineBOOST_TEST_MODULE "My Test Suite" #include<boost/test/unit_test.hpp> --->8------>8------>8--- ---8<--- test_x.cpp --- 8< ---- #include<boost/test/unit_test.hpp> .... --->8------>8------>8--- ---8<--- src/CMakeLists.txt --- 8< ---- ... set_source_files_properties(src/test_xxx.cpp APPEND PROPERTIES COMPILE_DEFINITIONS "BOOST_TEST_DYN_LINK" ) .... --->8------>8------>8------>8------>8------>8--- ---8<--- pch.pp --- 8< ---- #pragma once #include<boost/test/unit_test.hpp> --->8------>8------>8---

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[boost::units] Best practices for implementing custom units and quantities
by Alexandru Onea 01 Mar '21

01 Mar '21

Hello community, I am working on a project which works with units such as scale intervals (cents, moria, etc.) depending on the temperament system used (24-EDO, 72-EDO, etc.). My implementation defines a namespace for each tuning system. Within the namespaces I define base units, units and a system, as well as conversion factors between the systems. The base dimension is defined in only one of the namespaces (corresponding to the tuning system which I consider "standard" which is the 1200 cents per octave system). 1. Does such an approach qualify as a good approach in general (leaving aside the musical aspects)? 2. Is it a good practice to place all these namespaces in boost::units (extend boost::units)? Or should I keep them within my own namespaces? Learning the answer to #2 is more interesting to me, even in the absence of an answer to #1. Best regards, Alexandru Onea

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Question about Boost Integer
by Emilio Paolini 28 Feb '21

28 Feb '21

Hi everyone, i'm pretty new to Boost. I need to use as a default type for the CNL. The problem is that i would need an integer type that can assume only 2^4 values (so basically that stays on 4 bits). What i am asking is that if there is a way to define an integer like int128_t but instead of 128 i would need to have 4. Thank you very much for your answers. Emilio

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flyweights, nested flyweights and shared libraries
by Andreas Buykx 25 Feb '21

25 Feb '21

I want to use boost::flyweight to capture some structures containing const data. The documentation states that if flyweights are exported across shared library boundaries that the intermodule holder should be used. Since my flyweights are all created in the same shared library I would prefer to use the static holder but I keep getting crashes. I tried the intermodule holder but I'm having trouble compiling my sources with that. So my thinking was to wrap all flyweight types in accessor classes which are exposed instead, and the accessor classes create the flyweights within the same shared library to store the data. Would that be a valid approach? Also, is it possible to have nested flyweights (when they are wrapped by accessor classes)? And would that cause any additional problems in the above scenario? Below is an example of what I'm trying to achieve... Thanks for your advice! Andreas === Foo.h === struct FooDetails { FooDetails( std::string text_, std::vector<double> values ); std::string text; std::vector<double> values; }; class STUFF_EXPORT Foo { public: Foo( std::string text_, std::vector<double> values ); // rule-of-5 constructors declared, and default-implemented in cpp file const std::string& text() const; const std::vector<double>& values() const; private: boost::flyweight<FooDetails> m_data; }; === Foo.cpp === FooDetails( ( std::string text_, std::vector<double> values_ ) : text(text_), values( values_ ) { } Foo::Foo( std::string text_, std::vector<double> values_ ) m_data( FooDetails( text_, values_ ) ) { } std::string Foo::text() const { return m_data.get().text; } std::vector<double> Foo::values() const { return m_data.get().values; } === Bar.h === struct BarDetails { BarDetails( Foo foo_, std::vector<long> ids_ ); Foo foo; //< Foo holds a flyweight std::vector<long> ids; }; class STUFF_EXPORT Bar { public: Bar( std::string text_, std::vector<double> values_, std::vector<long> ids_ ); // rule-of-5 constructors declared, and default-implemented in cpp file const std::string& text() const; const std::vector<double>& values() const; const std::vector<long>& ids() const; private: boost::flyweight<BarDetails> m_bar; }; === Bar.cpp === BarDetails::BarDetails( Foo foo_, std::vector<long> ids_ ) : foo( foo_ ), ids( ids_ ) { } Bar::Bar( std::string text_, std::vector<double> values_, std::vector<long> ids_ ) : m_bar( Foo( text_, values), ids_ ) { } const std::string& Bar::text() const { return m_bar.get().m_foo.text(); } const std::vector<double>& Bar::values() const { return m_bar.get().foo.values(); } const std::vector<long>& Bar::ids() const { return m_bar.get().ids; }

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Re: [Boost-users] Boost-users Digest, Vol 5456, Issue 1
by philippe DALET 23 Feb '21

23 Feb '21

Hi, I have built some binaries for boost and python https://sourceforge.net/projects/pcpu/files/Boost/ boost 1.71 python3.7&numpy3.7 for ubuntu 20.04 64 bits boost 1.75 python3.789&numpy3.789 for visual studio 2019 mscv14.2 - win10 Ph.DALET Le mar. 23 févr. 2021 à 11:03, <boost-users-request(a)lists.boost.org> a écrit : > Send Boost-users mailing list submissions to > boost-users(a)lists.boost.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://lists.boost.org/mailman/listinfo.cgi/boost-users > or, via email, send a message with subject or body 'help' to > boost-users-request(a)lists.boost.org > > You can reach the person managing the list at > boost-users-owner(a)lists.boost.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Boost-users digest..." > > > Today's Topics: > > 1. Re: Boost cannot find numpy37 on Dockerized Ubuntu 20.04 > (Roy de Bokx) > 2. Re: flyweights, nested flyweights and shared libraries > (Andreas Buykx) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Mon, 22 Feb 2021 15:49:11 +0100 > From: Roy de Bokx <rdebokx1990(a)gmail.com> > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] Boost cannot find numpy37 on Dockerized > Ubuntu 20.04 > Message-ID: > < > CAFLoxwXy8_an1jZh_PQMkjppbOWyixvR5Exw1DCeaUyV9xDfBA(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Op vr 19 feb. 2021 om 22:05 schreef Nathan Ernst via Boost-users < > boost-users(a)lists.boost.org>: > > > The missing symbols you quoted come from python itself. It looks like > > you're missing a "-lpython" linker flag. > > > Thanks! That definitely put me on the right track. Eventually I got it > working using the "-lpython3.6m" flag, since I found that the Python3.6 .so > file was situated at /usr/lib/x86_64-linux-gnu/libpython3.6m.so > Many thanks, this is much appreciated! I've pasted the full Dockerfile in > https://github.com/boostorg/boost/issues/462, in case anyone is > interested. > > > > > Regards, > > Nathan > > > > On Fri, Feb 19, 2021, 4:47 AM Roy de Bokx via Boost-users < > > boost-users(a)lists.boost.org> wrote: > > > >> > >> > >> Op wo 17 feb. 2021 om 20:30 schreef Anonymous Maarten < > >> anonymous.maarten(a)gmail.com>: > >> > >>> Thanks for your answer Maarten! > >>>> Please bare with me as I'm a little new to this. Is there some way I > >>>> can change the interpreter that is used for installing boost? Or do > you > >>>> think that adapting the --prefix flag may also work? > >>>> > >>> > >>> When using the pre-built boost packages of a linux distribution > >>> (ubuntu), you're generally stuck with the versions/options that its > >>> packagers have chosen. > >>> A distribution freezes versions to make a more robust experience. > >>> > >>> Adding a `--prefix` will not help because, first of all, it's not a > >>> valid gcc option, and second, ubuntu 18.04 does not provide a > >>> libboost-python-py37 shared/static library. > >>> Do you really need python 3.7? Doesn't 3.6 suffice? > >>> > >> > >> Thanks! This helped me understanding the issue a bit further. I think > 3.6 > >> should suffice indeed, so I tried using 3.6 by removing the 3.7 > >> installation from the Dockerfile and using the -lboost_numpy3 flag > instead. > >> It seems I ran into some linking issue after this. It was able to find > >> the right numpy3.so and libboost_python3-py36.so, but I'm getting a lot > of > >> errors like these: > >> > >> //usr/lib/x86_64-linux-gnu/libboost_numpy3.so: undefined reference to > >> `PyExc_ValueError' > >> > >> //usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1: undefined > >> reference to `PyLong_AsLong' > >> > >> //usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1: undefined > >> reference to `PyNumber_InPlaceFloorDivide' > >> > >> //usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1: undefined > >> reference to `PyBool_Type' > >> etc... > >> > >> I've pasted the full docker file and logs in > >> https://github.com/boostorg/boost/issues/462 > >> Thanks again for any help. > >> > >>> > >>> If you really want to use Boost.Python + python 3.7, you can do 2 > things: > >>> - stay on ubuntu bionic and build boost yourself (or use an alternative > >>> c/c++ package manager, e.g. [conan](https://conan.io/) has a [boost > >>> package](https://conan.io/center/boost)) > >>> - more to a more recent ubuntu release. e.g. ubuntu 20.10 has python > >>> 3.8: > >>> > https://packages.ubuntu.com/groovy/amd64/libboost-python1.71-dev/filelist > >>> > >> I've also given 20.10 a try, however I ran into the same linking issues > >> as mentioned above. > >> > >>> > >>> > >>> > >>> _______________________________________________ > >> Boost-users mailing list > >> Boost-users(a)lists.boost.org > >> https://lists.boost.org/mailman/listinfo.cgi/boost-users > >> > > _______________________________________________ > > Boost-users mailing list > > Boost-users(a)lists.boost.org > > https://lists.boost.org/mailman/listinfo.cgi/boost-users > > >

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Re: [Boost-users] Boost cannot find numpy37 on Dockerized Ubuntu 20.04
by Roy de Bokx 22 Feb '21

22 Feb '21

Op wo 17 feb. 2021 om 20:30 schreef Anonymous Maarten < anonymous.maarten(a)gmail.com>: > Thanks for your answer Maarten! >> Please bare with me as I'm a little new to this. Is there some way I can >> change the interpreter that is used for installing boost? Or do you think >> that adapting the --prefix flag may also work? >> > > When using the pre-built boost packages of a linux distribution (ubuntu), > you're generally stuck with the versions/options that its packagers have > chosen. > A distribution freezes versions to make a more robust experience. > > Adding a `--prefix` will not help because, first of all, it's not a valid > gcc option, and second, ubuntu 18.04 does not provide a > libboost-python-py37 shared/static library. > Do you really need python 3.7? Doesn't 3.6 suffice? > Thanks! This helped me understanding the issue a bit further. I think 3.6 should suffice indeed, so I tried using 3.6 by removing the 3.7 installation from the Dockerfile and using the -lboost_numpy3 flag instead. It seems I ran into some linking issue after this. It was able to find the right numpy3.so and libboost_python3-py36.so, but I'm getting a lot of errors like these: //usr/lib/x86_64-linux-gnu/libboost_numpy3.so: undefined reference to `PyExc_ValueError' //usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1: undefined reference to `PyLong_AsLong' //usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1: undefined reference to `PyNumber_InPlaceFloorDivide' //usr/lib/x86_64-linux-gnu/libboost_python3-py36.so.1.65.1: undefined reference to `PyBool_Type' etc... I've pasted the full docker file and logs in https://github.com/boostorg/boost/issues/462 Thanks again for any help. > > If you really want to use Boost.Python + python 3.7, you can do 2 things: > - stay on ubuntu bionic and build boost yourself (or use an alternative > c/c++ package manager, e.g. [conan](https://conan.io/) has a [boost > package](https://conan.io/center/boost)) > - more to a more recent ubuntu release. e.g. ubuntu 20.10 has python 3.8: > https://packages.ubuntu.com/groovy/amd64/libboost-python1.71-dev/filelist > I've also given 20.10 a try, however I ran into the same linking issues as mentioned above. > > > >

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Prooblem building software with fstream.hpp
by Mack Wallace 21 Feb '21

21 Feb '21

Hi all. I'm a noob and unfamiliar with boost. It has also been a long time since I have done any C++ programming. In any case, here are the details: I am trying to compile MecnRao/TCP-UDP-Proxy that uses the Boost Library. I am trying to compile this for Windows, ultimately Windows 10, but at the moment trying to compile on my Windows 7 VM. I am using Visual Studio Pro 2019. After trying the latest version of the Boost Library with some errors due to some deprecated members, I bounced around older versions until finding that Version 1.68.0 reduced my compile errors substantially, and of those 20 or so errors, are caused by some typedef problems in fstream.hpp. (I could be wrong, but the errors all seem to be related to fstream_fix.) Specifically, I get the following errors to begin with: 'fstream_fix<std::basic_ifstream<char,std::char_traits<char> > >' is not a variable template 'fstream_fix<std::basic_ofstream<char,std::char_traits<char> > >' is not a variable template This comes from the following lines in the fstream.hpp typedef basic_ifstream<char> ifstream; typedef basic_ofstream<char> ofstream; Where ifstream and ofstream are indicated as being redefined as #define ifstream fstream_fix<std::ifstream> #define ofstream fstream_fix<std::ofstream> Within the program with fstream_fix as template<class T> struct fstream_fix : public T { fstream_fix(){}; template<class T1> fstream_fix(T1 v1){ setlocale(LC_CTYPE, ""); T::open(v1); setlocale(LC_CTYPE, 0); } template<class T1,class T2> fstream_fix(T1 v1,T2 v2){ setlocale(LC_CTYPE, ""); T::open(v1,v2); setlocale(LC_CTYPE, 0); } template<class T1> void open(T1 v1){ setlocale(LC_CTYPE, ""); T::open(v1); setlocale(LC_CTYPE, 0); } template<class T1,class T2> void open(T1 v1,T2 v2){ setlocale(LC_CTYPE, ""); T::open(v1,v2); setlocale(LC_CTYPE, 0); } }; So I'm wondering if this is a newer/different compiler issue? Or the application itself? Or maybe just missing something like uses namespace std. I am hoping someone can help me nip this last problem so I can get this compiled. Thanks, Mack

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boost::asio::read() gets stuck when there's no internet
by Child OfGod 20 Feb '21

20 Feb '21

In TgBot library i use under MSVC++, in tgbot/net/BoostHttpOnlySslClient.cpp, a call to boost::asio::read() does not return when internet is disconnected for a few minutes. I would appreciate any help to get this resolved, i.e. for the read function to return if it fails after some timeout has passed the code block in the tgbot/net/BoostHttpOnlySslClient.cpp file: [code] string BoostHttpOnlySslClient::makeRequest(const Url& url, const vector<HttpReqArg>& args) const { tcp::resolver resolver(_ioService); tcp::resolver::query query(url.host, "443"); ssl::context context(ssl::context::tlsv12_client); context.set_default_verify_paths(); ssl::stream<tcp::socket> socket(_ioService, context); connect(socket.lowest_layer(), resolver.resolve(query)); #ifdef TGBOT_DISABLE_NAGLES_ALGORITHM socket.lowest_layer().set_option(tcp::no_delay(true)); #endif //TGBOT_DISABLE_NAGLES_ALGORITHM #ifdef TGBOT_CHANGE_SOCKET_BUFFER_SIZE #if _arm64 || _WIN64 || __amd64__ || __x86_64__ || __MINGW64__ || __aarch64__ || __powerpc64__ socket.lowest_layer().set_option(socket_base::send_buffer_size(65536)); socket.lowest_layer().set_option(socket_base::receive_buffer_size(65536)); #else //for 32-bit socket.lowest_layer().set_option(socket_base::send_buffer_size(32768)); socket.lowest_layer().set_option(socket_base::receive_buffer_size(32768)); #endif //Processor architecture #endif //TGBOT_CHANGE_SOCKET_BUFFER_SIZE socket.set_verify_mode(ssl::verify_none); socket.set_verify_callback(ssl::rfc2818_verification(url.host)); socket.handshake(ssl::stream<tcp::socket>::client); string requestText = _httpParser.generateRequest(url, args, false); write(socket, buffer(requestText.c_str(), requestText.length())); string response; #ifdef TGBOT_CHANGE_READ_BUFFER_SIZE #if _M_ARM64 || _WIN64 || __amd64__ || __x86_64__ || __MINGW64__ || __aarch64__ || __powerpc64__ char buff[65536]; #else //for 32-bit char buff[32768]; #endif //Processor architecture #else char buff[1024]; #endif //TGBOT_CHANGE_READ_BUFFER_SIZE boost::system::error_code error; while (!error) { std::size_t bytes = read(socket, buffer(buff), error); response += string(buff, bytes); } return _httpParser.extractBody(response); } [/code] Thankyou in advance😀🙏

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(no subject)
by Dk Jack 18 Feb '21

18 Feb '21

Hi, I am using boost 1.58 in my project. Ran into a crash in the boost filesystem library. I've included the relevant stack trace at the end of the email. My code is something like this: boost::filesystem::path fpath(mFilename.c_str()); if (!boost::filesystem::exists(fpath)) { // log a message and return. return; } auto curr_time = boost::filesystem::last_write_time(fpath); <== crash The crash is not consistent and happened randomly. I tested the above code in a small test program with just the above code. I made the input file unreadable etc, even then it was able to successfully read the last write timestamp of the file without any issues. Not sure why this particular call would throw an error. Since it's compiled with -O2, the error code is optimized out in the stack trace. Any ideas? Thanks for your help. Dk. (gdb) bt #0 0x00007f01651ba387 in raise () from /lib64/libc.so.6 #1 0x00007f01651bba78 in abort () from /lib64/libc.so.6 #2 0x00007f0160d087d5 in __gnu_cxx::__verbose_terminate_handler() () from /lib64/libstdc++.so.6 #3 0x00007f0160d06746 in ?? () from /lib64/libstdc++.so.6 #4 0x00007f0160d06773 in std::terminate() () from /lib64/libstdc++.so.6 #5 0x00007f0160d06993 in __cxa_throw () from /lib64/libstdc++.so.6 #6 0x00007f0161171f5f in boost::filesystem::detail::last_write_time(boost::filesystem::path const&, boost::system::error_code*) () from xxx.so #7 0x00007f0161089657 in last_write_time (p=...) at /usr/local/include/boost/filesystem/operations.hpp:594

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