March 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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Tried to unzip a file , and followed the example in the boost.org as well, but it doesn't work
by asfskfdjkj kfasjfkasjf 03 Apr '21

03 Apr '21

Hi guys I tried to unzip a file with code below which exactly like the example from boost.org, but it doesn't work the example is in the link which is Zlib Filters | | | | Zlib Filters | | | I tried the code like the below try{ ifstream file("d:\\202012303333629003180526491.txt.zip", ios_base::in | ios_base::binary); boost::iostreams::filtering_streambuf<boost::iostreams::input> in; in.push(boost::iostreams::zlib_decompressor()); in.push(file); boost::iostreams::copy(in, cout); return 0;}catch (const std::exception& error) { std::cerr << error.what() << std::endl; return (EXIT_FAILURE); } it's not working, it get exception when it excuted boost::iostreams::copy(in, cout); I got the zlib error: iostream stream error exception thoughwhat wrong I have done though? thank you

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[Spirit] [Fusion] Concise way to construct attribute object
by Phil Endecott 28 Mar '21

28 Mar '21

Dear Experts, I currently have something like: struct S { string name; string value; }; BOOST_FUSION_ADAPT_STRUCT( S, name, value ) using S_rule = qi::rule<ITER, skipper, S()>; S_rule r %= identifier >> lit(':') >> identifier; Note that I can use %= here and I don't need to write an explicit semantic action to assign to S. Now say I modify S: class S { public: S(string name_, string value_); // May be default-constructable, copyable, assignable etc. // - but name and value are not individually assignable. }; Question: what is the best way to use that with the qi parser rule? I was hoping to find something in Fusion that would allow me to adapt the new class so that it can be used with %= as before, but I don't see anything appropriate. Currently the best that I can think of is: S_rule r = ( identifier >> lit(':') >> identifier ) [ _val = boost::phoenix::construct<S>(_1,_2) ]; How can I improve on that? Thanks, Phil.

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[Core] scoped_enum and template arguments
by Alan Barr 24 Mar '21

24 Mar '21

Hi, I'm a little confused about the following statement in the docs for scoped enum: > The emulated scoped enum can not be used in switch nor in > template arguments. https://www.boost.org/doc/libs/1_75_0/libs/core/doc/html/core/scoped_enum.h… I understand the rationale for the switch statement part (and indeed it won't compile in C++03). However, I'm struggling to grasp the template argument part (and I'll be the first to admit I'm not particularly strong with templates). Unlike the switch case, any basic scenario I've thrown at it compiles. So I'm not sure if this is a case of "should not" vs "can not". When would using a "scoped_enum_type" in a template argument as opposed to "BOOST_SCOPED_ENUM_NATIVE(scoped_enum_type)" become a problem? Or, why should I use "boost::optional<BOOST_SCOPED_ENUM_NATIVE(future_errc)>" over "boost::optional<future_errc>" ? I've got a compiler explorer link with some test code here if it helps: https://godbolt.org/z/dfr6M6vrW Regards, Alan

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Boost 64bit in Embarcadero C++ Builder
by Michael Morelli 17 Mar '21

17 Mar '21

Hi folks, we are testing the Boost.Test-Framework (installed with GetIt-Package Boost). We use C++ Builder 10.4.1 with Boost 1.70.0. We have created a new C++ Console-Application (with VCL enabled). Under Project->Options we have set '_TCHAR as char', because Boost.Test seems to need this mapping. It is not working with ' _TCHAR as wchar_t' The application main-entry-function is imported via #include <boost/test/included/unit_test.hpp>. The application then is run with the params : --log_level=all --report_level=detailed --build_info=true The console-output seems to be fuzzy : 1. Why is the platform win32? We use target-platform win64 and have installed boost 64bit via getit... 2. Paths are outputted with '\' and '/' 3. The fatal-error is correct but the consoleoutput 'St9exception' seems not correctly interpreted (charset ?) Are we doing something wrong or do you have some tipps regarding this ? Thx a lot. This is the console-output : [cid:image001.png@01D71B23.032439B0] Kind regards, Michael Morelli

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[release] Boost 1.76.0 beta 1 released
by Marshall Clow 16 Mar '21

16 Mar '21

Boost release 1.76.0 beta 1 is now available at: <https://dl.bintray.com/boostorg/beta/1.76.0.beta1/source/> The SHA256 checksums are as follows: 39eecd9672e78b95c8e3fdec1430a63788d528a66d3c8799c4639238e5d785bd boost_1_76_0_b1.7z c32edd34f767dd4bb67b86f76ebf58cf76822a5993a9b434c028b2dd08cfeefc boost_1_76_0_b1.zip 3ec1f92fa0a159b7073e39dd88f527a55d1f35e8986a3c560f202a75bdb8d584 boost_1_76_0_b1.tar.gz eb098d6d5352e10b17a3c49d2927ed61f09b6544f7c534627de35dfa2560fe20 boost_1_76_0_b1.tar.bz2 For details of what's in the release, see <https://www.boost.org/users/history/version_1_76_0.html>. Please download the beta, give it a try, and report any problems you encounter. Thanks, -- The Boost Release Team

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[release] Boost 1.76.0 Beta 1 Release Candidate 2
by Marshall Clow 13 Mar '21

13 Mar '21

The second release candidates for the 1.76.0 beta release are now available at: <https://dl.bintray.com/boostorg/beta/1.76.0.beta1/source/> The SHA256 checksums are as follows: c32edd34f767dd4bb67b86f76ebf58cf76822a5993a9b434c028b2dd08cfeefc boost_1_76_0_b1_rc2.zip eb098d6d5352e10b17a3c49d2927ed61f09b6544f7c534627de35dfa2560fe20 boost_1_76_0_b1_rc2.tar.bz2 39eecd9672e78b95c8e3fdec1430a63788d528a66d3c8799c4639238e5d785bd boost_1_76_0_b1_rc2.7z 3ec1f92fa0a159b7073e39dd88f527a55d1f35e8986a3c560f202a75bdb8d584 boost_1_76_0_b1_rc2.tar.gz The only changes from RC1 is an update to Boost.Interprocess, which was failing to compile on Mac OS X. As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. -- The Release managers

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[release] Boost 1.76.0 Beta 1 Release Candidate 1
by Marshall Clow 11 Mar '21

11 Mar '21

The first release candidates for the 1.76.0 beta release are now available at: <https://dl.bintray.com/boostorg/beta/1.76.0.beta1/source/> The SHA256 checksums are as follows: a222d325cd3c9f66951ec9026eca6ff6f48dd563c9a025911d598d2aca8770ce boost_1_76_0_b1_rc1.tar.bz2 6b90b510a3de38fc30a071ac798da37545fb60a1d6b21aed1130b47c9c598977 boost_1_76_0_b1_rc1.zip b01627bd9ce934b092037da81696bb4482a44e6a31c8791dbed82eafe04b69fa boost_1_76_0_b1_rc1.tar.gz dbef57adbab1d4395d14000f0a2420fc82f87476e10d48359ceff7125a74b77a boost_1_76_0_b1_rc1.7z As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. -- The Release managers

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(no subject)
by Jinlong Shen 11 Mar '21

11 Mar '21

Dear Madam/Sir, I used the boost::statechart asynchronous_state_machine to create a simple state machine. The state machine, the events and states are regular classes and are not class templates. Everything builds and works well on linux and qnx platform. However, on windows I got message that the the initial state is undefined. I think I have dealt with forward declaration well since it is build on linux and qnx. On Windows microsoft this compiler is used: Microsoft (R) C/C++ Optimizing Compiler Version 19.00.24215.1 for x64 The error message is like this. (ClCompile target) -> C:\Program Files\boost_1_64_0\boost/statechart/state_machine.hpp(701): error C2027: use of undefined type 'xxxx::FirstState' C:\Program Files\boost_1_64_0\boost/statechart/state_machine.hpp(701): error C3861: 'initial_deep_construct': identifier not found Any hint how it could be wrong with Microsoft C++? Best regards,Jinlong Shen

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Boost accepted in Google Summer of Code 2021
by David Bellot 09 Mar '21

09 Mar '21

We're in again! https://github.com/boostorg/wiki/wiki/Google-Summer-of-Code%3A-2021 David

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MSM and multithreading. Not clear what pattern to follow.
by Andrea Fiorito 08 Mar '21

08 Mar '21

Hi, I'm trying to use MSM to implement a client server component for my app. The client is broadcasting a msg, that servers in a local network will detect and respond. The client at that point will connect to one of the servers and interact following the network protocol. For the network and threading I'm using boost ASIO. I have 2 submachines that manage one the discovering part, and the other the connection and dialogue with one server part. I found that would be beneficial to run the submachines in one thread managed by an io_context, with the idea of stopping that context to cancel all the asynchronous operations. Unfortunately there are some weird behaviours with submachines, and not getting if I missed the right way of doing things or else. the description of my last stopper is here: https://github.com/boostorg/msm/issues/37 Is anyone able to point me on the right direction? Regards, Andrea

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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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How should a "using zlib ..." jam statement look, for Boost to link to ZLib in the form of SO filename (libz.so) instead of by -lz?
by Bob 03 Mar '21

03 Mar '21

Hello Boost mailing list, I am building a code project in my user home directory on OpenBSD, and doing this involves both a local build of Boost and also a local build of ZLib. I do the whole build using GCC. This is a relatively ordinary build use case, however GCC on OpenBSD (at least in its current version) has a peculiarity to it, which is that it adds to LD the argument "-L/usr/lib" in the leading position, and this means that LD's search for libz.so will find and use the operating system's bundled ZLib binary which is /usr/lib/libz.so ALWAYS, and NEVER use my local libz.so . Can you help me understand if Boost can be customized to link to ZLib in the following way: I can force GCC/LD to use a particular libz.so file, by specifying it by filename, e.g. "gcc ... libz.so ...", "gcc ... /my/dir/libz.so ...", instead of by the conventional "-lz". Boost's build process is hardwired to "-lz" and I ask you to help me understand if there is a way to circumvent that. ZLIB_LIBRARY_PATH will not make "-lz" hit anything else than /usr/lib/libz.so , per the compiler's default -L/usr/lib in leading position, so it will not be of help to solve my problem. To my best awareness ZLIB_INCLUDE has nothing to do with linking, so it will not be of help to solve my problem. ZLIB_NAME would only be to customize the library name would it e.g. to "-lmycustomz", or what is it for? Please clarify so I could figure if it could be of help, though ideally i keep my local ZLib having its default name "libz.so". And this brings me to the path of solving the problem that I imagine could work, but that I don't understand fully from the Boost documentation: There is the possibility to customize ZLib build settings through the JAM configuration, that is user-config.jam . The syntax used is "using zlib ...". Can you please help me understand if this route works, if so how would that "using zlib ..." statement look, such that Boost's build process will NOT build ZLib itself, and then will NOT link to it via "-lz", but will instead link to it by "$MYCUSTOMBUILDDIR/libz.so"?

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Boost.Python + `RecursionError` during deallocation
by Andrew Jones 01 Mar '21

01 Mar '21

Hi, I just raised the following issue on the Python issue tracker: https://bugs.python.org/issue43351 But I'm sharing it here to widen the net ... Basically, when moving from Python 2.7.14 to Python 3.7.5, and when using Boost.Python (Boost version 1.6.9), I'm seeing a crash in finalisation due to: ``` Exception ignored in: <Boost.Python.life_support object at 0x2acf473c5d10> RecursionError: maximum recursion depth exceeded while calling a Python object Fatal Python error: Cannot recover from stack overflow. ``` Everything else with the Python that's running, and the Boost.Python interface, is consistent between 2.7.14 and 3.7.5 -- it is just the Python version that's changing. I should say, Python 3.7.5 does otherwise seem operable, it just falls over when running this certain code (which just walks a linked-list of ~1400 elements via Boost.Python). Has anyone seen anything like this before? Does this list feel this is more likely a Python-proper issue, or a Boost.Python issue? Cheers, Andrew

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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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