October 2020 - Boost-users - lists.stage.boost.cppalliance.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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Boost.Numeric.Interval: Please specify rounding control mechanism
by Bastien Commelongue 01 Dec '20

01 Dec '20

Hello, I am building an app for IOS (ARM) and I had this issue while compiling: *Boost.Numeric.Interval: Please specify rounding control mechanism.* C99 version should be used in this case but __USE_ISOC99 is not defined. Modifying the condition with this code (using __cplusplus) fixed the issue: *boost/numeric/interval/hw_rounding.hpp(36)* *#if defined(BOOST_NUMERIC_INTERVAL_NO_HARDWARE) && (defined(__USE_ISOC99) || defined(__MSL__) || (defined __cplusplus && __cplusplus >= 201103L))# include <boost/numeric/interval/detail/c99_rounding_control.hpp>#endif* Let me know if I missed something or if you plan to integrate this modification in a next version. Cheers, Bastien Commelongue

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Boost 1.74: Coroutines2 on MSVC 2019 / C++20
by Daniel Petrovic 29 Oct '20

29 Oct '20

Using Boost 1.74. By using coroutines 2 on MSVC 2019 (v16.7.7) with C++20 there is a compilation issue regarding result_of which is replaced by invoke_result in C++20. Is there already some patch for 1.74 or maybe work in progress for 1.75 regarding this issue ? Regards Daniel

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[Signals2] Deprecated header warning VS2017 Boost 1.74
by Peter Barker 27 Oct '20

27 Oct '20

Hi, Just upgraded to Boost 1.74 from Boost 1.71. I'm getting a warning: c:\releases\lib\boost\boost_1_74_0\include\boost\function_output_iterator.hpp(14): note: This header is deprecated. Use <boost/iterator/function_output_iterator.hpp> instead. from this MWE: #include <boost/signals2/signal.hpp> int main() { } I'll have to #define BOOST_ALLOW_DEPRECATED_HEADERS I guess, but I'm surprised Boost libraries are using deprecated Boost headers. Regards, Pete

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A Newbie Boost.Build with Variants Question
by Ryan Heniser 24 Oct '20

24 Oct '20

Hi, I am building Boost 1.61 (we need this old version for other libraries) for the first time at work with Boost.Build (b2). I have successfully built Boost (using b2) for gcc 4.8. If I want to add one or more variants (for example using gcc 6.3), where should I put the Boost header’s include directory? Should one go inside each variant or should just one go at the root directory containing the variant directories? Kind regards, Ryan

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[Newbie][Intrusive] - Beginners question
by Gaier, Bjoern 22 Oct '20

22 Oct '20

Hey everybody, I looked into the boost intrusive container and played around with it a bit. I tried the following code: struct animal : public boost::intrusive::list_base_hook<> { std::string name; int legs; animal(std::string n, int l) : name{std::move(n)}, legs{l} {} }; int main(int argc, char **argv) { std::vector<animal> test; boost::intrusive::list<animal> wuff; for(int n = 0; n < 5; n++) { test.push_back(animal("Katze", 4)); } for(int n = 0; n < 5; n++) { wuff.push_back(test[n]); } for(int n = 0; n < 15; n++) { wuff.push_back(test[n]); } for(auto elem : wuff) { printf("%s\n", elem.name.c_str()); } } This code does crash! I guess this is because "test" relocated the memory and therefor "wuff" lost its references. I would expect the same result if I would have a std::list with pointers to animal structures - this is why I wonder what the benefit of an intrusive container is compared to the same container with just pointers in it. Hope someone can explain me this! Thank you in advance and kind greetings Björn Als GmbH eingetragen im Handelsregister Bad Homburg v.d.H. HRB 9816, USt.ID-Nr. DE 114 165 789 Geschäftsführer: Dr. Hiroshi Nakamura, Dr. Robert Plank, Markus Bode, Heiko Lampert, Takashi Nagano, Junichi Tajika, Ergin Cansiz.

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Does boost promise/future support corroutines?
by David Frank 19 Oct '20

19 Oct '20

Hi, Does boost promise/future support coroutines? For example, the get call only block the running coroutine, instead of the whole thread? Thanks,David

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Boost.MSM: Problem with defered events
by Georg Gast 16 Oct '20

16 Oct '20

Dear Boost users, i am currently writing a driver for the ADS1256 chip with Boost.MSM. Yes, there are other drivers. I do this for training and fun. During the startup phase i need to defer the requests from the user as the SPI bus is not yet available. To model the behaviour the most correct, i tried to model it with MSM. In the transition table, i use the "Defer" action to defer these events. In my Idle state, after the startup phase, there is a transition with this defered event going to the "work" states. In the debugger i can see, that the defered_event_queue holds one defered event and it is of my type but it is not processed. I did use boost 1.67.0 (from debian buster ) and also 1.74.0 (self compiled) to test this. My program can be also compiled under Windows and VS2019 as i handled the hardware interfacing with a abstract class. It works under Windows and 1.74.0. With VS2017 and 1.67.0 it also does not work. Under Linux and gcc it always stops at the Idle state where i wait for the defered event. At the end is my transition table. Any ideas are welcome! Georg // clang-format off struct transition_table : mpl::vector< // +----------------+-------------------+----------------+---------------------------+----------------------+ // Region 0 // +----------------+-------------------+----------------+---------------------------+----------------------+ // Start Event Next Action Guard // +----------------+-------------------+----------------+---------------------------+----------------------+ Row < NotIntialized , ev_Init , WaitDRDYID , none , none >, Row < WaitDRDYID , ev_CheckFlags , ReadID , none , IsDrdy0 >, Row < ReadID , ev_CheckFlags , none , none , none >, Row < ReadID , Spi::Reply , ReadIDFailed , none , IsIDNotOk >, Row < ReadID , Spi::Reply , Idle , none , IsIDOk >, // during the startup phase these event must be defered Row < NotIntialized , ev_MultiStart , none , Defer , none >, Row < WaitDRDYID , ev_MultiStart , none , Defer , none >, Row < ReadID , ev_MultiStart , none , Defer , none >, // +----------------+-------------------+----------------+---------------------------+----------------------+ Row < Idle , ev_CheckFlags , none , none , none >, Row < Idle , ev_MultiStart , MConfigWaitDRDY, none , none >, // +----------------+-------------------+----------------+---------------------------+----------------------+ Row < MConfigWaitDRDY, ev_CheckFlags , MSwitchConfig , none , IsDrdy0 >, Row < MSwitchConfig , ev_CheckFlags , none , none , none >, Row < MSwitchConfig , Spi::Reply , MMuxWaitDRDY , none , IsECNotFailed >, Row < MMuxWaitDRDY , ev_CheckFlags , MSwitchMux , none , IsDrdy0 >, Row < MSwitchMux , ev_CheckFlags , none , none , none >, Row < MSwitchMux , Spi::Reply , MSync , none , IsECNotFailed >, Row < MSync , Spi::Reply , MDataWaitDRDY , none , IsECNotFailed >, Row < MDataWaitDRDY , ev_CheckFlags , MReadData , none , IsDrdy0 >, Row < MReadData , ev_CheckFlags , none , none , none >, Row < MReadData , Spi::Reply , Idle , WorkDone , IsWorkDone >, Row < MReadData , Spi::Reply , MMuxWaitDRDY , RemoveDoneWork , IsStillWorkTodo >, // +----------------+-------------------+----------------+---------------------------+----------------------+ // Region 1 // +----------------+-------------------+----------------+---------------------------+----------------------+ Row < DrdyUndefined , ev_DRDY_0 , Drdy0 , none , none >, Row < DrdyUndefined , ev_DRDY_1 , Drdy1 , none , none >, Row < Drdy0 , ev_DRDY_0 , none , none , none >, Row < Drdy0 , ev_DRDY_1 , Drdy1 , none , none >, Row < Drdy1 , ev_DRDY_0 , Drdy0 , none , none >, Row < Drdy1 , ev_DRDY_1 , none , none , none >, // +----------------+-------------------+----------------+---------------------------+----------------------+ // Region 2 // +----------------+-------------------+----------------+---------------------------+----------------------+ // Start Event Next Action Guard // +----------------+-------------------+----------------+---------------------------+----------------------+ Row < AllOk , Spi::Reply , ErrorMode , none , IsECFailed > // +----------------+-------------------+----------------+---------------------------+----------------------+ > {}; // clang-format on

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[Circular Buffer] Why doesn't have “emplace” interface?
by Марсель Галимуллин 16 Oct '20

16 Oct '20

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Boost configuration for VS Code / MacOS X Catalina
by Stefano Gragnani 12 Oct '20

12 Oct '20

Hi, how should i configure vs code to use Boost? I tried to compile the following example: #include <iostream> #include <boost/multiprecision/float128.hpp> #include <boost/math/special_functions/gamma.hpp> int main() { using namespace boost::multiprecision; // Operations at 128-bit precision and full numeric_limits support: float128 b = 2; // There are 113-bits of precision: std::cout << std::numeric_limits<float128>::digits << std::endl; // Or 34 decimal places: std::cout << std::numeric_limits<float128>::digits10 << std::endl; // We can use any C++ std lib function, lets print all the digits as well: std::cout << std::setprecision(std::numeric_limits<float128>::max_digits10) << log(b) << std::endl; // print log(2) = 0.693147180559945309417232121458176575 // We can also use any function from Boost.Math: std::cout << boost::math::tgamma(b) << std::endl; // And since we have an extended exponent range we can generate some really large // numbers here (4.02387260077093773543702433923004111e+2564): std::cout << boost::math::tgamma(float128(1000)) << std::endl; // // We can declare constants using GCC or Intel's native types, and the Q suffix, // these can be declared constexpr if required: constexpr float128 pi = 3.1415926535897932384626433832795028841971693993751058Q; return 0; } but that's what I get: Executing task: g++-10 -g -std=c++17 '-fext-numeric-literals' main.cpp -L/usr/local/Cellar/gcc/10.2.0/lib/gcc/10/ -lquadmath -o main.out < main.cpp:2:10: fatal error: boost/multiprecision/float128.hpp: No such file or directory 2 | #include <boost/multiprecision/float128.hpp> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ compilation terminated. The terminal process "/bin/zsh '-c', 'g++-10 -g -std=c++17 '-fext-numeric-literals' main.cpp -L/usr/local/Cellar/gcc/10.2.0/lib/gcc/10/ -lquadmath -o main.out'" failed to launch (exit code: 1). My task.json is: { // See https://go.microsoft.com/fwlink/?LinkId=733558 <https://go.microsoft.com/fwlink/?LinkId=733558> // for the documentation about the tasks.json format "version": "2.0.0", "tasks": [ { "label": "Build with g++ 10", "type": "shell", "command": "g++-10", "args": [ "-g", "-std=c++17", "'-fext-numeric-literals'", "main.cpp", "-L/usr/local/Cellar/gcc/10.2.0/lib/gcc/10/", "-lquadmath", "-o", "main.out" ], "group": { "kind": "build", "isDefault": true } }, { "label": "Build with Intel ICC", "type": "shell", "command": "icc", "args": [ "-g", "-std=c++17", "main.cpp", "-o", "main.out" ], "group": { "kind": "build", "isDefault": true } }, { "label": "Run Project", "type": "shell", "command": "./main.out", "group": { "kind": "build", "isDefault": true } } ] } And my c_cpp_properties.json is: { "configurations": [ { "name": "Mac", "includePath": [ "${workspaceFolder}/**", "/usr/local/Cellar/boost/1.73.0/include/**" ], "defines": [], "macFrameworkPath": [], "compilerPath": "/usr/local/bin/g++-10", "cStandard": "gnu18", "cppStandard": "gnu++14", "intelliSenseMode": "gcc-x64" } ], "version": 4 } Thanks Stefano Gragnani

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