June 2017 - Boost-users - lists.preview.boost.org

[MSM] exception_caught question
by Christophe Henry 10 Jun '17

10 Jun '17

Hi, > I found that answer for exceptions which can occur during the processing: > >https://lists.boost.org/boost-users/2012/03/73904.php > >Here is handled the case that exception is derived from std::exception. >What happens if not? >Can the parameter be changed to std::exception_ptr or just a > template Parameter? only std::exception are caught. Others just go through and interrupt the transition, which might leave the state machine in a dirty state, where an entry or exit action would not have been called. Cheers, Christophe

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Beginner Question (Windows MSVC)
by James Stortz 09 Jun '17

09 Jun '17

I can't seem to include/link and compile properly. I am using boost 1.64 and Visual Studio 2017 (Community). I can successfully include the headers and compile the example program on the Getting Started page[1]. But when trying to simply compile the mutex example from interprocess docs[2], I get this error: LINK : fatal error LNK1104: cannot open file `libboost_date_time-vc141-mt-2-1_64.lib` >From the Getting Started page on linking, I have been trying the following: cl /EHsc /I boost_1_64_0 doc_memtest1.cpp ^ /link /LIBPATH:F\src\boost_1_64_0\stage\lib I have even tried a solution from Stackoverflow[3], multiple times with various configurations, x64/x86, but nothing. I don't even have that particular library. I have "libboost_date_time-vc141-mt-gd-1_64.lib" and "libboost_date_time-vc141-mt-1_64.lib". I assume I am doing something wrong, as I am new to programming on Windows/MSVC. Any help? Thanks! James [1] http://www.boost.org/doc/libs/1_64_0/more/getting_started/windows.html [2] http://www.boost.org/doc/libs/1_64_0/doc/html/interprocess/synchronization_… [3] https://stackoverflow.com/questions/41464356/build-boost-with-msvc-14-1-vs2…

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[ Boost.Units ] Invert a quantity_type
by Belcourt, Kenneth 09 Jun '17

09 Jun '17

Hi, I have a structure that is passed some type from which I can extract a units quantity type: template <typename Field> struct field { Field f; typedef typename Field::quantity_type quantity_type; // access typed data off Field quantity_type operator[](int i) { return f[i]; } }; Is there a way to invert a quantity type so I can compute and return, say, the inverse of the passed quantity_type? So, for example, is there any Boost.Units inverse meta like function that might let me say something like this: template <typename Field> struct field_inverse { Field f; typedef typename Field::quantity_type quantity_type; typedef typename bu::inverse<quantity_type>::type inverse_quantity_type; // access typed data off field, return inverse of quantity_type inverse_quantity_type operator[](int i) { return one / f[i]; } }; I’m hoping for something more general than partially specializing the bu::inverse method for each quantity I may want to invert. Any ideas? — Noel Belcourt

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[Boost.Heap] Possible bug with ordered iterator and boost::heap::binomial_heap
by Kudo, Jun 08 Jun '17

08 Jun '17

Hi all, I'm observing a weird phenomenon when iterating over a binomial heap after pushing two values with the same priority. Instead of printing the expected values twice, the ordered iterator seems to print three values. I do not observe this behavior when using a Fibonacci heap or a binary heap. I've attached sample code that demonstrates this behavior. Can anyone help explain what's going on? Boost Version : Boost 1.64 Compiler : GCC 5.3.0 #include <iostream> #include "boost/heap/fibonacci_heap.hpp" #include "boost/heap/binomial_heap.hpp" #include "boost/heap/d_ary_heap.hpp" template <class HeapType> void PrintHeap(HeapType const & heap) { std::cout << "Printing out heap : "; for (auto it = heap.begin(); it != heap.end(); ++it) { std::cout << *it << " "; } std::cout << "\n Printing out heap in order : "; for (auto it = heap.ordered_begin(); it != heap.ordered_end(); ++it) { std::cout << *it << " "; } std::cout << "\n\n"; } int main(int /* argc */, char** /* argv */) { typedef boost::heap::binomial_heap<int> BinomialHeap; BinomialHeap binomial_heap; binomial_heap.push(1); binomial_heap.push(1); // Prints {1,1} and {1,1,1} PrintHeap(binomial_heap); typedef boost::heap::fibonacci_heap<int> FibonacciHeap; FibonacciHeap fibonacci_heap; fibonacci_heap.push(1); fibonacci_heap.push(1); // Prints {1,1} and {1,1} PrintHeap(fibonacci_heap); typedef boost::heap::d_ary_heap<int, boost::heap::arity<2>, boost::heap::mutable_<true>> BinaryHeap; BinaryHeap binary_heap; binary_heap.push(1); binary_heap.push(1); // Prints {1,1} and {1,1} PrintHeap(binary_heap); } Thanks! Jun

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svn.boost.org schedule maintenance - DOWN TIME
by Michael Caisse 07 Jun '17

07 Jun '17

Hi all - svn.boost.org is scheduled for maintenance on June 8 from 1700 - 1900 UTC. Expect outages for Trac during this time. Happy coding! michael -- Michael Caisse Ciere Consulting ciere.com

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[MSM] What happens to MSM if guard returns `false`, mutable events and error recovery?
by Ovanes Markarian 05 Jun '17

05 Jun '17

Hi *, I am currently reading through the MSM docs and have one question, what happens to MSM if guard returns `false`. Does the MSM enter an error state in orthogonal region (http://www.boost.org/doc/ libs/1_64_0/libs/msm/doc/HTML/ch03s02.html#d0e577)? Even internals page describes, what happens if guard returns `true`, but not a single word on `false` case. Regarding the const events: I am programming an MSM to proxy network traffic and once a message with data was received it'll be analysed and moved between different states. Message instances implement move semantics. Currently, the MSM has an initial state `ready` where the `message_in` event is handled. This event contains the message to be analysed. From my current understanding I either have to make message field in `message_in` event mutable or MSM needs to to support r-value references. Can somebody tell me what's going to happen if the action only accepts r-value reference to an event instance? Currently, it seems to work, but would like to understand the implications. struct some_action_impl { template<class Fsm, class Event, class SourceState, class TargetState> void operator()(Event&& ev, Fsm& fsm, SourceState& source, TargetState& target) { ... } } My last question relates to multi-threading. I understand that MSM manages internal states, would it be safe to create MSM as a thread-local storage and restart the thread-local MSM if the new request comes in? It's more about, what happens to MSM after an error state? Is calling stop(), start() members enough? Many thanks for help, Ovanes

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[MSM] exception_caught question
by Ovanes Markarian 05 Jun '17

05 Jun '17

Hi *, I found that answer for exceptions which can occur during the processing: https://lists.boost.org/boost-users/2012/03/73904.php Here is handled the case that exception is derived from std::exception. What happens if not? Can the parameter be changed to std::exception_ptr or just a template parameter? Thanks for help, Ovanes

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[Units] What is the correct/recommended way to handle different ratios in the same unit
by Carel Combrink 05 Jun '17

05 Jun '17

Hi All, I have recently started looking at Boost.Units to use in my applications where unit conversions happens regularly. The conversions are mostly within the same unit, but different ratios, like hertz to killohertz and back (also distances). I have asked for some advice on StackOverflow, but still waiting for an answer to either indicate the correct way or confirm that what I am doing is correct. The mentioned question can be seen here: https://stackoverflow.com/q/44300549/991000 Is there someone that can perhaps look at my question on SO and offer some assistance or advice please? Regards, Carel

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Boost.Parameter python and lazy evaluation of default arguments
by Philipp.Buettgenbach＠gmail.com 05 Jun '17

05 Jun '17

Hello all, I have a question concerning the Boost.Parameter library and the python binding provided by this library. When I try to compile the attached code with clang I get: ------------------------------- /tmp$ clang -I/usr/include/python2.7/ -std=c++14 -c python_test.cpp In file included from python_test.cpp:7: In file included from /usr/include/boost/parameter/preprocessor.hpp:8: In file included from /usr/include/boost/parameter/parameters.hpp:40: /usr/include/boost/parameter/aux_/arg_list.hpp:361:16: error: no viable conversion from 'boost::parameter::aux::maybe<std::basic_string<char> >' to 'const std::basic_string<char>' return arg.value; ^~~~~~~~~ ------------------------------- If I just compile main or use standard default arguments everything compiles fine. Can anybody explain to me what's wrong with using lazy default argument evaluation when exporting to python? Thanks a lot, Philipp

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Source incompatible changes in Boost.Test
by Dominique Devienne 03 Jun '17

03 Jun '17

What's the point of changing a public symbol's case like this, leading to a hard build error? Seems a bit gratuitous, no? And not up to Boost's standards I might add. --DD if (BOOST_VERSION < 106000) boost::unit_test::tut_suite #else boost::unit_test::TUT_SUITE #endif

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