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hash_value( complex<T> )
by Peter Dimov 19 Oct '21

19 Oct '21

At the moment, boost::hash_value for complex<T> is specified as When T is a built in type and val.imag() == 0, the result is equal to hash_value(val.real()). Otherwise an unspecified value, except that equal arguments shall yield the same result. This is a bit odd; the natural implementation for a two-argument point/tuple type is std::size_t seed = 0; boost::hash_combine( seed, v.real() ); boost::hash_combine( seed, v.imag() ); return seed; Can anyone offer an opinion on whether or why the original behavior is preferable?

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regarding boost::exception
by rajesh daggumati 18 Oct '21

18 Oct '21

Hi Team, I need to create an object for catched exception . class exception: virtual public std::exception ,virtual public boost::exception {} inside my application code, try{ boost::rethrow_exception(exceptr)} catch(std::exception &e) { std::exception *e = stacktoHeapObject(e); } static std::exception* stacktoHeapObj(std::exception* e) { if (dynamic_cast<std::bad_alloc*>(e)) { return new std::bad_alloc(*(dynamic_cast<std::bad_alloc*>(e))); } else if (dynamic_cast<std::bad_cast*>(e)) { return new std::bad_cast(*(dynamic_cast<std::bad_cast*>(e))); } else if (dynamic_cast<std::bad_typeid*>(e)) { return new std::bad_typeid(*(dynamic_cast<std::bad_typeid*>(e))); } else if (dynamic_cast<std::bad_exception*>(e)) { return new std::bad_exception(*(dynamic_cast<std::bad_exception*>(e))); } else if (dynamic_cast<std::domain_error*>(e)) { return new std::domain_error(*(dynamic_cast<std::domain_error*>(e))); } else if (dynamic_cast<std::invalid_argument*>(e)) { return new std::invalid_argument(*(dynamic_cast<std::invalid_argument*>(e))); } else if (dynamic_cast<std::length_error*>(e)) { return new std::length_error(*(dynamic_cast<std::length_error*>(e))); } else if (dynamic_cast<std::out_of_range*>(e)) { return new std::out_of_range(*(dynamic_cast<std::out_of_range*>(e))); } else if (dynamic_cast<std::overflow_error*>(e)) { return new std::overflow_error(*(dynamic_cast<std::overflow_error*>(e))); } else if (dynamic_cast<std::range_error*>(e)) { return new std::range_error(*(dynamic_cast<std::range_error*>(e))); } else if (dynamic_cast<std::underflow_error*>(e)) { return new std::underflow_error(*(dynamic_cast<std::underflow_error*>(e))); } else if (dynamic_cast<std::runtime_error*>(e)) { return new std::runtime_error(*(dynamic_cast<std::runtime_error*>(e))); } else if (dynamic_cast<std::exception*>(e)) { return new std::exception(*(dynamic_cast<std::exception*>(e))); } } I have coded by taking order reference of below pic. please help me to get classes names in boost:exception which are not in std::exception . if they are in boost::exception only then how to catch that and send to stackToHeapObj and what order i need to follow to add those if checks. try { boost::rethrow_exception(exptr) } here in catch block , we don't know which exception type we have in exptr(ie. std:: or boost:;) then How to catch them. if i use std::exception in catch block then if exptr throws boost::exception type then ... and viceversa..? Please help me to clarify above queries [image: image.png]

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Opinions on merging Assert, StaticAssert, ThrowException into Core
by Nikita Kniazev 17 Oct '21

17 Oct '21

Recently Core grew with additional dependencies on StaticAssert (in 1.76) and ThrowException (in the next release), previously it was only depending on Assert and Config. That made a lot of libraries checkout the same four repositories, three of them containing only a few headers. Merging into a single dependency will affect mostly positive about 100 libraries and negative 1: StlInterfaces (depends on Assert, and will on Core). Please leave a comment at https://github.com/boostorg/core/issues/97 if you think it is a good idea, or have concerns against doing that.

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No more cycles going forward
by Glen Fernandes 16 Oct '21

16 Oct '21

Boost 1.77.0 released with no dependency cycles between libraries. This wasn't easy to achieve and we want to preserve it, going forward. We should not regress and allow libraries to introduce dependency cycles in any future Boost release. i.e. Doing so should be considered a release blocker. Currently, such a regression exists (introduced last month in Context): Asio -> Coroutine -> Context -> Asio It should be fixed before we lock the branches for the 1.78 release, or we should not take this change in the release. Glen

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[Q] Help needed with boost::log, filters and a custom sink backend
by Volker 15 Oct '21

15 Oct '21

Dear Boost experts! I'm new to this list, so please have mercy if I'm not yet familiar with your best practices. Recently, I have been pulling my hair out while trying to use boost::log for a severity-logger-type functionality where the sink backend is not compatible with std::ostream. Best bet was to implement a custom sink backend that does the job in its consume() member. However, I can't get the attribute value for the severity level extracted to an int. For sure, there's something totally obvious I'm missing... Here's the source code (slightly abbreviated): #include <string> #include <boost/log/core.hpp> #include <boost/log/expressions.hpp> #include <boost/log/sinks/basic_sink_backend.hpp> #include <boost/log/sinks/sync_frontend.hpp> #include <boost/log/sources/logger.hpp> #include <boost/log/sources/severity_logger.hpp> #include <boost/log/trivial.hpp> #include <boost/smart_ptr/make_shared_object.hpp> #include <boost/smart_ptr/shared_ptr.hpp> namespace logging = boost::log; namespace sinks = boost::log::sinks; void SomeLogChannel(int severity, const std::string& message) {} class SinkBackend : public sinks::basic_sink_backend<sinks::synchronized_feeding> { public: explicit SinkBackend() {} void consume(logging::record_view const& rec) { std::string message = *rec[boost::log::expressions::smessage]; int severity = 0; if (rec.attribute_values().count("Severity")) { // severity = rec.attribute_values()["Severity"].extract<int>(); // cannot convert from 'boost::log::v2s_mt_nt6::value_ref<T,TagT>' to 'int' with T=int, TagT=void } SomeLogChannel(severity, message); } }; void init_logging() { typedef sinks::synchronous_sink<SinkBackend> sink_t; boost::shared_ptr<logging::core> core = logging::core::get(); boost::shared_ptr<SinkBackend> backend(new SinkBackend()); boost::shared_ptr<sink_t> sink(new sink_t(backend)); core->add_sink(sink); core->set_filter(logging::trivial::severity >= logging::trivial::error); } int main(int, char* []) { init_logging(); boost::log::sources::severity_logger< logging::trivial::severity_level > lg; BOOST_LOG_SEV(lg, logging::trivial::trace) << "Trace message"; BOOST_LOG_SEV(lg, logging::trivial::error) << "Error message"; return 0; } If this is a clumsy approach and there's a more elegant solution to feed log messages into SomeLogChannel() (in reality, it's a bit more complex because it involves a class, a couple interfaces, etc.), don't hesitate to comment as well. I'm still trying to wrap my mind around the topic. Thanks a bunch in advance and greets, Volker -- @: boost(a)bartheld.net

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regarding spurious wakeup in boost 1.76
by Daggumati, Rajesh 13 Oct '21

13 Oct '21

HI Team, I have been facing an issue regarding conditionvariable.timed_wait() This function is returning false everywhere in my code(windows platform). It not waiting for notify signal. conditionvariable.timed_wait(lock1,boost::posix_time::milliseconds(100)) I have found same issue information in google. [Thread] thousands of spurious wakeups from timed_wait() per second (narkive.com)<https://boost-users.boost.narkive.com/xu7advkY/thread-thousands-of-spurious…> did this issue get fixed in boost 1.76.0? Please help me how to fix this issue. Regards, Rajesh D Please be advised that this email may contain confidential information. If you are not the intended recipient, please notify us by email by replying to the sender and delete this message. The sender disclaims that the content of this email constitutes an offer to enter into, or the acceptance of, any agreement; provided that the foregoing does not invalidate the binding effect of any digital or other electronic reproduction of a manual signature that is included in any attachment.

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Evolving Boost.ContainerHash
by Peter Dimov 13 Oct '21

13 Oct '21

I've been thinking of updating and evolving Boost.ContainerHash, so I e-mailed Daniel James to see what his thoughts on that are. He says he's not going to come back to it, since he's moved on from C++. (Why would anyone do so is beyond me. :-)) More specifically, what I'm envisaging is updating boost::hash to take a seed: template<class T> struct hash { hash(); // as before explicit hash( size_t seed ); size_t operator()(T const& v) { return detail::hash_combine(seed, hash_value(v)); } }; The public hash_combine then becomes: template<class T> void hash_combine( size_t& seed, T const& v ) { return hash<T>(seed)(v); } This allows passing seeded hashes to unordered containers, without any changes to the latter: std::unordered_map<std::string, int, boost::hash<std::string>> map( 0, boost::hash<std::string>( 0x12345678 ) ); Seeding user-exposed hash tables is a good security practice which prevents (or makes less likely) some DoS attacks. The combiner function, detail::hash_combine, will also need to be updated to something that is state of the art for 2021, rather than for 2004. (ContainerHash is already using a more modern implementation of hash_combine, but not in all cases.) The implementation can be cleaned up by removing the C++98 era workarounds for compilers not supporting partial specialization, function template ordering, or argument-dependent lookup. The documentation is also due to a refresh, as the mentions of TR1 are no longer relevant. I also think that Boost.ContainerHash should just be renamed to Boost.Hash as that's what it is - it defines boost::hash. So, I am thinking of taking over ContainerHash and doing all that, if there are no objections.

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[CMake] Can/should we specify optional dependencies
by John Maddock 11 Oct '21

11 Oct '21

I have a regex bug report relating to linking to ICU when using CMake: https://github.com/boostorg/regex/issues/143 Is there a correct way to specify in the CMake file that if you use header X, then you should also link to library Y, but otherwise not? Thanks, John. -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

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Boost::posixtime issue
by mahesh pramod 07 Oct '21

07 Oct '21

Hi , I am getting false always for this timed_wait function . does posix_time supports in windows as its not looking for notify signal. scoped_lock_t lock(m_mutex); EXPECT_TRUE(m_condition_variable.timed_wait(lock, boost::posix_time::milliseconds(500))) << "Should get signalled (true) not time out";

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boost::posix_time issue
by mahesh pramod 06 Oct '21

06 Oct '21

Hi , I am getting false always for this timed_wait function . does posix_time supports in windows as its not looking for notify signal. scoped_lock_t lock(m_mutex); EXPECT_TRUE(m_condition_variable.timed_wait(lock, boost::posix_time::milliseconds(500))) << "Should get signalled (true) not time out";

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