April 2014 - Boost-users - lists.boost.org

[interprocess] Determine size of managed_shared_memory
by Kai Benndorf 12 Oct '19

12 Oct '19

Hi all, I want to create a managed_shared_memory in exactly the size I needed. Therefore I do something like this: size = sizeof( common_managed_shared_memory ); size += sizeof( MyClassInSharedMem ); managed_shared_memory segment(create_only, "name", size ); MyClassInSharedMem allocates itself some memory by segment->allocate(). I added this also to the size, but get a boost::interprocess::bad_alloc exception on allocating this additional memory. Are there some magic bytes I forgot to add? Many thanks in advance Kai

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[Range, Phoenix] What am I missing...
by Robert Jones 25 Apr '17

25 Apr '17

Hi Folks Can anyone explain the output of this program... #include <iostream> #include <boost/range/algorithm/copy.hpp> #include <boost/range/counting_range.hpp> #include <boost/range/adaptor/reversed.hpp> #include <boost/range/adaptor/transformed.hpp> #include <boost/phoenix/bind/bind_function.hpp> #include <boost/phoenix/core/argument.hpp> int f( int i ) { return i * 2; } int main( ) { using boost::adaptors::reversed; using boost::adaptors::transformed; using boost::counting_range; using boost::copy; using boost::phoenix::arg_names::_1; copy( counting_range( 1, 5 ) | reversed | transformed( f ), std::ostream_iterator<int>( std::cout, " " ) ); std::cout << std::endl; copy( counting_range( 1, 5 ) | reversed | transformed( bind( f, _1 ) ), std::ostream_iterator<int>( std::cout, " " ) ); std::cout << std::endl; } Which is... 8 6 4 2 1768406272 1768406272 1768406272 1768406272 I'm using Gcc 4.6.2 & Boost 1.53 Thx All.

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[statechart] Passing parameters from event to State Local Storage
by Christophe Bourez 16 Nov '16

16 Nov '16

I need to maintain a parameter into the state local storage. This parameter is initially contained in the event that causes the transition to the target state. I give hereafter a small illustrative example. typename sc = boost::statechart; class EvTest : public sc::event<EvTest> { public: EvTest(std::size_t val) : value(val) {} std::size_t getValue() const { return this->value; } private: std::size_t value; }; class MyStateMachine; class StSource; class StTarget; class StSource : public sc::simple_state<StSource, MyStateMachine> { public: typedef sc::custom_reaction<EvTest> reactions; sc::result react(const EvTest &event) { // How to pass event.getValue() to the target state ? transit<StTarget>(); } }; class StTarget : public sc::simple_state<StTarget, MyStateMachine> { public: StTarget(std::size_t val) : val(value) {} private: std::size_t value; }; Thanks, Christophe

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Re: [Boost-users] lexical_cast between double and string slow in Visual Studio 2013
by David Roberts 07 May '15

07 May '15

> That issue is unknown. I'd really appreciate the investigation. I have done some more investigation, and there are two factors that only cause the slowness when they both occur together. > Try excluding the lexical_cast from test, I have a feeling that this is only MSVC related issue: > > #include <sstream> > #include <string> > > int main (int, char **) > { > for (double count = 0.0; count < 1000000.0; count += 1.41) > { > std::stringstream ss; > ss << count; > std::string result = std::move(ss.str()); > ss.str(std::string()); > > ss << result; > ss >> count; > } > > return 0; > } > Running your test program does not exhibit the problem. It runs in around 3 seconds on my machine when built with either Visual Studio 2010 or Visual Studio 2013. However, changing it very slightly to match more closely what lexical_cast does internally does recreate the problem: #include <sstream> #include <string> int main (int, char **) { for (double count = 0.0; count < 1000000.0; count += 1.41) { std::stringstream ss; ss.unsetf(std::ios::skipws); ss.precision(17); ss << count; std::string result = std::move(ss.str()); ss.str(std::string()); ss << result; ss >> count; } return 0; } The effect of setting the precision to 17 is that lots of 9s appear in the string representations. (The number 17 is what boost::detail::lcast_get_precision(double*) chooses.) Without the precision call the contents of the string called result start off like this: 0 1.41 2.82 4.23 5.64 7.05 8.46 9.87 11.28 12.69 With precision set to 17 they start off like this: 0 1.4099999999999999 2.8199999999999998 4.2299999999999995 5.6399999999999997 7.0499999999999998 8.4599999999999991 9.8699999999999992 11.279999999999999 12.69 This happens for both Visual Studio 2010 and Visual Studio 2013. Then the next difference is that Visual Studio 2013 spends a lot longer handling all the extra 9s. Changing the program so that the double is converted to a string using std::stringstream without a precision call and then back to double using lexical_cast takes about 3 seconds for both Visual Studio 2010 and Visual Studio 2013. It is the combination of having all the extra 9s to parse and using Visual Studio 2013 that makes the test using lexical_cast to go both ways slow. Both Visual Studio 2010 and Visual Studio 2013 do the conversion by calling std::num_get<char,std::istreambuf_iterator<char,std::char_traits<char> > >::do_get() which then calls a function called _Stodx() which is implemented in xstod.c. This function is very different for the two versions. In Visual Studio 2010 it's a relatively thin wrapper around the C function strtod(). In Visual Studio 2013 _Stodx() has got a completely new implementation that's generated by #including xxstod.h with some macros defined. The original C function strtod() is much faster than the new _Stodx() when there are lots of 9s at the end of the strings being parsed. This modification to the program: #include <sstream> #include <string> #include <stdlib.h> int main (int, char **) { for (double count = 0.0; count < 1000000.0; count += 1.41) { std::stringstream ss; ss.unsetf(std::ios::skipws); ss.precision(17); ss << count; std::string result = std::move(ss.str()); ss.str(std::string()); ss << result; char *endptr; count = strtod(ss.str().c_str(), &endptr); } return 0; } has a runtime of about 3 seconds even though it's got to cope with all the 9s. I guess only someone from Microsoft or Dinkumware could comment on why _Stodx() was reimplemented. But the other thing is that by setting precision to 17 lexical_cast is bloating the string representations of the doubles with lots of 9s in both Visual Studio 2010 and Visual Studio 2013. Setting precision to 15 instead prevents this, and makes the original test run faster even with Visual Studio 2013 (about 4 seconds rather than 10). Regards, David

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Statechart serialization
by mbrodeur65 04 Mar '15

04 Mar '15

Hi, I'm looking for a solution to serialize boost::statechart objects. I'm aware that this feature is on the statechart library todo list but was wondering if there are any workaround to achieve this with the latest boost release (1.34) ? thanks for your help ! mbrodeur65 -- View this message in context: http://www.nabble.com/Statechart-serialization-tf4131326.html#a11749139 Sent from the Boost - Users mailing list archive at Nabble.com.

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NT² 3.0 and Boost.SIMD - Stable release
by Joel Falcou 21 Nov '14

21 Nov '14

The first stable release of the 3.x series of MetaScale’s open-source software is available: NT² 3.0. It also includes its spin-off project, Boost.SIMD (not yet a Boost library). Many Issues have been closed since last beta. The main focus of this release cycle was to fix performances issues and to stabilize some parts of the API. Next step will be to separate NT2 and Boost.SIMD into separate repositories, thus making one more step toward Boost.SIMD submission into review. [ http://www.metascale.org/nt%C2%B2-3-0-and-boost-simd ] *Changes & Bug Fixes:* - Major performance improvements in both libraries - Added experimental support for the HPX runtime for parallelization on shared memory systems - Optimizations of many elemental functions, in particuler log/ex, frexp/ldexp and cbrt - More advanced shuffle pattern recognition for SIMD - Fixed issues with Visual Studio 2013 - More functions are force-inlined to ensure good performance - New functions for conversion between types and mixing of vectors of different sizes - Demo applications usable as benchmarks - Better handling of errors when an unsupported function is called - New API for custom memory allocators Full changelog is available at https://github.com/MetaScale/nt2/releases/tag/3.0.0. *How to get it ?* - Source and binary packages can be downloaded here: http://nt2.metascale.org/downloads - The release is also available on Github : https://github.com/MetaScale/nt2/releases - The main master branch is still under development : https://github.com/MetaScale/nt2

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[Thread] Read-write locks
by lfrfly＠icqmail.com 17 Sep '14

17 Sep '14

I'm trying to create a standard read/write lock using Boost Threads, and I'm having a bit of difficulty mapping the Boost concepts onto the usual ones. A read/write lock should have several states: Locked for reading (multiple threads may lock at once), locked for writing (only one thread may lock, and no threads may be locked for reading at the same time), and unlocked. Ideally it would be nice if an RWL which is locked for reading may temporarily upgrade to locked for writing, then return to the locked for reading state. Boost supports several relevant notions of locking: shared locking, upgrade locking, and exclusive locking. This to me is a confusing distinction. In particular, a shared_mutex seems appropriate as the basis for a RWL, but is lock_upgrade() the equivalent of a write lock and lock_shared the equivalent of a read lock? This is unclear. If "upgrade locking" is not the same as "exclusive locking", then is an upgrade lock actually exclusive? Could someone please clarify this.

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[Statechart] How to decide between post_event and process_event atrun time ?
by Philippe DAVID 22 Jul '14

22 Jul '14

Hi, I have a method in which I want to post/process an event. The thing is, this method can be called from outside the state machine (so I need to call process_event), or indirectly by a reaction of the state machine (in this case I must call post_event since process_event is not reentrant). I don't want to write 2 distinct methods to do this (one that calls post, and the other process), I would much rather prefer adding a 'if' in my method that tells me if I have to call process_event or post_event (if I'm being called indirectly by the state machine or not). Is there a way to do this with statechart ? regards, Philippe

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[Log] Extract severity value
by Olivier Tournaire 17 Jul '14

17 Jul '14

Hi all, I am trying to extract severity level from a log record, but i seems that I am doing it the wrong way. Here is the code I use: void LogDockWidget::receiveLog(boost::log::record_view const& rec, const std::string& log) { logging::value_ref< logging::trivial::severity_level > level = logging::extract< logging::trivial::severity_level >("Severity", rec); // ... } Here level.get() always returns "info". All my logs are done with the BOOST_LOG_TRIVIAL(...) macro. The formatter whereas displays correctly the severity level. Here is how it is defined: void LogDockWidget::init_logging() { boost::shared_ptr< logging::core > core = logging::core::get(); typedef sinks::synchronous_sink< QTextEditFormattedSinkBackend > sink_t; boost::shared_ptr< sink_t > sink(new sink_t); // ... logging::add_file_log( keywords::file_name = logFilename, keywords::auto_flush = true, keywords::format = ( BUILD_LOG_FORMATTER() ) ); sink->set_formatter( BUILD_LOG_FORMATTER() ); core->add_sink(sink); // Add attributes that we will use logging::add_common_attributes(); core->add_global_attribute( "ThreadID", attrs::current_thread_id()); } #define BUILD_LOG_FORMATTER() \ expr::stream \ << "[" << expr::format_date_time< boost::posix_time::ptime >("TimeStamp", "%Y-%m-%d %H:%M:%S") << "] " \ << expr::attr<unsigned int>("LineID") << " " \ << ": <" << logging::trivial::severity << "> " \ << " [" << expr::attr<attrs::current_thread_id::value_type>("ThreadID") << "] " \ << expr::if_(expr::has_attr(scope_attribute)) \ [ \ expr::stream << "[" << scope_attribute << "] " \ ] \ << expr::message Could you please let me know what I am doing wrong? Regards, Olivier

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Autobahn for C++: RPC and PubSub
by Tobias Oberstein 24 Jun '14

24 Jun '14

Hi, I'm happy to anounce Autobahn|Cpp - another subproject of Autobahn (http://autobahn.ws) this time for C++ 11 / Boost. Autobahn|Cpp allows remote procedure calls and publish & subscribe messaging for C++ application components and uses boost::future, continuations and Boost/ASIO as underlying network library. Here is how app code looks like: https://github.com/tavendo/AutobahnCpp/blob/master/README.md#show-me-some-c… Using Autobahn|Cpp, you can e.g. call your C++ code from JavaScript running in a browser. And much more. This is an early alpha version, things aren't fully hashed out, but there are a couple of examples included here: https://github.com/tavendo/AutobahnCpp/blob/master/README.md#examples Cheers, /Tobias

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Fix for annoying bug / library maintenance
by Filip Konvička 30 May '14

30 May '14

Hi, https://svn.boost.org/trac/boost/ticket/4964 This is out there for years. To me this seems to be clearly explained and a fix is provided, but apparently all bugs assigned to 'bgubenko' aren't monitored (for years there has been no reaction). So is there a way of getting the fix ever applied? Or are such unmaintained libraries just doomed to eventually die, despite the efforts of the people reporting bugs and posting patches? Thanks, Filip

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[test]Legacy support - Boost 1.34.1 with MSVC 6
by Kerry, Richard 29 May '14

29 May '14

I've just started trying to use Boost's Test module. Trouble is I'm still stuck with Visual Studio 6(SP6), so I believe I need to stick with Boost 1.34.1 as the last properly supported for VC6. I'm having trouble getting the examples even to compile (ie exec_mon_example.cpp). Does anyone have any pointers to known incompatibilities between Boost 1.34.1 and VC6SP6 ? Or whether there is a more recent version where the Test module will work with VC6 ? I am well aware of how old VC6 is and would like to move forward. The major aim of getting Boost.Test working with VC6 is to give some confidence that any port to VC12 is working satisfactorily. Regards, Richard. Richard Kerry BNCS Engineer, SI SOL Telco & Media Vertical Practice T: +44 (0)20 3618 2669 M: +44 (0)7812 325518 Lync: +44 (0) 20 3618 0778 Room G300, Stadium House, Wood Lane, London, W12 7TA richard.kerry(a)atos.net<mailto:richard.kerry@atos.net>

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Boost test and openmpi
by Martin Vymazal 20 May '14

20 May '14

Hello, I have the following code: #define BOOST_TEST_DYN_LINK #define BOOST_TEST_MODULE mpi_functionality #include <boost/test/unit_test.hpp> #include "mpi.h" struct MPI_Functionality_Fixture { MPI_Functionality_Fixture() { m_argc = boost::unit_test::framework::master_test_suite().argc; m_argv = boost::unit_test::framework::master_test_suite().argv; } int m_argc; char** m_argv; }; BOOST_FIXTURE_TEST_SUITE( MPI_Functionality_TestSuite, MPI_Functionality_Fixture ) BOOST_AUTO_TEST_CASE( mpi_functionality_parenv_init ) { MPI_Init(&m_argc,&m_argv); } BOOST_AUTO_TEST_CASE( mpi_functionality_parenv_finalize ) { MPI_Finalize(); } BOOST_AUTO_TEST_SUITE_END() The code compiles fine, but I have the following problem when I try to run it. When I run as 'mpirun ./my_executable' or 'mpirun -np 3 ./my_executable' everything goes fine. On the other hand, when I run as ./my_executable I get the following error: unknown location(0): fatal error in "mpi_functionality_parenv_finalize": unrecognized signal Outside of Boost, it is perfectly possible to write a program which calls MPI_Init and MPI_Finalize and it does not have to be used with mpirun. I wonder if this (different) behavior of Boost test is normal. I did not find any remarks regarding Boost test and mpi in the tutorial. Best regards, Martin Vymazal

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[Test] Boost.Test for Property Tree Issue
by Pritesh Acharya 19 May '14

19 May '14

Boost version: 1.55.0 OS: Windows 8 IDE: Visual Studio 2010 I have a small class which just parses a std::string using boost::property_tree::read_json. I'm trying to test my method with invalid input to make sure my method handles the exception. However, when I execute GetPropertyTreeFromJsonInValidInput2 (source code in attachment), I get exception in the visual studio itself and I have to break the execution. (snapshot is included in attachment). I'm a new user of boost, so don't know where to look for the solution.

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"Trac thinks your submission might be Spam. To prove otherwise please provide a response to the following."
by Nico Schlömer 16 May '14

16 May '14

Hi all, I would like to make contributions to Boost on trac <https://svn.boost.org/trac/boost>, but whenever I would like to make comment a bug report, it gets recognized as spam, and I'm redirected to a captcha-page that I think should contain a captcha, but does _not_ <https://svn.boost.org/trac/boost/captcha#trac-add-comment>. Any hints? Cheers, Nico

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[Date Time] time_period has not default constructor
by Pablo Madoery 30 Apr '14

30 Apr '14

I am using the library Date Time, in particular the object time_period. I was wondering why (if there is a good reason) this class has not a default constructor. the default constructor result usefull when using for example a map with the operator [] or when using serialization from Boost. ptime class has default constructor. If a time_period is formed by two ptime objects, why time_period has not its default constructor as well. Thanks

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allocating shared memory fails beyond 8 GB
by vipin sachdeva 30 Apr '14

30 Apr '14

Hi, I am using managed_xsi_shared_memory to allocate memory as below: boost::interprocess::managed_xsi_shared_memory shmem(boost::interprocess::create_only, key, atol(argv[2])); For some reason, I cannot allocate more than 8 GB of memory. Both sysctl and ipcs have limits higher than that set (output below). ------ Shared Memory Limits -------- max number of segments = 1874919423 max seg size (kbytes) = 9765624999999 max total shared memory (kbytes) = 39999999999999996 min seg size (bytes) = 1 kernel.shmmax = 9999999999999999 kernel.shmall = 9999999999999999 kernel.shmmni = 1874919423 vm.hugetlb_shm_group = 0 Is there any reason why this allocation should fail ?

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[typeindex v3.0] Peer review begins Mon 21st ends Wed 30th
by Niall Douglas 30 Apr '14

30 Apr '14

Dear Boost, A second round of community review begins for proposed Boost.TypeIndex on Mon 21st, lasting ten days. I should apologise as it's my fault for starting another peer review straight after Boost.Align ends, however I was busy as Google Summer of Code admin until today, and I will be preparing to talk at C++ Now straight after this review ends. I hope that this doesn't affect the community's willingness to contribute to the review. Reminder of the report from the last TypeIndex v2.1 review: https://groups.google.com/forum/#!topic/boost-list/TeiSdkRkUF0 Reminder of the original peer review announcement: http://boost.2283326.n4.nabble.com/TypeIndex-Peer-review-period-for-li brary-acceptance-begins-ending-Thurs-21st-Nov-td4654788.html Source code: https://github.com/apolukhin/type_index/zipball/master Github: https://github.com/apolukhin/type_index Documentation: http://apolukhin.github.com/type_index/index.html Changes in TypeIndex v3.0 since v2.1 (from my own review of it): 1. Documentation is hugely improved over v2.1, lots of side by side examples illustrating the differences and similarities. 2. You can now create your own custom type indices using an extensible framework. 3. boost::typeind::type_info now exports raw_name() and pretty_name() to maximise MSVC-GCC compatibility, and to solve point 1 but not point 2 in the v2.1 report. 4. The undefined behaviour trick used in v2.1 has been replaced with a cast via the placeholder type boost::typeind::detail::ctti_data which can be viewed in https://github.com/apolukhin/type_index/blob/master/include/boost/type _index/ctti_type_index.hpp. There is an explanation in the comments there about this technique's compatibility with the C++ standard. 5. TypeIndex now defines everything in the boost::typeind namespace instead of the boost namespace. So: 1. What is your evaluation of the design? 2. What is your evaluation of the implementation? 3. What is your evaluation of the documentation? 4. What is your evaluation of the potential usefulness of the library? 5. Did you try to use the library? With what compiler? Did you have any problems? 6. How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? 7. Are you knowledgeable about the problem domain? And finally, every review should answer this question: 8. Do you think the library should be accepted as a Boost library? Be sure to say this explicitly so that your other comments don't obscure your overall opinion. Thanks, Niall -- Currently unemployed and looking for work in Ireland. Work Portfolio: http://careers.stackoverflow.com/nialldouglas/

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update cycle
by Philipp Kraus 30 Apr '14

30 Apr '14

Hello, I try to compile Boost myself under OSX and the thread library runs into compiler errors. I have seen that the fix is inserted into the repo, so I would like to wait to a new Boost release. The last Boost version (1.55.0) was released on November 2013, so my question is in which cycles are new releases created (half a year)? Thanks Phil

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Boost::Interprocess - using variadic template args with managed_shared_memory::construct()
by james 28 Apr '14

28 Apr '14

Hi, I'm trying to write a wrapper over some of boost::interprocess and I want to have a function like this: template <typename T, typename... Args> T* Wrapper::createStruct(const std::string& name, Args&&... args) { return m_shm->construct<T>(name.c_str())(std::forward<Args>(args)...); } This fails to compile as it seems boost::interprocess uses its own varargs scheme when I try to create the following struct in the SHM through this wrapper function: struct Custom { Custom(int a, int b) : m_a(a), m_b(b) { } int a; int b; } int main() { ... Custom* c = shm->createStruct("Custom", 1, 2); } The error message: /usr/include/boost/interprocess/detail/named_proxy.hpp:79:7: error: no matching function for call to ‘test_sharedmemory::sharedmemory_custom::test_method()::Custom::Custom()’ { new((void*)mem)T(boost::forward<Args>(get<IdxPack>(args_))...); } ^ /usr/include/boost/interprocess/detail/named_proxy.hpp:79:7: note: candidates are: /home/james/dev/infinityplus/test/common/shm/sharedmemory/main.cpp:136:7: note: test_sharedmemory::sharedmemory_custom::test_method()::Custom::Custom(int, int) Custom(int one, int two) ^ /home/james/dev/infinityplus/test/common/shm/sharedmemory/main.cpp:136:7: note: candidate expects 2 arguments, 0 provided Is there any way I can get this to work? I'd rather my wrapper's interface used std only. boost 1.55 c++11 g++ 4.8.2 TIA, James

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Announcing the student program for Meeting C++ 2014
by Jens Weller 28 Apr '14

28 Apr '14

Hello C++ and Boost Community, today I have the honor to announce the student program for Meeting C++ 2014: > The Meeting C++ Student program will enable 50 students to attend Meeting C++ 2014 plus 3 exclusive workshops organized by think-cell one day before the conference on December 4th. So, for students this will be a 3 day conference! After the workshops you will be invited to the student dinner by think-cell. Further details at http://meetingcpp.com/index.php/newsreader/items/meeting-cpp-2014-the-stude… kind regards, Jens Weller

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[Coroutine 1.54] Compile error with bool return from coroutine-function
by Rob Desbois 27 Apr '14

27 Apr '14

(Caveat: I've been unable to find anything about this; hopefully haven't missed anything obvious.) (Apology: I'm aware Coroutine has a new interface as of 1.55; I haven't determined whether it is also affected.) Given the following code: #include <cassert> #include <boost/bind.hpp> #include <boost/coroutine/coroutine.hpp> using coro_t = boost::coroutines::coroutine< bool() >; void get_a_bool( coro_t::caller_type& yield ) { while (true) yield(true); } int main() { coro_t producer( boost::bind(&get_a_bool, _1) ); assert( producer ); } I get this error on compilation (g++ 4.8.2, Boost 1.54): rob{code 0} 839# clear && g++ boost-coroutine-bool-return.cpp -g -W -Wall --std=c++11 -L. -lboost_context -lboost_coroutine -o boost-coroutine-bool-return In file included from /usr/include/boost/coroutine/v1/detail/coroutine_base_resume.hpp:26:0, from /usr/include/boost/coroutine/v1/detail/coroutine_base.hpp:21, from /usr/include/boost/coroutine/v1/coroutine.hpp:30, from /usr/include/boost/coroutine/coroutine.hpp:13, from boost-coroutine-bool-return.cpp:11: /usr/include/boost/coroutine/detail/holder.hpp: In instantiation of ‘struct boost::coroutines::detail::holder<bool>’: /usr/include/boost/coroutine/v1/detail/coroutine_base_resume.hpp:103:28: required from ‘void boost::coroutines::detail::coroutine_base_resume<Signature, D, void, 1>::resume(boost::coroutines::detail::coroutine_base_resume<Signature, D, void, 1>::arg_type) [with Signature = void(bool); D = boost::coroutines::detail::coroutine_base<void(bool)>; boost::coroutines::detail::coroutine_base_resume<Signature, D, void, 1>::arg_type = bool]’ /usr/include/boost/coroutine/v1/detail/coroutine_op.hpp:268:9: required from ‘D& boost::coroutines::detail::coroutine_op<Signature, D, void, 1>::operator()(boost::coroutines::detail::coroutine_op<Signature, D, void, 1>::arg_type) [with Signature = void(bool); D = boost::coroutines::coroutine<void(bool), 1>; boost::coroutines::detail::coroutine_op<Signature, D, void, 1>::arg_type = bool]’ boost-coroutine-bool-return.cpp:29:13: required from here /usr/include/boost/coroutine/detail/holder.hpp:39:14: error: ‘boost::coroutines::detail::holder<Data>::holder(boost::coroutines::detail::coroutine_context*, bool) [with Data = bool]’ cannot be overloaded explicit holder( coroutine_context * ctx_, bool force_unwind_) : ^ /usr/include/boost/coroutine/detail/holder.hpp:35:14: error: with ‘boost::coroutines::detail::holder<Data>::holder(boost::coroutines::detail::coroutine_context*, Data) [with Data = bool]’ explicit holder( coroutine_context * ctx_, Data data_) : At a glance it looks like there's no way a coroutine-function could possibly return bool due to the overload collision. Is this right? Did I miss something completely obvious in the docs? It's easy enough to work around with a transparent bool wrapper, I just want to be sure I'm not being a muppet :-D TIA -- rob -- Rob Desbois http://theotherbranch.wordpress.com/

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Boost PropertyTree: read_json() followed by write_xml produces invalid XML
by Marcel Loose 27 Apr '14

27 Apr '14

Hi all, I was quite surprised and disappointed to find out that I was unable to convert a simple JSON file into XML, using the Boost PropertyTree. As input I used the example JSON file from the documentation (see example.json below). I wrote a small program (see example.cc below) that reads in this JSON file, writes it to disk as XML file, and finally tries to read back this XML file. This last operation fails with an exception (see output below); the XML file that is produced (see example.xml below) is invalid, because it contains empty tags (<>). Am I doing something wrong? Best regards, Marcel Loose. $ cat example.json { "menu": { "foo": true, "bar": "true", "value": 102.3E+06, "popup": [ {"value": "New", "onclick": "CreateNewDoc()"}, {"value": "Open", "onclick": "OpenDoc()"} ] } } $ cat example.cc #include <boost/property_tree/ptree.hpp> #include <boost/property_tree/json_parser.hpp> #include <boost/property_tree/xml_parser.hpp> #include <fstream> using namespace std; using namespace boost::property_tree; int main() { ptree pt; { read_json("example.json", pt); ofstream ofs("example.xml"); write_xml(ofs, pt, xml_writer_make_settings(' ', 2)); } { ifstream ifs("example.xml"); read_xml(ifs, pt); } return 0; } $ ./example terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::property_tree::xml_parser::xml_parser_error> >' what(): <unspecified file>(7): expected element name Aborted $ cat example.xml <?xml version="1.0" encoding="utf-8"?> <menu> <foo>true</foo> <bar>true</bar> <value>102.3E+06</value> <popup> <> <value>New</value> <onclick>CreateNewDoc()</onclick> </> <> <value>Open</value> <onclick>OpenDoc()</onclick> </> </popup> </menu>

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Library advice
by Mathew Benson 27 Apr '14

27 Apr '14

Is there a boost library that I can use to dynamically deserialize structures from untyped buffers? I need to write code that receives a buffer of data from another computer, with some data serialized with bitfield structs. Yes, I do understand the difficulty of doing this and that it would have been easier if the data was serialized properly before transmission. I have no control over the transmitted data, but I can get the data format defined accurately. I fully understand the numerous edge cases and pitfalls with doing this and don't take the task lightly. Therefore, I'm looking for libs and open source code to make it easier. The incoming data format can and frequently does change so I can't hard code the format, but the format is defined in an XML file. I wrote an internal database containing field type, offset, and bit lengths, and populated via the XML file. My XML file is auto generated to match the as built interface definition, bit for bit. I wrote code that deserializes most of the data, but I need to rewrite it as a general purpose function to work for all cases, including bitfield structs. For now, I can assume same CPU (little endian) and the same compiler (gcc). However, both source and destination CPUs and OS's might be 32 bit or 64 bit. In future versions, I would like to add support for endian conversion and differing compiler packing. Does boost have something that would help? Sent from my Packard Bell 386

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[Range] Extending the library for a base class and all its derived - enable_if
by Albert Yiamakis 26 Apr '14

26 Apr '14

Hello, I am looking to make a class, whose definition I cannot touch, model a Range concept. To that end I use method 2, http://www.boost.org/doc/libs/1_55_0/libs/range/doc/html/range/reference/ex… However, I am unable to specialize the relevant metafunctions (range_const_iterator, range_mutable_iterator, range_iterator) since they do not have an additional template parameter that would permit me to employ enable_if. I have found this impossible without touching either the class' definition or the metafunctions. Perhaps there is some other trick I am not aware of, in which case I would greatly appreciate hearing about it. If such a trick does not exist, then should these metafunctions feature an additional template parameter? Given that this is one of the methods to extend the library, it would make sense that one wishes to do so on conditions that enable_if can check. Albert

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