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c++ Bit Fields
by Chris Gem 08 Apr '13

08 Apr '13

Please forgive me if this question has been answered but I've searched for days now and cannot find it. How do I expose a c++ struct with a bit field to python using boost::python? When I try I get this error. error: invalid pointer to bit-field ‘frameHdr_s::hdrSize’ Here is the struct: #define DATA_SIZE 0x100 typedef struct frameHdr_s { #define USE_BIT_FIELDS #ifdef USE_BIT_FIELDS // Longword 0 uint32_t hdrSize : 16; ///< Size of the header uint32_t revMin : 8; ///< Frame Minor Version uint32_t revMaj : 8; ///< Frame Major Version #else // Longword 0 uint32_t hdrSize; ///< Size of the header uint32_t revMin ; ///< Frame Minor Version uint32_t revMaj ; ///< Frame Major Version #endif } frameHdr_t; typedef struct frame_t { frameHdr_t frame_header; ///< frame header uint8_t data[DATA_SIZE]; ///< Byte array of data } frame_t; Here is boost code to expose it: using namespace boost::python; BOOST_PYTHON_MODULE(api) { class_<frameHdr_t>("frameHdr_t") .def_readwrite("hdrSize", &frameHdr_t::hdrSize) ; class_<frame_t>("frame_t") .def_readwrite("frame_header", &frame_t::frame_header) ; class_<myClass>("myClass") .def("register_callback", &myClass::register_callback) .def("boo", &myClass::boo) .def("crap", &myClass::crap) ; } I know that with ctypes I can create the same struct as in c++: from ctypes import * class frameHdr_t(Structure): _pack_ = 1 _fields_=[ # Longword 0 ("hdrSize",c_uint32, 16), ("revMin",c_uint32, 8), ("revMaj",c_uint32, 8), ] DATA_SIZE = 0x100 class frame_t(Structure): _pack_ = 1 _fields_=[ ("frame_header",frameHdr_t), ("data",c_uint8 * DATA_SIZE), ] But how do I translate from the Python version of frame_t to the c++ version of frame_t? In summary, * How do I tell boost to expose a bitfield? * If that is not possible, how do I translate from Python frame_t to C++ frame_t using boot? (I don't want to wrap in C because I need to preserve the C++ness of the interface.) The code is attached. Thank you for your time, Chris

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type_erasure question
by Aleksandar Fabijanic 08 Apr '13

08 Apr '13

Looking at the type_erasure example: typedef any<boost::mpl::vector<copy_constructible<>, typeid_<>, addable<>> > any_type; any_type x(1.1); any_type y(1); any_type z(x + y); Apparently, without placeholders for x and y, this is undefined behavior. Am I interpreting it right? If so, shouldn't it fail to compile or at least throw an exception at runtime? Thanks, Alex

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publish/subscribe/message architecture using boost
by Sean Farrow 07 Apr '13

07 Apr '13

Hi all, I 'm currently looking at redesigning an application and changing to boost/c++11 library components. The application reads data from an input, processes the data and then send it to an output. The current architecture is one thread per "device" where a device is a pair of input/output ports and one processing stage. What I'd like to do is move this to either a publish/subscribe model or some form of message-based system where an input comes in and a message is then sent to the next stage of the process. All stages will happen on the same physical/virtual machine. Are there any good pub/subscribe or message-based components using the boost architecture that works on mac osx/win32. Any help appreciated. Regards Sean.

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Re: [Boost-users] [boost][thread] Future returning 0xfeeefeee
by Stefan Strasser 07 Apr '13

07 Apr '13

Zitat von Klaim - Joël Lamotte <mjklaim(a)gmail.com>: > My current suspicion: maybe I do something wrong with the lifetime of the > promise? > I don't see what unfortunately. your example is not easy to read. IIUC, after execute(), the work queue is emptied and the last shared_ptr to struct K goes out of scope. K contains your promise and the future associated with it is accessed after the promise has been destroyed. try a breakpoint in the destructor of K to make sure, I don't have tbb installed to test.

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[boost][thread] Future returning 0xfeeefeee
by Klaim - Joël Lamotte 07 Apr '13

07 Apr '13

I'm stuck with a problem I quite don't understand and that involve either boost::future/promise or tbb::concurrent_queue, or my understanding of using both. I think there is a high probability that someone here will point to the problem, but I will report too to the tbb forum Some context: - I'm using VS2012 Update 2 - it's 32 bit DEBUG mode - I use Boost.Thread V4 (in CMake I set "add_definitions( -DBOOST_THREAD_VERSION=4 )" to force it ) - I use TBB 4.1 Update 2 I've setup a test (using GTest) which reproduce the problem: ############ int TRUC = 42; TEST( Test_WorkQueue, future_promise_shared_work ) { WorkQueue work_queue; // I'm doing this like that because it reflect the use case I have, // I didn't find another way to have the promise alive in a container which don't allow move semantic auto do_some_work = [&]()-> boost::future<int*> { struct K { boost::promise<int*> promise; void foo() { promise.set_value( &TRUC ); } }; auto object_ptr = std::make_shared<K>(); // D: work_queue.push( [=] { object_ptr->foo(); }); return object_ptr->promise.get_future(); }; auto ft_value = do_some_work(); work_queue.execute(); auto value = ft_value.get(); ASSERT_EQ( &TRUC, value ); // this fails, value == 0xfeeefeee } ########## My WorkQueue type use tbb::concurrent_queue and is defined as: ########## class WorkQueue { public: template< class WorkTask > void push( WorkTask&& task ) { m_task_queue.push( std::forward<WorkTask>( task ) ); } /** Execute all the work queued until now. */ void execute() { if( m_task_queue.empty() ) return; bool end_of_work = false; m_task_queue.push( [&]{ end_of_work = true; } ); std::function<void()> work; while( !end_of_work && m_task_queue.try_pop( work ) ) { work(); } } private: mutable tbb::concurrent_queue< std::function<void()> > m_task_queue; }; ############ It's basically a simple wrapper around the concurrent_queue, but maybe the execute() code have an impact. THE PROBLEM: The test fails. value == 0xfeeefeee as soon as the get() call is done. Using the debugger, I can't figure where the data is lost. It seem that everything is correct until when all the hierarchy of function call returns the result...which is different and wrong once out of the function. I first wrote this test with std::vector< std::function<void()> > instead of the concurrent queue to check if it was boost::future/promise which was not working well with Boost.Thread V4. With the vector instead of concurrent_queue, the code works perfectly. Does someone have an idea what is going on? Joel Lamotte

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Re: [Boost-users] Boost-users] publish/subscribe/message architecture using boost
by Brian Wood 06 Apr '13

06 Apr '13

Sean Farrow writes: > Hi all, > I''m currently looking at redesigning an application and changing to > boost/c++11 library components. The application reads data from an input, > processes the data and then send it to an output. The C++ Middelware Writer (CMW) may be of interest. The application you mention sounds similar to the middle tier of the CMW -- http://webEbenezer.net/build_integration.html http://webEbenezer.net/misc/cmwAmbassador.hh http://webEbenezer.net/misc/cmwAmbassador.cc > The current architecture is one thread per "device" where a device is a > pair of input/output ports and one processing stage. What I'd like to > do is move this to either a publish/subscribe model or some form of > message-based system where an input comes in and a message is then > sent to the next stage of the process. All stages will happen on the same > physical/virtual machine. Are there any good pub/subscribe or > message-based components using the boost architecture that works > on mac osx/win32. We don't have pub/subscribe support, but the CMW is a message-based middleware. -- Brian Wood Ebenezer Enterprises - in G-d we trust. http://webEbenezer.net (651) 251-9384

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Scope Tracer or General Scope Function with parameter or variable values
by Anlin Zhang 05 Apr '13

05 Apr '13

Hi, I'm wondering if a "Scope Tracer" or a "General Scope Function" can be easily implemented with existing boost libraries now. One example use case is to log variable or parameter values or any program state when entering or leaving a scope, but it can do more than just logging, it can, for example, lock/unlock mutex, or prepare/teardown test cases, etc. For logging requirement, to give you an idea, the expected log message looks like this: >04/10/09 05:29:12:210257 entering func foo with parameter a=10, b=1.5, d.x=10, d.y=[string], global d=2, filename:test.cpp>04/10/09 05:29:12:210257 entering while() a=10, b=1.5, d.x=10>04/10/09 05:29:12:210257 leaving while() a=9, b=1.5, d.x=9>04/10/09 05:29:12:210257 entering while() a=9, b=1.5, d.x=9>04/10/09 05:29:12:210257 leaving while() a=8, b=1.5, d.x=8>...>04/10/09 05:29:12:210257 entering while() a=2, b=1.5, d.x=2>04/10/09 05:29:12:210257 leaving while() a=1, b=1.5, d.x=1>04/10/09 05:29:12:210257 entering while() a=1, b=1.5, d.x=1>04/10/09 05:29:12:210257 leaving while() a=0, b=1.5, d.x=0>04/10/09 05:29:12:210257 leaving function foo with parameter a=0, b=1.5, d.x=0, d.y=[string], global d=2, filename:test.cpp It does not have to be logging, it can do any general processing when entering/leaving a scope. I implemented a small library to do so in 2008 mainly for tracing, it worked fine for me and I never revisited it again until recently. Wondering if boost has libraries to support such a requirment. My implementation has a template class logger_class which can manage the log-level at runtime and send the log message to standard-output or other places. Application code use a macro to invoke the library, the macro can be disabled at compile time, or weakened to only log scope without variables. Example of the macro definition: #ifdef ENABLE_ONLY_SCOPE_TRACER #define SCOPE_TRACER(logger_class, logger, args, level, scope) \ scope_tracer<logger_class> tracer_obj(logger, __FUNCTION__, __FILE__, __LINE__); \ if (logger.get_level() >= level){ \ tracer_obj.init(level, scope).noMore(); \ } #else #ifdef DISABLE_SCOPE_VAR_TRACER #define SCOPE_TRACER(logger_class, logger, args, level, scope) #else #define SCOPE_TRACER(logger_class, logger, args, level, scope) \ scope_tracer<loggerClass> tracer_obj(logger, __FUNCTION__, __FILE__, __LINE__); \ if (logger.get_level() >= level){ \ tracer_obj.init(level, scope) << args; \ tracer_obj.noMore(); \ } #endif#endif Application code example: int globalVar; void MyClass::func1( A a, B&b, C* c, int d, std::string & s){ SCOPE_TRACER(MyLogger, test_logger, a<<b<<c<<d<<s<<globalVar, LOG_LEVEL_TRACE, "func1"); ... int localVar; while(x){ SCOPE_TRACER(MyLogger, test_logger, x<<a<<b<<c<<d<<s<<globalVar<<localVar, LOG_LEVEL_TRACE, "while(x)"); ... } ... } As you see, "<<" operator is being used. But it does not have to be only "<<" operator. Basically any C++ operator can be supported between the logger class and logged type. And the logger_class is not limited to just do tracing, it can virtuall do anything. I can attach the code if needed. The code was compiled with GCC on linux and VisualStudio on Windows. If the above functionality can be easily achieved using existing boot library, please advise how. Otherwise is it worth to request such a feature in boost? Thanks,Anlin

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Visual C++ 11 cannot find Boost unit_test_framework library in CMake generated project
by Emre Şahin 05 Apr '13

05 Apr '13

I have a C++ project using CMake and Boost that compiles/links under Linux without any problems. I'm working towards porting this to Windows via Visual C++ 2012. My CMake configuration is as follows: set(BOOST_ROOT ${DEPENDENCY_DIR}/boost/) set(Boost_USE_STATIC_LIBS ON) set(Boost_USE_MULTITHREADED ON) set(Boost_USE_STATIC_RUNTIME OFF) find_package(Boost 1.53 COMPONENTS system date_time chrono serialization filesystem program_options random thread regex unit_test_framework) message(STATUS "Boost Version:" ${Boost_VERSION}) message(STATUS "Boost Include Dirs:" ${Boost_INCLUDE_DIR}) message(STATUS "Boost Libraries:") foreach(lib ${Boost_LIBRARIES}) message(STATUS ${lib}) endforeach() include_directories(${Boost_INCLUDE_DIR}) and I'm using `target_link_libraries` with `${Boost_LIBRARIES}` in my targets. Also above `message` commands show all found files without any problem. Moreover required libraries show `libboost_unit_test_framework-vc110-mt-gd-1_53.lib` as it should be. (Screenshot: http://i.stack.imgur.com/UgPTG.png) However, when I build one of the targets, I get 2>LINK : fatal error LNK1104: cannot open file 'boost_unit_test_framework-vc110-mt-gd-1_53.lib' I removed another Boost library and from the error it seems the linker is able to find others. (like `chrono` or `serialization`.) But the error message is a bit different. The filename has _lib_ in front of it. 2>LINK : fatal error LNK1104: cannot open file 'libboost_serialization-vc110-mt-gd-1_53.lib' Why does VC++ looks for a file prefixed with **boost** and not **libboost** for unit_test_framework? Best Regards, Emre PS: This is crossposted to http://stackoverflow.com/questions/15815467/ if you like to answer there.

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Boost-enabled loosely coupled ORM serialization
by Michael Powell 05 Apr '13

05 Apr '13

Hello, I am coming up on a decision in the architecture I am working on. I want to serialize some domain data to a data store. I'm aware boost has serialization features, which I'd like to explore further. I'm coming at this first from a boost standpoint because I am successfully building upon it for other parts of the engine and domain model, so boost is available right now. I am expecting I might go with a third-party library like ODB, Wt::Dbo, or something like that. Also, background, I am no stranger to ORM concepts. I was first exposed to them through Java, C# .NET, and have dealt with Hibernate, NHibernate, Fluent NHibernate, and so on. So vocabulary-wise, grammar-wise, we're talking the same language. Also, I'll defer backend decisions until later. Probably that will be somewhat determined by target platform support and so on: landing on ArchLinux ARM. For now, my focus for now is on keeping ORM intersection with my domain as loosely coupled as possible. For anyone versed in ORM nuances, for obvious reasons, I want for the ORM to be as transparent through the domain model as possible. I want to steer clear of the active record anti-pattern whenever possible. I'd like to gear up for a repository pattern whenever feasible. No time to get into that discussion why I believe these are patterns or anti-patterns. That's a separate blog for another time. Wrappers like smart pointers, smart collections, are understandable, and may be the way to go, but put opaqueness layers between end-users of the domain objects and the rest of the model. Will use them if I must, but I'd like to avoid them if possible. Additionally, given some language "features", perhaps "limitations" if you will, of C++11, as contrasted with a C# let's say, I also want for any ORM code, whether meta-programmed or not, to be as non-intrusive to the domain model as possible. I've seen a ton of code that have persist methods, friend access, macros, and such. Sounds like a tall order I know. Call me spoiled on the "niceness" of .NET, Reflection, and so on. More likely I'm getting reacquainted with the practicalities of using a paradigm-rich language like C++11. Now back to the "real world" what the rest of us deal with. Realistically, a sober look at it, I believe there will be tradeoffs: SOLID is my goal, sufficiently extensible to meet the seams we'll need to meet, yet maintainable at the end of the day. Regards, Michael Powell

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Signals2 event broker framework
by Michael Powell 05 Apr '13

05 Apr '13

Hello, I am interested to put an event broker system into practice in our architecture. Since we're using boost successfully already, Signals2 seems like the most likely candidate. At the moment, this is intra-process, most likely inter-thread but for now that's not the concern. Just getting event signals from point A to points B, C, D in pub/sub manner, however, is. http://www.boost.org/doc/libs/1_53_0/doc/html/signals2.html If I can abstract that out further, for instance I noticed there was an C# event-like abstraction someone published as an add-on feature to boost a little while back, handled subscriptions through +=, -= operator overloads, that sort of thing, would be helpful, but probably not completely necessary. If I can loosely couple subscribers from publishers is also desired. Something like bbv EventBroker ( http://code.google.com/p/bbvcommon/wiki/EventBroker) is to C#. That'll keep things nice and loosely coupled, so that if we ever need to get more distributed (i.e. via a CORBA or ZeroC) we can potentially do so. Regards, Michael Powell

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