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[thread] linux.hpp, BOOST_HAS_PTHREAD_YIELD, BOOST_HAS_SCHED_YIELD
by Rob Conde 16 Oct '14

16 Oct '14

Using boost 1.55, Ubuntu 12.04, gcc 4.6 I'm building boost on linux using the lsb sdk. I was getting the failure (paraphrased): pthread_yield not declared in libs/thread/src/thread.cpp 513 The documentation for pthread_yield (http://man7.org/linux/man-pages/man3/pthread_yield.3.html) says: This call is nonstandard, but present on several other systems. Use the standardized sched_yield(2)<http://man7.org/linux/man-pages/man2/sched_yield.2.html> instead. If I change boost/config/platform/linux.hpp to define BOOST_HAS_SCHED_YIELD instead of BOOST_HAS_PTHREAD_YIELD Then sched_yield is used instead and the build finishes properly. I'm posting this for two reasons: 1. To help others running into the same issue 2. To question whether linux.hpp should be updated officially as I did above 3. If not, why Thanks, Rob Conde

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Boost.Python: Polymorphism downcasting
by Christoff Kok 16 Oct '14

16 Oct '14

Hi, I have a list of base classes in C++, I want to access them in Python as a list of their derived most classes. Is there a build in means to cater for this in Boost.Python? I've made an example the problem I ma facing: // ------------------------------- Code ----------------------------------// #include<memory> #include<iostream> #include<vector> namespace boost { template<class T> T* get_pointer(std::shared_ptr<T>& p){ return p.get(); }} struct Vehicle{ virtual ~Vehicle(){} friend bool operator==(const Vehicle& lhs, const Vehicle& rhs) { return true; }}; struct Boat: public Vehicle{ virtual ~Boat(){} friend bool operator==(const Boat& lhs, const Boat& rhs) { return true; } char const* testBoatSpecificMethod() { return "Floating."; } }; struct Truck: public Vehicle{ virtual ~Truck(){} friend bool operator==(const Truck& lhs, const Truck& rhs) { return true; } char const* testTruckSpecificMethod() { return "Trucking."; } }; class Garage { public: Garage() {}; ~Garage() {}; char const* test() { std::string temp = "Vehicle List Size: " + std::to_string(m_VehicleList.size()); return temp.c_str(); } friend bool operator==(const Garage& lhs, const Garage& rhs) { return true; } std::vector<Vehicle>& vehicleList() { return m_VehicleList; } private: std::vector<Vehicle> m_VehicleList; }; #include <boost/python.hpp> #include <boost/python/suite/indexing/vector_indexing_suite.hpp> BOOST_PYTHON_MODULE(garage_ext) { using namespace boost::python; class_<Garage>("Garage") .def("test", &Garage::test) .def("vehicleList", &Garage::vehicleList, return_internal_reference<1>()); class_<Vehicle,std::shared_ptr<Vehicle>>("Vehicle"); class_<Boat,std::shared_ptr<Boat>,bases<Vehicle>>("Boat") .def("testBoatSpecificMethod", &Boat::testBoatSpecificMethod); class_<Truck,std::shared_ptr<Truck>,bases<Vehicle>>("Truck") .def("testTruckSpecificMethod", &Truck::testTruckSpecificMethod); implicitly_convertible<std::shared_ptr<Boat>,std::shared_ptr<Vehicle>>(); implicitly_convertible<std::shared_ptr<Truck>,std::shared_ptr<Vehicle>>(); class_<std::vector<Vehicle> >("stl_vector_Vehicle") .def(vector_indexing_suite<std::vector<Vehicle> >()); } // --------------------------- Test Script -------------------------------// import garage_ext g = garage_ext.Garage() l = g.vehicleList() l.append(garage_ext.Boat()) print "Expecting a Boat object:" print str(l[0]) print g.vehicleList()[0].testBoatSpecificMethod() garage_ext.f2("Done.") // ------------------------------ Output ---------------------------------// Expecting a Boat object <garage_ext.Vehicle object at 0x7fb17a3bfb50> Traceback (most recent call last): File "test_garage.py", line 7, in <module> print g.vehicleList()[0].testBoatSpecificMethod() AttributeError: *'Vehicle' object has no attribute 'testBoatSpecificMethod'* *'Vehicle' object has no attribute 'testBoatSpecificMethod'* Here I want Vehicle to be a Boat object. If there is not a build in or recommended/known Boost.Python means to handle this problem, I'm thinking of wrapping the list (Lots of accessors to be wrapped in my library.) with a get accessor returning a boost::python::list, storing the derived most types. Getting the derived most type possibly by calling overriden 'getAsDerivedClass' method. I would like to avoid this. I dislike having to add python usage specific methods to the library, for our design and vision values / reasons. Kind Regards, Christoff

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BGL - maximum_adjacency_search - assignedVertices
by Adam Celick 14 Oct '14

14 Oct '14

I was looking at the implementation of maximum_adjacency_search algorithm and got confused by the assignedVertices local variable. It is defined as a set of vertex descriptors and is being iterated over inside the main loop (lines 168-184) but it is never inserted into. So the for loop will always skip. It looks to me as if that part of the code can be eliminated. Am I missing something? Thanks, Adam

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Generating kuratowski subgraph with external edge index map
by Amir Hassan 13 Oct '14

13 Oct '14

Hi! I have a graph which i test for planarity and in case the test fails i want to generate the kuratowski subgraph. I have code that used to compile with boost graph 1.36 but doesn't with 1.56. I guess the problem has to do with the type of the edge index map. you can find code and error messages here: http://stackoverflow.com/questions/26346343/c-boost-graph-generating-kurato… Help is greatly appreciated! greets, amir

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[interprocess 1.42] Copy multiple variables into shared memory
by Michael Behnke 13 Oct '14

13 Oct '14

Hello, I'm trying to write multiple variables one by one into a mapped_region, but somehow I fail. Here is the Code I worked on so far: boost::interprocess::shared_memory_object shm_obj(boost::interprocess::open_or_create, "Test", boost::interprocess::read_write); shm_obj.truncate(1000); boost::interprocess::mapped_region region(shm_obj, boost::interprocess::read_write, 0, 0); uint32_t size = 33; uint32_t type = 666; std::string data("I'm a Test!"); uint32_t* start_ptr_int = &(static_cast<uint32_t*> (region.get_address())[0]); std::memcpy(start_ptr_int, &size, sizeof (uint32_t)); start_ptr_int = &(static_cast<uint32_t*> (region.get_address())[4]); std::memcpy(start_ptr_int, &type, sizeof (uint32_t)); char* start_ptr_char = &(static_cast<char*> (region.get_address())[8]); std::memcpy(start_ptr_char, data.c_str(), data.length()); uint32_t sizeOfData; std::memcpy(&sizeOfData, &(static_cast<uint32_t*> (region.get_address())[0]), sizeof (uint32_t)); uint32_t typeOfData; std::memcpy(&typeOfData, &(static_cast<uint32_t*> (region.get_address())[4]), 4); char* revData = new char[sizeOfData]; std::memcpy(revData, &(static_cast<char*> (region.get_address())[sizeof (uint32_t) * 2]), sizeOfData); First I write an uint32_t into the region at index 0. Afterwards, I'm writing another uint32_t at position 4 (assuming the first uint32_t took the bytes 0 - 3). Last I write a string into the region, at index 8. Reading the first uint32_t again from shared memory works fine, as does reading the string (the last variable). But if I try to read the second variable (uint32_t) the data is not what I expected. I know that the problem is memcpy, somehow my syntax does not work. Unfortunately I could not find a matching example, cause mostly memset is used to explain the functionality of boost::mapped_region. I have to write lots of data into shared memory (structured like size1|type1|data1|...|sizeN|typeN|dataN) but still can't figure out how to do this the right way. Any suggestions are greatly appreciated. Kind regards Michael Behnke -- Bachelorand ________________________________________________________ ADITION technologies AG Schwarzwaldstraße 78b 79117 Freiburg http://www.adition.com T +49 / (0)761 / 88147 - 30 F +49 / (0)761 / 88147 - 77 SUPPORT +49 / (0)1805 - ADITION (Festnetzpreis 14 ct/min; Mobilfunkpreise maximal 42 ct/min) Eingetragen beim Amtsgericht Düsseldorf unter HRB 54076 Vorstände: Andreas Kleiser, Jörg Klekamp, Marcus Schlüter Aufsichtsratsvorsitzender: Joachim Schneidmadl UStIDNr.: DE 218 858 434

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Boost Locale – accessing ICU functions directly
by Caroline Beltran 10 Oct '14

10 Oct '14

I recently began using Boost Locale traversing and boundary analysis of Unicode strings. I’ve used some of the features available for case conversion, i.e.: to_upper(), which appears to wrap ICU’s toUpper() function. I didn’t find Boost Locale wrappers for other ICU functions such as u_isalpha() or u_isalnum(). How can I these ICU functions? Thank you!

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Are shared memory files distributable?
by Rajalakshmi Iyer 10 Oct '14

10 Oct '14

Hello, Is it possible to create a shared memory file using Boost Interprocess (with STL containers) and distribute it to several machines for reading and modifying independently? Thanks Raj -- @BlisMedia <http://twitter.com/BlisMedia> www.blismedia.com <http://blismedia.com> This email and any attachments to it may be confidential and are intended solely for the use of the individual to whom it is addressed. Any views or opinions expressed are solely those of the author and do not necessarily represent those of BlisMedia Ltd, a company registered in England and Wales with registered number 06455773. Its registered office is 3rd Floor, 101 New Cavendish St, London, W1W 6XH, United Kingdom. If you are not the intended recipient of this email, you must neither take any action based upon its contents, nor copy or show it to anyone. Please contact the sender if you believe you have received this email in error.

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[make_shared] How to use boost::make_shared with more than 9 arguments
by dariomt＠gmail.com 10 Oct '14

10 Oct '14

I could patch my local copy with several more overloads (I need up to 12 parameters) but, is there a better way? I cannot change the constructor of the class to group parameters (as recommended in StackOverflow). Of course this is for C++03 Regards

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Re: [Boost-users] Flyweight: wrapping shared_ptr
by Joaquin M Lopez Munoz 10 Oct '14

10 Oct '14

> De: Boost-users [mailto:boost-users-bounces@lists.boost.org] > En nombre de Akim Demaille > Enviado el: martes, 07 de octubre de 2014 18:27 > Para: Boost Users List > Asunto: Re: [Boost-users] Flyweight: wrapping shared_ptr > > Le 7 oct. 2014 à 18:18, Joaquín Mª López Muñoz <joaquin(a)tid.es> a écrit : > > > An alternative would be to use some sort of cloning smart pointer to > > spare the reference count, but it's not clear to me this would be > > faster than > > shared_ptr: > > > > * element exists: shared_ptr creation is slower than clone_ptr > > creation > > * element does not exist: shared_ptr creation and copy is probably > > faster than clone_ptr creation and cloning. > > Yes, indeed. A slightly smarter approach involves a cloning class that accepts a const Base& and does only clone on copy, thus avoiding dynamic memory allocation when the element already exists. This can be nicely wrapped up as follows: template<typename Base> class poly_holder { public: poly_holder(const Base& x):p(&x),dlt(false){} poly_holder(const poly_holder& x):p(x.p->clone()),dlt(true){} poly_holder& operator=(const poly_holder& x) { Base* q=x.p->clone(); if(dlt)delete p; p=q; dlt=true; return *this; } ~poly_holder(){if(dlt)delete p;} operator const Base&()const {return *p;} private: const Base* p; bool dlt; }; template<typename Base> class poly_flyweight:public boost::flyweight<poly_holder<Base>> { public: using super=boost::flyweight<poly_holder<Base>>; using super::super; const Base& operator*() const{return base();} const Base* operator->()const{return &base();} private: const Base& base()const{return this->get();} }; template<typename Base> std::size_t hash_value(const poly_flyweight<Base>& x) { return boost::hash<const Base*>()(&*x); } template<typename Base> bool operator==( const poly_flyweight<Base>& l,const poly_flyweight<Base>& r) { return static_cast<boost::flyweight<poly_holder<Base>>>(l)== static_cast<boost::flyweight<poly_holder<Base>>>(r); } template<typename Base> bool operator!=( const poly_flyweight<Base>& l,const poly_flyweight<Base>& r) { return !(l==r); } I've rewritten your test case to take advantage of this poly_flyweight thing, cleaning up some unnecessary hash and operator== overloads along the way and without resorting to the intermediate Exp_ type; see: http://coliru.stacked-crooked.com/a/76e87531b65d44f9 > Is there anyway Flyweight could have supported the operator-> natively? > It seems that with some SFINAE under the hood, it would work, don't you think? Yep, that would be possible, the only reason I didn't do it is to not clutter the interface. Also, some std classes such as (C++17) std::optional implement operator* differently, without the extra dereference required by smart pointer semantics. Joaquín M López Muñoz Telefónica

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Boost.Geometry, probable bug in point_on_surface
by Petr Doubrava 10 Oct '14

10 Oct '14

#include <boost/geometry.hpp> #include <boost/geometry/geometries/point_xy.hpp> #include <boost/geometry/geometries/polygon.hpp> void test_point_on_surface() { typedef boost::geometry::model::point<double, 2, boost::geometry::cs::cartesian> Point; boost::geometry::model::polygon<Point> poly; boost::geometry::read_wkt("POLYGON((1074699.93 703064.65, 1074702.10 703054.62, 1074704.53 703061.40, 1074703.90 703064.58, 1074699.93 703064.65))",poly); boost::geometry::correct(poly); Point point; boost::geometry::point_on_surface(poly,point); //computed point isn't on the surface of polygon //[0] 1074839.1013086310 double //[1] 703154.77900308778 double bool res = boost::geometry::within(point,poly); // res is false }

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