August 2007 - Boost-users - lists.boost.org

[boost.python] can not export a union in VC2005sp1
by qiaozhiqiang＠datangmobile.cn 10 Aug '07

10 Aug '07

// Visual V++ 2005(8.0) sp1, boost 1.34.0 // union not is_class. // because there is BOOST_STATIC_ASSERT(is_class<T>::value) in make_instance_impl // can not export union. eg, class_<union my_u> // can not return_internal_reference<> when T not is_class, eg, return char*, char&, union u& // how to write return_internal_pointer: char* get(); // how to return_value_policy<return_by_value> work: char* get() // def_readwrite(union): default get() return by value ? // is_class<T> ? T& : T get() ?? // delete BOOST_STATIC_ASSERT(is_class<T>::value); of make_instance_impl, then compile OK, and work not all OK boost/python/object/make_instance.hpp template <class T, class Holder, class Derived> struct make_instance_impl { typedef objects::instance<Holder> instance_t; template <class Arg> static inline PyObject* execute(Arg& x) { // must is_class ?? to BOOST_STATIC_ASSERT(is_class<T>::value || is_union<T>::value)?? BOOST_STATIC_ASSERT(is_class<T>::value); /////////////////////////////// #include <boost/python.hpp> using namespace boost::python; union my_u { int a; char b; char& get_ref() { return b; } char* get_ptr() { return *b; } } struct my_s { my_u u; my_u& get_ref() { return u; } my_u* get_ptr() { return &u; } }; void my_module() { //1. compile ERROR: my_u not is_class, my_u is_union, I modify one line in make_instance.hpp // BOOST_STATIC_ASSERT(is_class<T>::value) to //BOOST_STATIC_ASSERT(is_class<T>::value || is_union<T>::value) // and the def_readwrite a, b work OK. // and work OK, why not export an union? class_<my_u > u_class("my_u", init< >()); u_class.def_readwrite("a", &my_u::a); u_class.def_readwrite("b", &my_u::b); //2. compile ERROR: char not is_class, delete BOOST_STATIC_ASSERT(is_class<T>::value), but run error u_class.def("get_ref", &my_u::get_ref, return_internal_reference< >()); //3. compile ERROR: char not is_class, delete BOOST_STATIC_ASSERT(is_class<T>::value), but run error, how to return_internal_reference a char? Use def_readwrite？ u_class.def("get_ptr", &my_u::get_ptr, return_internal_reference< >()); //4. compile OK, but run ERROR, I need it return a char .def("get_value", &my_u::get_ptr, return_value_policy<return_by_value>()); //5. compile ERROR, char* is not a reference, I need but have no copy_non_const_pointer, how to write copy_non_const_pointer? u_class.def("get_copy", &my_u::get_ptr, return_value_policy<copy_non_const_reference>()); class_<my_s > s_class("my_s", init< >()); //6. compile OK, buy run ERROR: // s = my_s() // s.u.a = 100 // print s.u.a // but output s.u.a != 100 !!! // s.u.a = 100 is s.get_u().set_a(100) and get_u() not return u(is_union) by ref ? s_class.def_readwrite("u", &my_s::u); // 7. compile ERROR: my_u not is_class, is_union, modify BOOST_STATIC_ASSERT(is_class<T>::value) to // BOOST_STATIC_ASSERT(is_class<T>::value || is_union<T>::value) s_class.def("get_ptr", &my_s::get_ptr, return_internal_reference<>()); s_class.def("get_ref", &my_s::get_ref, return_value_policy<return_by_value>());//compile ok } Best 　Regards ! Qiao Zhi Qiang

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Process for adding code to boost
by Hughes, James 10 Aug '07

10 Aug '07

Hello all, I was interested in knowing how to go about presenting new code for addition to boost. I'm not talking about a new library, but extensions to existing ones. For example, I have written some code to allow serialisation of the boost::filesystem::path class (not particularly exciting or complicated, but may be useful to someone), and would like to pass it on. James This message (including any attachments) contains confidential and/or proprietary information intended only for the addressee. Any unauthorized disclosure, copying, distribution or reliance on the contents of this information is strictly prohibited and may constitute a violation of law. If you are not the intended recipient, please notify the sender immediately by responding to this e-mail, and delete the message from your system. If you have any questions about this e-mail please notify the sender immediately.

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unique sorted vector
by Michael Marcin 10 Aug '07

10 Aug '07

I have a need for a low memory set. Essentially I want an always sorted unique vector. Is such a wrapper around vector and/or deque available in Boost? Thanks, Michael Marcin

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Avoid thread locking with boost::condition
by Sam Lievesley 10 Aug '07

10 Aug '07

Hi, I am trying to avoid thread locking problems when waiting using a boost::condition pseudo code: Main thread -- Start a worker thread -- boost::mutex::scoped_lock lock(m_Mutex); m_Condition.notify_one(); Worker thread boost::mutex::scoped_lock lock(m_Mutex); while (IsAlive()) { // do some work m_Condition.wait(lock); } As we can't predict which thread gets the mutex lock first lets assume that its the main thread. If this happens then m_Condition.wait will wait indefinitely as notify was called before wait. The only reliable way (that I can see) to prevent this is to never use wait, use a timed_wait instead and a loop. Why isn't the notification signal queued in the boost::condition object? Then the order of wait / notification would not be important. thanks Sam

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Visual Studio 2005 ptr_list visualizer?
by Michael Marcin 10 Aug '07

10 Aug '07

Hello I've seen Visual Studio 2005 visualizers for various boost containers on here before. Has anyone written one for ptr_list that they can share? Thanks, Michael Marcin

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Problem with boost::bind and boost::lambda::bind
by Stefano Peluchetti 10 Aug '07

10 Aug '07

I'm a newbie to the boost library so I need some help with the following problem: Take the following code: class EaSde // Abstract class. { ... public: inline virtual double unitDiffusionInverseMap( double x ) const = 0; inline virtual void unitDiffusionInverseMap( Path& path ) const; .... }; void EaSde::unitDiffusionInverseMap( Path& path ) const { std::transform( path.values.begin(), path.values.end(), path.values.begin(), boost::bind<double>( &sde::EaSde::unitDiffusionInverseMap, this, _1 ) ); } This code works fine. However if I use boost::bind::lambda instead of boost::bind I get: 1>Compiling... 1>sdefunctionalmc.cpp 1>c:\develop\nsde\nsde\abstracteasde.hpp(58) : error C2664: 'const boost::lambda::lambda_functor<T> boost::lambda::bind<double,const sde::EaSde*,const boost::lambda::placeholder1_type>(const Arg1 &,const Arg2 &,const Arg3 &)' : cannot convert parameter 1 from 'overloaded-function' to 'const double &' 1> with 1> [ 1> T=boost::lambda::lambda_functor_base<boost::lambda::action<3,boost::lambda::function_action<3>>,boost::tuples::tuple<const double,const sde::EaSde *const ,const boost::lambda::lambda_functor<boost::lambda::placeholder<1>>,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type,boost::lambda::detail::bind_traits<boost::tuples::null_type>::type>>, 1> Arg1=double, 1> Arg2=const sde::EaSde *, 1> Arg3=const boost::lambda::placeholder1_type 1> ] 1> Reason: cannot convert from 'overloaded-function' to 'const double' 1> Context does not allow for disambiguation of overloaded function 1>c:\develop\nsde\nsde\abstracteasde.hpp(58) : error C2780: '_OutIt std::transform(_InIt1,_InIt1,_InIt2,_OutIt,_Fn2)' : expects 5 arguments - 4 provided 1> c:\programmi\microsoft visual studio 8\vc\include\algorithm(797) : see declaration of 'std::transform' Why in this case is boost::bind working and boost::lambda::bind not working? Where can I find more informations on the differences about the two? On a side note I'm wondering if I can expect different performance of the two implementations.... I'm actually moving everything to boost::lambda::bind to 1) avoid the conflict of boost::lambda::_1 and _1 2) have binders that are "lambda ready" if needed Thank you in advance for your reply.

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Using lambda for sort
by Olaf van der Spek 10 Aug '07

10 Aug '07

Hi, I'm trying to sort a map based on second, but I get all kinds of compiler errors and I have no idea what's wrong. A simple _1 > _2 works fine, but that compares the maps themselves. Also, is there a better way to write the copy from map to vector or to sort the map in general? Note that I'm using a map because I'm counting how often an integer or string occurs. #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> #include <algorithm> #include <map> #include <vector> using namespace std; using namespace boost::lambda; int _tmain(int argc, _TCHAR* argv[]) { typedef std::map<int, int> countries_t; countries_t countries; countries[0] = 5; countries[1] = 3; countries[2] = 1; typedef vector<countries_t::const_iterator> countries1_t; countries1_t countries1; for (countries_t::const_iterator i = countries.begin(); i != countries.end(); i++) countries1.push_back(i); sort(countries1.begin(), countries1.end(), _1->second > _2->second); return 0; } ------ Build started: Project: Lambda Test, Configuration: Debug Win32 ------ Compiling... Lambda Test.cpp c:\vc\temp\lambda test\lambda test.cpp(23) : error C2819: type 'boost::lambda::lambda_functor<T>' does not have an overloaded member 'operator ->' with [ T=boost::lambda::placeholder<1> ] did you intend to use '.' instead? c:\vc\temp\lambda test\lambda test.cpp(23) : error C2039: 'second' : is not a member of 'boost::lambda::lambda_functor<T>' with [ T=boost::lambda::placeholder<1> ] c:\vc\temp\lambda test\lambda test.cpp(23) : error C2819: type 'boost::lambda::lambda_functor<T>' does not have an overloaded member 'operator ->' with [ T=boost::lambda::placeholder<2> ] did you intend to use '.' instead? c:\vc\temp\lambda test\lambda test.cpp(23) : error C2039: 'second' : is not a member of 'boost::lambda::lambda_functor<T>' with [ T=boost::lambda::placeholder<2> ] c:\vc\temp\lambda test\lambda test.cpp(23) : error C2780: 'void std::sort(_RanIt,_RanIt)' : expects 2 arguments - 3 provided c:\program files\microsoft visual studio 8\vc\include\algorithm(3109) : see declaration of 'std::sort' Lambda Test - 5 error(s), 0 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

6 14

boost::variant/visitor problem
by Joe 10 Aug '07

10 Aug '07

Hi, Can someone help me. I have defined a boost::variant<long long,double,std::string> with a visitor which issues an increment. The visitor derived class below works fine for std::string and long long only within the visitor, but as soon as I add a double, I get an ambiguous call compile error (error below). I'm guessing when T within the prop_increment class is an int, the compiler doesn't know whether to use the long long version of the operator() or the double version. Does anyone know how I can get around this when I apply the visitor? Interestingly enough, if I add an int to the boost::variant template list the error goes away. ------ Compile Error ------ Error 44 error C2668: 'boost::detail::variant::make_initializer_node::apply<BaseIndexPair,Iterator>::initializer_node::initialize' : ambiguous call to overloaded function \boost\variant\variant.hpp 1273 ----------------------------- ------ Visitor Class ----------- class prop_increment : public boost::static_visitor<> { public: template <typename T, typename U> void operator()( T &, const U & ) const { return; } template<typename T> void operator()(T & lhs, const T& rhs) const { lhs += rhs; } }; ------------------------------------ boost::apply_visitor(prop_increment(),prop1,prop2); ---- Visitor Call ------------------- Thanks

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boost::iostreams::gzip_compressor and multiple files
by Robert Caldecott 10 Aug '07

10 Aug '07

I have been experimenting with the boost::iostreams to create a gzip file, for example the following works fine: using namespace boost::iostreams; filtering_ostream out; out.push(gzip_compressor()); out.push(file_sink("test.gz", std::ios::binary)); out << "This is a gz file\n"; This will create a gz file containing a single compressed file (called 'test'). I can change the name of this internal file using a gzip_params struct and all is well. However, I want to create a single gzip file that contains multiple compressed files, each with a different filename. Does anyone know how to achieve this? Thanks in advance.

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Re: [Boost-users] Serialization of hashmap
by Hansi Hansi 10 Aug '07

10 Aug '07

My system is using the dinkumware.hpp header as stdlib. There the BOOST_HAS_HASH is not set. But olso if I set this it doesn't work. Because it doesn't has the resize function and the bucket_count. Best regards Hansjörg > -----Ursprüngliche Nachricht----- > Von: boost-users(a)lists.boost.org > Gesendet: 10.08.07 08:25:39 > An: boost-users(a)lists.boost.org > Betreff: Re: [Boost-users] Serialization of hashmap > > Hansi Hansi wrote: > > > the BOOST_HAS_HASH makro wosn't set. > > OK - that macro should be set automatically by > including "config..hpp" > > I believe that I've had problem in the past in this > area. If you find out why it wasn't set, let us > know so we can fix it in the next release. > > Robert Ramaey > > > > > Best regards > > Hansjörg > > > > > > > > <hr> > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users > _________________________________________________________________________ In 5 Schritten zur eigenen Homepage. Jetzt Domain sichern und gestalten! Nur 3,99 EUR/Monat! http://www.maildomain.web.de/?mc=021114

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