- Boost-users - lists.boost.org

fusion result_of::at<Seq, N>::type doesn't return the type I expect
by Hicham Mouline 23 Feb '10

23 Feb '10

Hi, This code prints double and 0 where I would expect is_same to print 1. msvc2008, boost trunk #include <iostream> #include <boost/type_traits/is_same.hpp> #include <boost/mpl/range_c.hpp> #include <boost/mpl/distance.hpp> #include <boost/mpl/vector.hpp> #include <boost/mpl/find.hpp> #include <boost/fusion/include/mpl.hpp> #include <boost/fusion/include/size.hpp> #include <boost/fusion/include/at.hpp> #include <boost/fusion/include/for_each.hpp> #include <boost/fusion/include/adapt_struct.hpp> struct p { double f0; double f1; double f2; unsigned int f3; unsigned int f4; unsigned int f5; unsigned int f6; }; /// macro required to be at global namespace BOOST_FUSION_ADAPT_STRUCT( p, (double, f0) (double, f1) (double, f2) (unsigned int, f3) (unsigned int, f4) (unsigned int, f5) (unsigned int, f6) ) typedef boost::mpl::vector<double, unsigned int> dtt; typedef boost::fusion::result_of::at_c<p,0>::type t0; int main() { std::cout<< typeid(t0).name() <<std::endl; std::cout<< boost::is_same< t0, double >::value <<std::endl; return 0; } I am certain I am missing something obvious, rds,

1 0

shared_ptr and polymorphism
by Abderrahmane Madani 23 Feb '10

23 Feb '10

Just a little problem that I can't fix. Suppose that I have these four classes class B {}; class D1: public B {}; class D2: public B {}; class E: public D1 {}; this test: void foo(D1 *) {} void foo(D2 *) {} int main() { E *e = new E; foo(e); return 0; } work just fine but this one void foo(shared_ptr<D1>) {} void foo(shared_ptr<D2>) {} int main() { shared_ptr<E> e(new E); foo(e); return 0; } the compiler say that the foo(boost::shared_ptr<E>&)' is ambiguous. Please, can someone help me to understand why and how can I fix this problem without changing the functions name. Thanks Boost 1.35 GCC 4.4.1 regards

2 1

[filesystem] wpath and fopen() on windows
by Paul 23 Feb '10

23 Feb '10

Hi, What is the best way for me to use boost::filesystem::wpath with a 3rd party C library that expects a const char* filename, on Windows? On linux, its simple: my_file.to_external_string() but on windows that gives me a wide-character string. So far the only thing I can think of is to roll my own wstring --> UTF8 conversion function, but I'm not even sure that is correct (will fopen() work with UTF-8 encoded filenames on windows?). thanks, Paul

2 5

Optional XML serialization
by Paul 23 Feb '10

23 Feb '10

Hi, I use xml_woarchive and xml_wiarchive for reading/writing configuration files. It seems work work well for me, but now I'd like to see if I can do more with it... is it possible to load an XML serialized file, but completely IGNORE a subtree of the XML file if desired? eg template <class Archive> void load( Archive & ar, MyConfig & c, const unsigned int version ) { ar >> make_nvp("standard",c.standard); if (some_global_flag_or_whatever) ar >> make_nvp("advanced", c.advanced); else ar.skip("advanced"); // key bit } The motivation is that I want to "register modules" (in my app) that can read/write their configuration in an XML configuration file. But if the module is not registered, I want to skip that part of the configuration file and move on. I figure since the XML format is like a tree, it might/should be possible to ignore an entire segment of the tree. Is it possible? In a related note, the "class_id" bits in xml archives seems to make it difficult for users to hand-edit the XML file... Are these tags required? thanks, Paul

3 8

asio newbie: picking a free port number
by Avi Bahra 23 Feb '10

23 Feb '10

I am writing a simple client/server program which will only run on Unix boxes (linux, HP-UX, AIX). By manually choosing the port number,everything works ok. Whenever I get an "Address in use" i choose a different number. I want to free clients of this program from having to do this. >From googling around it appears that there is way of the OS, to pick a free port number. i.e by binding to port 0, sock.bind(('', 0))/ sock.getsockname()[1] Is there any boost:asio recommended way of doing this ? Is there any way of completely abstracting out the use of port numbers from an end users perspective using boost asio ? i.e so that client/server agree on a free port number behind the scenes. Any help appreciated. Best regards, Ta, Avi

2 1

[mpl] bind help sought
by Manfred Doudar 23 Feb '10

23 Feb '10

Hi, I need to be explicit about a function call, but unsure quite how to make it work, cut down example follows: struct M { static void foo() { ... } }; struct R { static void foo() { ... } }; struct Func { typedef void result_type; template <typename T, typename U> result_type operator()(U& u) const { T::foo(); // call on either M or R // do something with 'u' } }; int main(int argc, char** argv) { using namespace boost::mpl; typedef vector<M, R> vec; Func f; Object instance; for_each<vec>(boost::bind(&Func::operator()<XXX, Object>, boost::ref(f), instance) ); return 0; } Question is, what goes in at XXX above? I was thinking something along the lines of: boost::mpl::bind<boost::mpl::_1> ..but well, that doesn't work. All help appreciated. Cheers, -- Manfred

3 4

[proto] Problem using BOOST_PROTO_AUTO
by Manjunath Kudlur 23 Feb '10

23 Feb '10

I have the following program to print out the arguments of a function call expression. It works fine when I directly call the grammar on the expression like so : foo_tostr()(f(a,b,c)). However, if I assign the expression to a variable pr using BOOST_PROTO_AUTO and call foo_tostr()(pr), I get error of the form "conversion from ‘boost::fusion::... to non-scalar type .... requested". Can someone let me know what I am doing wrong? #include <iostream> #include <boost/proto/proto.hpp> #include <boost/proto/proto_typeof.hpp> #include <sstream> #include <string> using namespace std; namespace proto = boost::proto; unsigned ids; struct var { unsigned id; var() { id = ++ids; } }; struct foo {}; typedef proto::terminal<var>::type Var; typedef proto::terminal<foo>::type Foo; struct _var_tostr : proto::callable { typedef string result_type; result_type operator()(var const &v) const { stringstream sout; sout << "v" << v.id << " "; return sout.str(); } result_type operator()(foo const &v) const { stringstream sout; sout << "foo("; return sout.str(); } }; struct var_tostr : proto::or_< proto::when<proto::terminal<var>, _var_tostr(proto::_value)> > {}; struct str_plus : std::plus<std::string>, proto::callable {}; struct foo_tostr : proto::or_ < proto::when<proto::function<proto::terminal<foo>, proto::vararg<proto::terminal<var> > >, proto::fold<proto::functional::pop_front(proto::_expr), string(), str_plus(proto::_state, var_tostr)> > > {}; int main() { Var a, b, c; Foo f; #define COPY_AND_PRINT #ifdef COPY_AND_PRINT BOOST_PROTO_AUTO(pr, (f(a,b,c))); cout << foo_tostr()(pr) << endl; #else cout << foo_tostr()(f(a,b,c)) << endl; #endif } -- Manjunath

2 1

[proto] vararg expressions to string
by Manjunath Kudlur 23 Feb '10

23 Feb '10

I am trying understand the use of proto::fold to handle vararg expressions. As an experiment, I am trying to convert expressions of the form foo(a,b,c) to a string of the form "foo(a,b,c)". I currently have the following code where I treat the vararg expression as a fusion sequence and convert each parameter to a string using appropriate grammar. In the operator() of _foo_tostr, I have a case for each length of the vararg expression. Please let me know if there are better ways of doing this. #include <iostream> #include <boost/proto/proto.hpp> #include <boost/fusion/container/list/cons.hpp> #include <boost/fusion/include/cons.hpp> #include <boost/fusion/include/transform.hpp> #include <sstream> #include <string> using namespace std; namespace proto = boost::proto; namespace fusion = boost::fusion; unsigned ids; struct var { unsigned id; var() { id = ++ids; } }; struct foo {}; typedef proto::terminal<var>::type Var; typedef proto::terminal<foo>::type Foo; struct _var_tostr : proto::callable { typedef string result_type; result_type operator()(var const &v) const { stringstream sout; sout << "v" << v.id; return sout.str(); } }; struct var_tostr : proto::or_< proto::when<proto::terminal<var>, _var_tostr(proto::_value)> > {}; struct _foo_tostr : proto::callable { typedef string result_type; template<typename T> result_type operator()(T const &e) const { stringstream sout; sout << "foo("; if(fusion::size(e) == 1) { sout << ")"; } else if(fusion::size(e) == 2) { sout << var_tostr()(fusion::at_c<1>(e)) << ")"; } else if(fusion::size(e) == 3) { sout << var_tostr()(fusion::at_c<1>(e)) << ", " << var_tostr()(fusion::at_c<2>(e)) << ")"; } else if(fusion::size(e) == 4) { sout << var_tostr()(fusion::at_c<1>(e)) << ", " << var_tostr()(fusion::at_c<2>(e)) << ", " << var_tostr()(fusion::at_c<3>(e)) << ")"; } return sout.str(); } }; struct foo_tostr : proto::or_ < proto::when<proto::function<proto::terminal<foo>, proto::vararg<proto::terminal<var> > >, _foo_tostr(proto::_expr)> > {}; int main() { Var a, b, c; Foo f; cout << foo_tostr()(f(a,b,c)) << endl; }

2 1

Re: [Boost-users] [serialization] Polymorphic serialization with polymorphic archives problem...
by Bogdan 23 Feb '10

23 Feb '10

> Hi, > I have the same scenario, and it's not a problem. > If i understand (my english is poor, sorry) well. > But there is differences: > - I use GCC compilers (but boost is portable). > - I use static linking. > Probably this differences should not have consequences on the result. > I didn't read your code... Had you follow this rules ? > - Register child class (a simple way is using the > BOOST_CLASS_EXPORT macro). > - In the serialize method of your child class, call the > serialization of parent's class (optional). I use > BOOST_SERIALIZATION_BASE_OBJECT's macro. > > If you register child class it should be ok... > Regards, > Damien. > > Hi Damien, My reply has not been posted in gmane so I try again: Thank you for your quick reply. I believe I followed the rules: 1. polymorphic_derived1 and polymorphic_derived2 do include the serialization of the base class via "ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP(polymorphic_base); " 2. there is no usage of BOOST_CLASS_EXPORT ( and there shouldn't be any: according to the documentation, in a dll setup one must declare BOOST_CLASS_EXPORT_KEY in the headers containing the classes to be serialized and BOOST_CLASS_EXPORT_IMPLEMENT in the .cpp files). In my example, there are exactly three declarations of BOOST_CLASS_EXPORT_KEY: one in polymorphic_base.hpp, and two in polymorphic_derived2.hpp one for polymorphic_derived1 and another for polymorphic_derived2. Similarly, there are only three usages of BOOST_CLASS_EXPORT_IMPLEMENT. 3. for deeper hierarchies where every class can be potentially serialized, one should probably register all the classes and not just the most derived children. I have the feeling that the type of deployment (dll vs exe) is the crux of the problem. For that, I created four different scenarios with the same source files and I got the following results: 1. all files in one exe with the serialization library linked statically - WORKS AS EXPECTED. 2. all files in one exe with the serialization library linked as a dll - WORKS AS EXPECTED. 3. serialization files in a separate dll. Both the main executable and my dll link with the dll version of the serialization library: main.exe my_serialization.dll boost_serialization.dll my_serialization.dll boost_serialization.dll Builds OK but FAILS at runtime , at run time I get a C++ exception BEFORE main() in basic_serializer_map.cpp around the line 48: 'archive_exception::multiple_code_instantiation with the message "code instantiated in more than one module - polymorphic_base"' 4. serialization files in a separate dll. Both the main executable and my dll link with the static version of the serialization library: main.exe my_serialization.dll boost_serialization.lib my_serialization.dll boost_serialization.lib Builds OK but FAILS at runtime while trying to serialize with the following exception thrown in oserializer.hpp(line 424):struct polymorphic::save(): 'unregistered void cast class polymorphic_derived1<-polymorphic_base in function 'int __cdecl main(int,char *[])'' The source code in the scenarios above is identical with the exception of dllexport/dllimport declaration needed for dlls. Whenever the serialization code is relegated to a different library it seems there are problems with boost serialization: - if boost is linked as a static lib into a user dll, the class serializers do not get registered at all with their associated map singleton. - if boost is linked as a dynamic lib into a user dll, the class serializers register twice with the map singleton of the polymorphic base archive. I don't want to add them here but I can provide any of the projects above to those interested. Thank you all, Bogdan

2 1

Re: [Boost-users] Foreach For iterating two containers
by Rusty Jones 23 Feb '10

23 Feb '10

I agree that a built-in solution to FOREACH would be best, but a secondary choice would be to use a zip iterator. http://www.boost.org/doc/libs/1_42_0/libs/iterator/doc/zip_iterator.html Cheers, Rusty

3 2