April 2011 - Boost-users - lists.preview.boost.org

Floyd-Warshall Example
by GOO Creations 15 Apr '11

15 Apr '11

Hi all I'm trying to figure out how to use the Floyd-Warshall algorithm. It seems like there is no example (like with the other algorithms); can someone maybe point me to an example. I'm having problems with the parameters, especially with the DistanceMatrix. Thank you Chris

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[boost::iostreams] Is it possible to take char_type other than char or wchar_t
by 甜瓜 15 Apr '11

15 Apr '11

Hi, all, I have a proposal to make boost::iostreams support char_type other than char or wchar_t. Since the library gives users the opportunity to define char_type in Device, it should be available to boost::iostreams::copy from any source to any sink with the *same* char_type. Eg, If both Devices have UserDefinedStructure as char_type, boost::iostreams::copy should copy UserDefinedStructure objects from source to sink and return the number of objects copied. Currently, it is forbidden by a mistake (or not?) in boost::iostreams::copy. That is "detail::basic_buffer<char_type>" only allocate the raw space without construct them by using UserDefinedStructure constructor. I really appreciate this library, so would boost::iostreams please to concider my proposal? Or there are other ways to achieve this? Thank you in advance. -- leishen

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boost.parameter - best practices
by Christoph Heindl 15 Apr '11

15 Apr '11

Hi, I have a set of classes that offer named parameter enabled constructors through the use of argument packs. Currently I have one huge header container all the available arguments of all classes. // params.h namespace geo { namespace keywords { BOOST_PARAMETER_NAME(a) BOOST_PARAMETER_NAME(b) } } // thing.h namespace geo { class thing { public: template<class Opts> thing(const Opts &o) { _m_x = o[Keywords::_a | 10]; //etc.. } }; } // thing2.h namespace geo { class thing2 { public: template<class Opts> thing2(const Opts &o) { _m_x = o[Keywords::_b | 10]; //etc.. } }; } First question: I'd like to place the BOOST_PARAMETER_NAME keywords as close to its usage as possible. I.e. I'd like to place BOOST_PARAMETER_NAME(a) on top of thing.h. If I do so, I think that over time other classes will start to have their own BOOST_PARAMETER_NAME(a) constructs in their header files, which I think would lead to multiple defined symbols if two class headers are included in the same translation unit, correct? So, is their any way to declare a parameter inside a class, through a typedef or similar? Let me illustrate class x { public: typedef boost::parameter::keyword<...> a; template<class Opts> x(const Opts &o) { _m_x = o[a | 10]; } }; x my_x(x::a = 5); If that is not possible, is there any way to limit the template parameter Opts in the above example to set of possible parameters? Best regards, Christoph

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[Preprocessor] MSVC, File Iteration, and FLAGS()
by Robert Rumpf 14 Apr '11

14 Apr '11

I’ve reduced my problem to the following code snippet which compiles fine on GCC, but which fails to compile on MSVC (versions 9 and 10). The error provided by MSVC is “fatal error C1012: unmatched parenthesis : missing ')'”. It seems to have to do with the BOOST_PP_ITERATION_FLAGS() directive. I’m using Boost 1.45.0. Any thoughts on workarounds or bug-fixes? Thanks, Rob Rumpf *#if* !BOOST_PP_IS_ITERATING *# ifndef* __FILE_HPP__ *# define* __FILE_HPP__ *# include* <boost/preprocessor/iteration/iterate.hpp> *# include* <boost/preprocessor/seq/size.hpp> *# include* <boost/preprocessor/arithmetic/dec.hpp> /// Set up the first (most outer) nested FOR loop. *# define* INDICES_1 (A)(B) /// Set up the second (middle) nested FOR loop. *# define* INDICES_2 (C)(D) /// Set up the third (inner) nested FOR loop (1 of 3). *# define* INDICES_3a (E)(F) /// Set up the third (inner) nested FOR loop (2 of 3). *# define* INDICES_3b (G)(H) /// Set up the third (inner) nested FOR loop (3 of 3). *# define* INDICES_3c (I)(J) // Set up the number of iterations (see the Boost.Preprocessor library). // Set up the filename to be called (which is this one, see the Boost.Preprocessor library). *# define* BOOST_PP_ITERATION_PARAMS_1 (3, (0, BOOST_PP_DEC(BOOST_PP_SEQ_SIZE(INDICES_1)), "file.hpp")) // Iterate (see the Boost.Preprocessor library) on the first (most outer) nested FOR loop. *# include* BOOST_PP_ITERATE() *# endif* // __FILE_HPP__ // Choose the first iteration. *#elif* BOOST_PP_ITERATION_DEPTH() == 1 // Set up the number of iterations (see the Boost.Preprocessor library). // Set up the filename to be called (which is this one, see the Boost.Preprocessor library). *# define* BOOST_PP_ITERATION_PARAMS_2 (3, (0, BOOST_PP_DEC(BOOST_PP_SEQ_SIZE(INDICES_2)), "file.hpp")) // Iterate (see the Boost.Preprocessor library) on the second (middle) nested FOR loop. *# include* BOOST_PP_ITERATE() // Choose the second iteration. *#elif* BOOST_PP_ITERATION_DEPTH() == 2 // Set up the number of iterations (see the Boost.Preprocessor library). // Set up the filename to be called (which is this one, see the Boost.Preprocessor library). *# define* BOOST_PP_ITERATION_PARAMS_3 (4, (0, BOOST_PP_DEC(BOOST_PP_SEQ_SIZE(INDICES_3a)), "file.hpp", 0)) // Iterate (see the Boost.Preprocessor library) on the third (inner) nested FOR loop (1 of 3). *# include* BOOST_PP_ITERATE() // Set up the number of iterations (see the Boost.Preprocessor library). // Set up the filename to be called (which is this one, see the Boost.Preprocessor library). *# define* BOOST_PP_ITERATION_PARAMS_3 (4, (0, BOOST_PP_DEC(BOOST_PP_SEQ_SIZE(INDICES_3b)), "file.hpp", 1)) // Iterate (see the Boost.Preprocessor library) on the third (inner) nested FOR loop (2 of 3). *# include* BOOST_PP_ITERATE() // Set up the number of iterations (see the Boost.Preprocessor library). // Set up the filename to be called (which is this one, see the Boost.Preprocessor library). *# define* BOOST_PP_ITERATION_PARAMS_3 (4, (0, BOOST_PP_DEC(BOOST_PP_SEQ_SIZE(INDICES_3c)), "file.hpp", 2)) // Iterate (see the Boost.Preprocessor library) on the third (inner) nested FOR loop (3 of 3). *# include* BOOST_PP_ITERATE() // Look for the third nested loop, but index over INDICES_3a this time. *#elif* BOOST_PP_ITERATION_DEPTH() == 3 && BOOST_PP_ITERATION_FLAGS() == 0 // Look for the third nested loop, but index over INDICES_3b this time. *#elif* BOOST_PP_ITERATION_DEPTH() == 3 && BOOST_PP_ITERATION_FLAGS() == 1 // Look for the third nested loop, but index over INDICES_3c this time. *#elif* BOOST_PP_ITERATION_DEPTH() == 3 && BOOST_PP_ITERATION_FLAGS() == 2 *#endif* // BOOST_PP_IS_ITERATING

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[boost::threads] -D_REENTRANT?
by Panagiotis Foteinos 14 Apr '11

14 Apr '11

Hello users. I am using boost::threads for an application that allocates space in heap with the new operator. Therefore, different threads allocate memory in parallel. Do I have to link my application to any other library apart from the libboost_thread to guarantee a thread safe memory allocation? I searched online, but I got more confused. Do I have to define the -D_REENTRANT or the -pthread symbol? Best Regards, Panagiotis Foteinos

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Boost::bind member function and save to function pointer
by David McCallum 14 Apr '11

14 Apr '11

I'd like to implement an event-handling scheme that supports member functions. For example, I would have a class that accepts a function pointer, stores it, and calls that function when some event occurs. I'd like to be able to store a pointer to a member function with boost::bind(): void staticReceiver(std::string message) { cout << message << endl; }//staticReceiver void ChatClient::memberReceiver(std::string message) { cout << message << endl; }//testReceiver void ChatClient::testBind(void) { void (*funcPointer)(std::string message); boost::bind(&ChatClient::memberReceiver, this, _1)("Bind works"); funcPointer = staticReceiver; (*funcPointer) ("Function pointer works"); //##### THIS LINE WILL NOT COMPILE ##### funcPointer = boost::bind(&ChatClient::memberReceiver, this, _1); }//testBind However, I get the following compiler error: g++ -DHAVE_CONFIG_H -I. -I./libdasyne/lowlevel -I/opt/boost/include -D_REENTRANT -Wall -g -O2 -MT ChatClient.o -MD -MP -MF .deps/ChatClient.Tpo -c -o ChatClient.o `test -f 'examples/ChatClient.cpp' || echo './'`examples/ChatClient.cpp examples/ChatClient.cpp: In member function ‘void ChatClient::testBind()’: examples/ChatClient.cpp:56: error: cannot convert ‘boost::_bi::bind_t<void, boost::_mfi::mf1<void, ChatClient, std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, boost::_bi::list2<boost::_bi::value<ChatClient*>, boost::arg<1> > >’ to ‘void (*)(std::string)’ in assignment make: *** [ChatClient.o] Error 1 Can it be done? Thanks in advance.

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[phoenix] v2 to v3 transition of extension mechanism
by alfC 14 Apr '11

14 Apr '11

Hi, I am updating some of my code to use Phoenix3 instead of Phoenix2. For example in Phoenix2 I used to have this extension to support 'cos(...)' expressions: namespace boost{ namespace phoenix{ struct cos_eval{ template<class Env, typename Arg_> struct result{typedef double type;}; template<class RT, typename Env, typename Arg_> static RT eval(Env const& env, Arg_ const& arg_){ return cos(arg_.eval(env)); } }; template<typename Arg_> void cos(Arg_ const& arg_){ return compose<cos_eval>(arg_); } }} In Phoenix3, if I followed things correctly (from here https://svn.boost.org/svn/boost/sandbox/SOC/2010/phoenix3/libs/phoenix/doc/…) the new framework ask for the following, which doesn't work. The error (see at end) is difficult to decipher. What am I missing to implement this simple expression extension? -- Thanks. #include<boost/phoenix/phoenix.hpp> //v3 BOOST_PHOENIX_DEFINE_EXPRESSION( (boost)(phoenix)(cos_) , (meta_grammar) // Arg ) namespace boost { namespace phoenix { struct cos_eval{ typedef double result_type; template <typename Context, typename Arg> result_type operator()(Context const& ctx, Arg const& arg) const{ return std::cos(eval(arg, ctx)); } }; template <typename Dummy> struct default_actions::when<rule::cos_, Dummy> : call<cos_eval, Dummy> {}; template <typename Arg> typename expression::cos_<Arg>::type const cos_(Arg const& arg){ return expression::cos_<Arg>::make(arg); } }} usr/include/boost/proto/matches.hpp:846:13: error: no type named ‘proto_tag’ in ‘const struct boost::phoenix::vector2<boost::phoenix::vector2<const boost::phoenix::actor<boost::proto::exprns_::basic_expr<boost::phoenix::tag::cos_, boost::proto::argsns_::list1<boost::phoenix::actor<boost::proto::exprns_::expr<boost::proto::tag::terminal, boost::proto::argsns_::term<boost::phoenix::argument<1> >, 0l> > >, 1l> >*, double&>&, const boost::phoenix::default_actions&>’ compilation terminated due to -Wfatal-errors.

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[phoenix] Basic recursive function.
by Robert Jones 14 Apr '11

14 Apr '11

I'm a newbie to Phoenix, just exploring, but I guess my intent in this code is obvious. Can anyone tell me what I'm doing wrong? Thx - Rob. #include <iostream> #include <boost/spirit/include/phoenix_core.hpp> #include <boost/spirit/home/phoenix/operator.hpp> #include <boost/spirit/home/phoenix/statement.hpp> #include <boost/function.hpp> using namespace boost::phoenix; using namespace boost::phoenix::arg_names; using namespace std; int main() { boost::function<unsigned( unsigned )> factorial; factorial = if_else( _1 == 0, 1, _1 * factorial( _1 - 1 ) ); cout << factorial( 3 ) << endl; return 0; }

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run time error for min_max_paths.cpp of Graph Library 1.46.1 on Fedora 12
by albert kao 14 Apr '11

14 Apr '11

I compiled the min_max_paths.cpp in the example directory of BGL 1.46.1 on Fedora 12. $ g++ -I ~/boost_1_46_1 min_max_paths.cpp -o min_max_paths \ -L ~/boost_1_46_1_build/boost/bin.v2/libs/graph/build/gcc-4.4.4/release/link-static/threading-multi/ -lboost_graph Please help to solve the following run time error. $ min_max_paths terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::negative_edge> >' what(): The graph may not contain an edge with negative weight. Aborted (core dumped) My configuration is as follows: $ uname -a Linux triplecore 2.6.31.5-127.fc12.i686 #1 SMP Sat Nov 7 21:41:45 EST 2009 i686 athlon i386 GNU/Linux $ g++ -v Using built-in specs. Target: i686-redhat-linux Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla--enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --enable-plugin --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre --enable-libgcj-multifile --enable-java-maintainer-mode --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib --with-ppl --with-cloog --with-tune=generic --with-arch=i686 --build=i686-redhat-linux Thread model: posix gcc version 4.4.4 20100630 (Red Hat 4.4.4-10) (GCC)

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[format] Reuse of the format object
by Maxime van Noppen 14 Apr '11

14 Apr '11

Hi, I've got a question about the reuse of the boost::format object. Given this minimal testcase: ----------------------------------------------------------- #include <iostream> #include <boost/format.hpp> int main() { boost::format fmt("%|=12| %|=12| %|=12|\n"); // 1 std::cout << boost::str(fmt % "a" % "b" % "c") << boost::str(fmt % 1 % 2 % 3); // 2 std::cout << fmt % "a" % "b" % "c" << fmt % 1 % 2 % 3; } ----------------------------------------------------------- Why is 1 working while 2 produces the runtime exception: > terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::io::too_many_args> >' > what(): boost::too_many_args: format-string referred to less arguments than were passed ? I didn't find an explanation about this in the doc & the example about the reuse of format objects here: http://www.boost.org/doc/libs/1_46_1/libs/format/example/sample_advanced.cpp Using boost 1.46.0 and g++ 4.5.2. Thanks, -- Maxime

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