- Boost-users - lists.boost.org

Struggling to compile encfs, linking with boost library
by Jean Jordaan 22 Mar '09

22 Mar '09

Hi there I want to use encfs on a box with a Debian distro that doesn't have recent encfs and boost packages available, so I'm compiling them from source. I installed boost like this:: $ ./configure --prefix=/home/zope/local It seems to complete fine. This incantation finds the libraries, but dies shortly thereafter:: zope@iwlearn:/home/zope/src/encfs-1.5$ CPPFLAGS=-I/home/zope/local/include/boost-1_38 ./configure --with-boost-libdir=/home/zope/local/lib --prefix=/home/zope/local [...] checking for boostlib >= 1.34... yes checking whether the Boost::System library is available... yes checking for exit in -lboost_system-gcc41-mt-1_38... yes configure: WARNING: BOOST_CPPFLAGS -I/usr/include checking whether the Boost::Serialization library is available... yes checking for exit in -lboost_serialization-gcc41-mt-1_38... yes checking whether the Boost::Filesystem library is available... yes checking for exit in -lboost_filesystem-gcc41-mt-1_38... no checking for exit in -lboost_filesystem-gcc41-mt-1_38... (cached) no checking for exit in -lboost_filesystem-gcc41-mt-1_38... (cached) no checking for exit in -lboost_filesystem-gcc41-mt... no checking for exit in -lboost_filesystem-gcc41-mt... (cached) no configure: error: Could not link against boost_filesystem-gcc41-mt ! I wonder why "checking for exit" works in -lboost_serialization-gcc41-mt-1_38 and not in -lboost_filesystem-gcc41-mt-1_38 .. What does that mean, "checking for exit"? (Googling ..) -- jean . .. .... //\\\oo///\\

2 4

Boost and C++ "physical design"
by Yang Zhang 22 Mar '09

22 Mar '09

I have a couple questions about Boost and its implications for the "physical design" of C++ projects. I'm guessing there probably aren't that many non-member, non-template functions in the Boost library, but of the ones that exist, are these usually labeled `static`, since boost is mostly a header library? Is there any advice on taming (1) the generated code size and/or (2) the build times* which result from using a header-mostly library like Boost? A large C++ project consists of many translation units (.o files) which are generated from source files that include many of the same Boost headers over and over again. (2) can be ameliorated with a distributed build process, but the more general issue here is that of consumption of compute resources, be it time or machines. -- Yang Zhang http://www.mit.edu/~y_z/

7 7

[numeric::converter] finding the smallest c such that (a/c) + (b/c) < inf
by er 22 Mar '09

22 Mar '09

Hi All, template<typename T> struct promote{}; template<> struct promote<float> : mpl::identity<double>{}; template<> struct promote<double> : mpl::identity<long double>{}; template<typename T> //T: float, double struct fit_a_plus_b_to_range{ static T divider(T a, T b){ static const T mx = math::tools::max_value<T>(); static const T mi = math::tools::min_value<T>(); if(a > (mx - b)){ typedef typename promote<T>::type prom_t; typedef numeric::converter<T,prom_t> up_t; typedef numeric::converter<prom_t,T> down_t; prom_t au = up_t::convert(a); prom_t bu = up_t::convert(b); prom_t mu = up_t::convert(mx); prom_t cu = ((au/mu)+(bu/mu)); T delta = ...; T c = down_t::convert(cu) + delta; BOOST_ASSERT(!math::isinf((a/c)+(b/c))); return c; }else{ return (T)(1); } } }; With delta = 0.0 the assertion fails, with delta = 1.0 it works (for a few examples). What's the smallest delta value? Is there a better way to do this overall? If this is off topic, let me know...

2 3

Serialization of a std::vector< boost::shared_ptr< A > > throws unregistered_class exception
by Benoit Gagnon 21 Mar '09

21 Mar '09

Given the following classes: class Building { ... }; class House : public Building { ... }; class Hospital : public Building { ... }; With appropriate serialization method templates such as: class House: public Building { friend class boost::serialization::access; template<class Archive> void serialize(Archive& ar, const unsigned int version ) { ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP( Building ); ar & BOOST_SERIALIZATION_NVP( mNumBedrooms ); ar & BOOST_SERIALIZATION_NVP( mNumBathrooms ); } ... I have the following registrations in main.cpp where the archiving/ restoring is performed: BOOST_SERIALIZATION_SHARED_PTR( Building ) BOOST_SERIALIZATION_SHARED_PTR( House ) BOOST_SERIALIZATION_SHARED_PTR( Hospital ) In main.ccp, I would like to serialize a std::vector< boost::shared_ptr< Building > > object. Like this: std::vector< boost::shared_ptr< Building > > buildings; ... std::ofstream ofs( "archive.txt" ); boost::archive::text_oarchive oa( ofs ); oa & BOOST_SERIALIZATION_NVP( buildings ); This compiles correctly but fails at runtime with a "unregistered_class" exception. The individual classes (Building, House, Hospital) can be serialized and restored fine individually. That is true for objects, pointers and shared_ptr. A vector of plain pointers to any of those types also works fine. But a vector of shared_ptr to any of those types fails at runtime.. What kind of registration must be done to achieve this?

3 7

[math] log_max_value<long double>
by er 21 Mar '09

21 Mar '09

Hi All, Was this discussed before? <cmath> using namespace math::tools; typedef double RealType; log_max_value<RealType>() 709 log(max_value<RealType>()) 709.783 !math::isinf(exp(log_max_value<RealType>())) //true typedef long double RealType; log_max_value<RealType>() 11356 log(max_value<RealType>()) inf !math::isinf(exp(log_max_value<RealType>())) //false i.e. exp in cmath seems to "assume" RealType = double. i686-apple-darwin9-gcc-4.0.1

2 2

shared_ptr as reference argument
by anony 20 Mar '09

20 Mar '09

Is there some utility in passing shared_ptr's as references as here: void bla(boost::shared_ptr<T>& bla_ptr); This avoids creating of a new object and copying overhead, but is it safe? When would you recommend it and when not?

6 18

[Tuple] Help getting started with Tuple-based meta-programming
by Dominique Devienne 20 Mar '09

20 Mar '09

Hi All. I outline below code I keep writing which I'd like to replace with a sql_get_rows template function which would use the meta-type information bundled in the tuple declaration to automatically make as many calls to the get<T> function based on the tuple length, and "pack" the result of these calls into a tuple instance added to a container (vector in this case, but if it could be generalized to any container, all the better, although I'd be happy just with vector). I have experience with basic template stuff, and a little less basic stuff like CRTP, enable_if, and the like, but meta-programming is still new to me, which is why I'm seeking advice from experts to find out whether the below is : 1) possible, 2) would perform ok, and 3) where I should start looking to see examples doing this particular "tuple-enrolling" or perhaps even pseudo code outlining how one would go about implementing this, provided answers to (1) and (2) are positive of course. I suspect mpl and phoenix would need to be used, from the reading I've done, but the path to follow is quite unclear to me still. Any help in this matter would be appreciated. Thanks, --DD // Context: retrieving all the rows (result set) from a given SQL query. // pseudo code of boilerplate code I keep repeating right now struct { int id; std::string name; } Row; void doit() { ResultSet rset = sql_exec("select id, name from t"); std::vector<Row> rows; while (rset.hasMoreRows()) { Row row; row.id = rset.get<int>(0); row.name = rset.get<const char*>(1); rows.push_back(row); } // process rows } // Code I'd like to write instead void doit() { typedef boost::tuple<int, std::string> Row; std::vector<Row> rows; sql_get_rows("select id, name from t", rows); // optional arg to get only first N elements // process rows } PS: returning the vector would be better, but because of the copy involved I guess I must pass it as a non-const ref instead, to fill it up. Will the new move semantic from the upcoming standard allow a function to return the vector without the copy? Just curious.

2 2

[lambda] problem with g++
by Michał Nowotka 20 Mar '09

20 Mar '09

following code does not compile with g++ while under vs2008 it works fine: //window.h ///(...) class Window { //(...) protected: //(...) double evaluate(const vector<double>& win_probabls) const; //(...) } //(...) //window.cpp #include "window.h" #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> #include <algorithm> #include <numeric> #include <cmath> //(...) double Window::evaluate(const vector<double>& win_probabls) const { return accumulate (win_probabls.begin(), win_probabls.end(), 0.0, lambda::_1 + lambda::bind(log, lambda::_2) ); } //(...) g++ returns following error: src/window.cpp:92: error: no matching function for call to 'bind(<unresolved overloaded function type>, const boost::lambda::lambda_functor<boost::lambda::placeholder<2> >&)' make: *** [build/window.o] Error 1 and I don't know what shuld I change to make it work for me... -- Regards Michał Nowotka

2 1

[Tuple] online doc for 1.38 links to empty page
by Dominique Devienne 20 Mar '09

20 Mar '09

FYI: The link http://www.boost.org/doc/libs/1_38_0/libs/tuple/doc/tuple_advanced_interfac… referenced from http://www.boost.org/doc/libs/1_38_0/libs/tuple/doc/tuple_users_guide.html yields an empty page (modulo the page banner). The link is correct OTOH in my local install. Thanks, --DD

2 1

Re: [Boost-users] No packets received with boost::asio::ip::udp::socket set to multicast group
by danielej 20 Mar '09

20 Mar '09

I think you need to bind to the multicast group, not the interface, in linux(as I discovered this week, it is the opposite in windows.) I am still trying to figure out how to specify the interface in linux using join_group so if you find out how please add that to the post. hope this helps, Dan -- View this message in context: http://www.nabble.com/No-packets-received-with-boost%3A%3Aasio%3A%3Aip%3A%3… Sent from the Boost - Users mailing list archive at Nabble.com.

1 0