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

[serialization] Warning "type qualifier is meaningless on cast type" in extended_type_info_typeid.hpp
by Patrik Jonsson 02 Dec '11

02 Dec '11

Hi, When I compile code that uses the 1.48.0 serialization library with icpc 12.3.174, I get this warning, along with screenfuls of instantiation context: /n/home00/pjonsson/include/boost/serialization/extended_type_info_typeid.hpp(134): warning #191: type qualifier is meaningless on cast type static_cast<T const * const>(p) ^ This is the offending code: virtual void destroy(void const * const p) const { boost::serialization::access::destroy( static_cast<T const * const>(p) ); The compiler is complaining (correctly, I think) that you can't dictate whether something returned by value (here, the T const *) is const or not. Changing the cast to: static_cast<T const *>(p) makes the warning go away. Perhaps someone can make this change? Regards, /Patrik J.

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C0x11 threading capabilities
by Erotavlas_turbo＠libero.it 02 Dec '11

02 Dec '11

Hi, I have some question about the threading programming capabilities of boost library. First question: The new C++ standard C++11 has a support for threading programming. I have read some times ago, that with high probability the threading library of the C++11 should be the same of boost library? If it is true, can I use the boost thread library and in the future, when the C++ standard will be completed, could I transparently switching to it? What are the differencies between the boost thread library and the future C++11 thread library? Second question: this question is strictly related to the first one. At the moment GCC supports only a small subset of threading programming features http: //wiki.apache.org/stdcxx/C++0xCompilerSupport. So using thread boost library allows me to use the full features of future C++ standard library? Or I'm limited by the compiler? Last question: what about the OpenMP directives? How they are different in terms power and flexibility for the parallel programming task respect to the boost library? Thank you Best Regards

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Changelog for 1.47.0 does not properly warn about critical bug
by Paul Harris 02 Dec '11

02 Dec '11

Hello, I discovered this bug by accident https://svn.boost.org/trac/boost/changeset/68866 which was only linked via the ticket mentioned below, The code below demonstrates that ANY wide-character string of the same length resolves to the same UUID ! Thats pretty darn serious, I expected to see a much more serious mention in the Changelog in boost 1.47.0... for UUID, there was only a mention of a few tickets including this one: https://svn.boost.org/trac/boost/ticket/5145 which only mentioned a WARNING in the description ! "Fixed warning: use of logical && with constant operand; switch to bitwise & or remove constant [-Wconstant-logical-operand]" Surely it should say something like "UUIDs for wide character strings are totally wrong" Note also that the Changelog link for UUID goes to Utility, not UUID. The code: #include <boost/uuid/name_generator.hpp> #include <boost/uuid/nil_generator.hpp> #include <boost/uuid/uuid_io.hpp> #include <iostream> using namespace boost::uuids; using namespace std; int main() { { cout << "WIDE" << endl; const wchar_t* a = L"one long string that is something like this and that blahh"; const wchar_t* b = L"hello there you long long string that looks nothing like t"; nil_generator nil; name_generator na(nil()); name_generator nb(nil()); uuid ua = na(a); uuid ub = nb(b); cout << to_string(ua) << endl; cout << to_string(ub) << endl; } { cout << "NARROW" << endl; const char* a = "one long string that is something like this and that blahh"; const char* b = "hello there you long long string that looks nothing like t"; nil_generator nil; name_generator na(nil()); name_generator nb(nil()); uuid ua = na(a); uuid ub = nb(b); cout << to_string(ua) << endl; cout << to_string(ub) << endl; } return 0; } the result: $ g++ main.cpp && ./a.out WIDE 4ffa48af-9685-5089-97ac-fe6627ead94c 4ffa48af-9685-5089-97ac-fe6627ead94c NARROW 73030b72-a864-5c7b-9963-c0bedff1283e da8943a6-26c9-5641-bd37-427b1b70d619 $ The two different wchar_t strings resolve to the same uuid !!! What am I doing wrong? thanks Paul

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Problem with user defined Boost Units system
by Stephen Torri 01 Dec '11

01 Dec '11

I am using Boost 1.45 and trying to use Boost Units to map the types of astrodynamic equation variables. I am getting an error with the following equation. The error is saying that the lvalue type for k2_divded_by_semi_major is wrong. The questions I have are: Q1: Did I defined my system correctly? (System file is attached - types.hpp) Q2: How do I define ratio in the system? For example I have some constants that define a conversion (1 earth radii = 6378 km). Q3: How do I define a variable type if its a fraction (e.g. radii / radian )? ---- EQUATION ---- sgp4::types::radii_t k2_divided_by_semi_major = m_k2 / pow<2> ( semi_major ); The types of variables are: m_k2 sgp4::types::radii_t semi_major sgp4::types::radian_t ---- ERROR ---- 1> [ 1> Unit=boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension,boost::units::static_rational<-1>>,boost::units::detail::merge_dimensions_impl<0,0>::apply<boost::units::dimensionless_type,boost::units::dimensionless_type>::type>,boost::units::homogeneous_system<boost::units::list<sgp4::types::radii_base_unit,boost::units::list<sgp4::types::radian_base_unit,boost::units::dimensionless_type>>>>, 1> Y=double 1> ] 1> and 1> [ 1> Unit=sgp4::types::sgp4_length_t, 1> Y=double 1> ] 1> Constructor for class 'boost::units::quantity<Unit,Y>' is declared 'explicit' 1> with 1> [ 1> Unit=sgp4::types::sgp4_length_t, 1> Y=double 1> ] Regards, Stephen

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Multicast using Asio
by Vince Deters 01 Dec '11

01 Dec '11

Hi, I'm working on a rudimentary pub/sub mechanism using Asio, with the requirement that the publisher be notified when a new subscriber appears. Using multicast, this would correspond to a subscriber joining the multicast group. But it appears there's no way for the publisher to know this, correct? If so, is the only alternative to dedicate a socket to each pub/sub pair? Thanks, Vince

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[Units] Temperature conversion problem
by Belcourt, Kenneth 01 Dec '11

01 Dec '11

Hi, There appears to be a temperature conversion problem between ºC and ºF. Here's a simple test that shows the error under both gcc and Intel on both Darwin and Linux (with Boost trunk). brisc:~ kbelco$ cat test3.cpp #include <iostream> #include <boost/units/io.hpp> #include <boost/units/quantity.hpp> #include <boost/units/systems/temperature/celsius.hpp> #include <boost/units/systems/temperature/fahrenheit.hpp> int main(int, char **) { using namespace boost::units; quantity<fahrenheit::temperature> t(100 * celsius::temperature()); // expect output of 212 F, produces 180 F // seems like not adding 32º offset when computing F = (C * 9/5 + 32) std::cout << t << std::endl; return 0; } brisc:~ kbelco$ icpc -g -Iboost test3.cpp brisc:~ kbelco$ ./a.out 180 F -- Noel

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Re: [Boost-users] [Units] Temperature conversion problem
by Alex Perry 01 Dec '11

01 Dec '11

On Wed, 30 Nov 2011 15:00:28 -0800 Matthias Schabel <boost(a)schabel-family.org> wrote: ...snip... > This will have the added benefit of allowing conversions but disallowing > operations that don't make sense... Some code: > > #include <iostream> > > #include <boost/units/absolute.hpp> > #include <boost/units/systems/temperature/celsius.hpp> > #include <boost/units/systems/temperature/fahrenheit.hpp> > #include <boost/units/systems/si/temperature.hpp> > > #include <boost/units/base_units/temperature/conversions.hpp> > > using namespace boost::units; > > int main() > { > quantity<celsius::temperature> > dTC(10.*celsius::temperature()); > quantity<fahrenheit::temperature> > dTF(10.*fahrenheit::temperature()); > quantity<si::temperature> dTK(10.*si::kelvin); > > std::cout << dTC << std::endl; > std::cout << dTF << std::endl; > std::cout << dTK << std::endl; > > quantity<absolute<celsius::temperature> > > TC(0*absolute<celsius::temperature>()); > quantity<absolute<fahrenheit::temperature> > > TF(32.*absolute<fahrenheit::temperature>()); > quantity<absolute<si::temperature> > > TK(0.*absolute<si::temperature>()); > > std::cout << TC << std::endl; > std::cout << TF << std::endl; > std::cout << TK << std::endl; > > std::cout << quantity<absolute<celsius::temperature> >(TF) << > std::endl; > std::cout << quantity<absolute<celsius::temperature> >(TK) << > std::endl; > > std::cout << quantity<absolute<fahrenheit::temperature> >(TC) << > std::endl; > std::cout << quantity<absolute<fahrenheit::temperature> >(TK) << > std::endl; > > // std::cout << TC+quantity<absolute<celsius::temperature> >(TF) << > std::endl; // fails because you cannot add two absolute temperatures > std::cout << TC+quantity<celsius::temperature>(dTF) << std::endl; > std::cout << TF+quantity<fahrenheit::temperature>(dTC) << > std::endl; > > return 0; > } Not being a current user of boost units I was curious about above code and just thought I'd try it (it looked totally straightforward and I was thinking hmm maybe I should be using boost units at times) - However it didn't compile (msvc 2010 and boost 1.48) - It wasn't exactly hard to change it so it would compile - just played around a little and ended up adding :- #include <boost/units/quantity.hpp> #include <boost/units/io.hpp> However given your email had outputs pasted in so obviously code was running at some point I wondered : Was this just a cut & paste typo? Or do you need to be careful with headers in code using boost unit to make sure that it compiles x-platform or some such? Alex

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[phoenix] problem when trying to access member via arg1
by Christian Hoffmann 01 Dec '11

01 Dec '11

Hi, I have below test program in which I try to call a function on each map object. It compiles and runs fine with gcc 4.5 but not on vc10. Is arg1 and ->* operator supposed to work when arg1 is an object and not pointer? Or is there another way of accessing members with arg1 (i.e. without phoenix::bind)? Regards, Chris ----------------------- #include <boost/phoenix/core.hpp> #include <boost/phoenix/operator.hpp> #include <iostream> #include <vector> #include <boost/range/algorithm.hpp> #include <boost/shared_ptr.hpp> #include <boost/shared_ptr.hpp> struct A { void f (int s) const { std::cout << "Calling f (" << s << ")...\n"; } }; int main (int argc, const char **argv) { typedef std::map<int, boost::shared_ptr<A> > map_type; typedef map_type::value_type value_type; map_type a_map; a_map[3] = boost::shared_ptr<A> (new A ()); namespace phoenix = boost::phoenix; using phoenix::arg_names::arg1; boost::for_each (a_map, ((arg1->*&value_type::second)->*&A::f) (10)); } ---------------------------

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Subversion repository not accessible as anonymous
by Marko Lindqvist 01 Dec '11

01 Dec '11

http://www.boost.org/users/download/#repository says that "Anonymous, read-only access to the Boost Subversion repository is available at http://svn.boost.org/svn/boost." My attempts to make checkout results in svn prompting for credentials. Seems like misconfiguration to me. - ML

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Using hash_range with polymorphism
by Kelvin Chung 01 Dec '11

01 Dec '11

I'm having a hard time reconciling two distinct notions. Suppose I have a class hierarchy with root class Foo, and subclasses Foo1, Foo2, etc. (all of which are leaf classes) Now, suppose that hash_value() is defined for all the subclasses but not Foo itself (say, if Foo was abstract). Now suppose I have this: struct FooList { std::vector<boost::shared_ptr<Foo>> foos; } std::size_t hash_value(const FooList& list) { std::size_t seed = 0; typedef boost::indirect_iterator<std::vector<boost::shared_ptr<Foo>>::const_iterator> Iterator; boost::hash_range(seed, Iterator(list.foos.begin()), Iterator(list.foos.end()); return seed; } This seems a bit incorrect (and it would fail to compile due to "ambiguous overload" of hash_combine or something). What I want to do is something along the lines of std::size_t hash_value(const FooList& list) { std::size_t seed = 0; for (std::vector<boost::shared_ptr<Foo>>::const_iterator it = list.foos.begin(); it != list.foos.end(); ++it) { boost::hash_combine(seed, **it); } return seed; } That is, hash the Foos pointed to by the foos (using the correct derived class hash_value() functions) and not the shared_ptrs themselves. Is there a "shorter" version of the latter (which I presume is correct), or will the latter have to do?

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