February 2005 - Boost-users - lists.preview.boost.org

New article on BOOST_FOREACH
by Eric Niebler 18 Feb '05

18 Feb '05

For anybody interested in peeking under the hood of BOOST_FOREACH, there is a new article about it at The C++ Source (http://www.artima.com/cppsource/index.jsp) It focuses mainly on the conditional operator and how to use it to write macrco's that do not reevaluate their arguments. -- Eric Niebler Boost Consulting www.boost-consulting.com

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problem with lambda and function<>
by Arturo_Cuebas＠bpmicro.com 18 Feb '05

18 Feb '05

Given: #include <map> #include <boost/mem_fn.hpp> #include <boost/function.hpp> #include <boost/lambda/lambda.hpp> #include <boost/lambda/bind.hpp> using namespace std; using namespace boost; using namespace boost::lambda; struct s { int key (){return 1;} int value(){return 2;} }; typedef map<int, int> int_map; int_map m; var_type<int_map>::type delayed_m(var(m)); template<class F> void execute(F f) { s o; f(o); } Why does this work?: int main() { execute ( delayed_m[lambda::bind(&s::key, lambda::_1)] = lambda::bind(&s::value, lambda::_1) ); } But this doesn’t?: int main() { function<int (s &)> key (mem_fn(&s::key )), value(mem_fn(&s::value)); execute ( delayed_m[key] = value //compile error instantiation backtrace leads to here ); } I’m using VC7.1. Here's the error (sorry that it's so noisy): c:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\boost\lambda\detail\operator_lambda_func_base.hpp(255) : error C2440: '=' : cannot convert from 'const boost::tuples::cons<HT,TT>::stored_head_type' to 'int' with [ HT=const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type, TT=boost::tuples::detail::map_tuple_to_cons<boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>::type ] No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called c:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\boost\lambda\detail\lambda_functors.hpp(153) : see reference to function template instantiation 'RET boost::lambda::lambda_functor_base<Act,Args>::call<boost::lambda::lambda_functor_base<Act,Args>::sig<SigArgs>::type,A,const boost::tuples::null_type,const boost::tuples::null_type,const boost::tuples::null_type>(A &,B &,C &,Env &) const' being compiled with [ RET=boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map &>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>::sig<boost::tuples::tuple<s &,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>::type, Act=boost::lambda::other_action<boost::lambda::assignment_action>, Args=boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boos t::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map &>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>, SigArgs=boost::tuples::tuple<s &,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>, A=s, B=const boost::tuples::null_type, C=const boost::tuples::null_type, Env=const boost::tuples::null_type ] c:\TestApps\GeneralTests\GeneralTests.cpp(27) : see reference to function template instantiation 'boost::lambda::lambda_functor_base<Act,Args>::sig<SigArgs>::type boost::lambda::lambda_functor<T>::operator ()<s>(A &) const' being compiled with [ Act=boost::lambda::other_action<boost::lambda::assignment_action>, Args=boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map &>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>, SigArgs=boost::tuples::tuple<s &,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>, T=boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map &>>,const boost::lambda::detail: :parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>, A=s ] c:\TestApps\GeneralTests\GeneralTests.cpp(47) : see reference to function template instantiation 'void Execute<boost::lambda::lambda_functor<T>>(F)' being compiled with [ T=boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map &>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>, F=boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::assignment_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::other_action<boost::lambda::subscript_action>,boost::tuples::tuple<boost::lambda::lambda_functor<boost::lambda::identity<int_map &>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost ::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>>,const boost::lambda::detail::parameter_traits_<const boost::function<int (s &)>,const boost::lambda::detail::IF<false,const boost::function<int (s &)> &,const boost::function<int (s &)>>::RET>::type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>> ]

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I'm looking for applications using Boost and STL with source code available
by Matthew Johnson 18 Feb '05

18 Feb '05

I would like to study a gui application designed from the ground up with modern C++ techniques and built on top of STL and Boost. Ideally I am looking for an application that abstracts the system specific ui components (windows, controls, etc) as much as possible. The ideal application would: Implement significant, non-trivial functionality. Be elegant and efficient. Use modern C++ and implementation design techniques. Be built on top of STL and Boost. Use the best techniques for the job (metaprogramming, generic programming, functional programming, oo, etc) Have source code available for study (not necessarily available for legal use). Last but not least, a native Mac OS X application would be ideal. Does anyone here know of any applications that meet these requirements? I have been studying modern C++ for a while now and would like to study real world applications and uses of the these techniques and libraries as a next step in this study. Thanks, Matthew

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unit test and BOOST_CHECK_CLOSE
by Thomas Lemaire 17 Feb '05

17 Feb '05

dear list, When executing a test defined by: BOOST_CHECK_CLOSE(t3.x(3), 0.0, epsilon); I get the message: difference between t3.x(3){2.34188e-17} and 0.0{0} exceeds 1e-08% where obviously the difference does not exceeds the given threshold 1e-08... What's going on ? -- thomas

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metaprogramming exercise 2-0
by Chris Goller 17 Feb '05

17 Feb '05

I just finished the first exercise in the C++ meta programming book. Then I checked what had been done before on this mailing list. Here is my solution: using namespace boost; template <bool use_ref, typename T> struct add_const_ref_impl { typedef T const & type; }; template <typename T> struct add_const_ref_impl<true, T> { typedef T type; }; template<class T> struct add_const_ref { typedef typename add_const_ref_impl<is_reference<T>::value, T>::type type; }; From Bruce Trask comes: using namespace boost; template<typename T> struct add_const_ref { typedef typename add_reference<typename add_const<T>::type>::type type; }; His solution is SO much better then mine. However, when I first saw it I thought it must be wrong because I assumed that add_const on a reference would would return a const reference. In other words, the code below would be false: bool a = is_same<add_const<int &>::type, int &>::value; However! bool "a" is true. So my question is why is "a" true? Why isn't add_const<int &>::type == int const &? Thanks, Chris

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Re: [Boost-users] unit test and BOOST_CHECK_CLOSE
by Vladimir Krasovsky 17 Feb '05

17 Feb '05

Hello Thomas, Thursday, February 17, 2005, 1:35:48 PM, you wrote: Thomas> dear list, Thomas> When executing a test defined by: Thomas> BOOST_CHECK_CLOSE(t3.x(3), 0.0, epsilon); Thomas> I get the message: Thomas> difference between t3.x(3){2.34188e-17} and 0.0{0} exceeds 1e-08% Thomas> where obviously the difference does not exceeds the given threshold 1e-08... Thomas> What's going on ? As I remember, tolerance should be given in percents. See http://www.boost.org/libs/test/doc/components/test_tools/floating_point_com… for more detailed description of algorithm used in BOOST_CHECK_CLOSE. Either I do not understand something or you cannot use BOOST_CHECK_CLOSE for direct comparison with 0.0. Inequations given never satisfied in case one of arguments is zero. I think you could write BOOST_CHECK(t3.x(3) >= -epsilon && t3.x(3) <= epsilon); given that epsilon is non-negative. -- Best regards, Vladimir mailto:vkrasovsky@yandex.ru

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Interval Arithmetic Tribool
by Robert Ferguson 16 Feb '05

16 Feb '05

Dear list, I hope I am writing to the correct place, and that this isn't a frequently asked question.. but I'd like to know alittle about comparisons and the Interval library. I am using intervals in a search algorithm to take advantage of the natural inclusion function as proposed in a paper I'm trying to implement. So far so good, except that I'm a little unhappy that I have to use "try" and "catch" to detect the indeterminate case. I'd like to use the boost::logic::tribool to identify the semi-frequent indeterminant case. For example: tribool cmp = interval1 < interval2; if (!indeterminate(cmp)) { if (cmp) { // something } else { // something else } else { // something } When I do this and the indeterminate case happens, an exception triggers and the function quits. This could be an error on my behalf, but it seems like this the default behavior. Its not that I can't do the try, catch, its just a matter of style. Can I have my cake and eat it too? Best, Robert Ferguson

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Program runs OK in Cygwin, but got "Segment Fault" in Linux
by Welson Sun 16 Feb '05

16 Feb '05

Hi, The program is really simple, it creates a graph and output to a .dot file using the graphviz library in the BGL. It runs well in Cygwin, but in Linux, it got a segment fault when outputing the vertex id. Can you C++ gurus see what is going on? Thanks! Welson

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[Important] Mailing list downtime this Saturday, February 19
by Doug Gregor 16 Feb '05

16 Feb '05

The Open Systems Lab, which hosts most of the Boost mailing lists, will be migrating to new hardware this Saturday. The outage will be this Saturday, February 19 starting at noon Eastern Standard Time and should not last more than 8 hours. lists.boost.org will be unavailable during the outage as will the mailing lists themselves. Thanks, Doug Gregor

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[Boost.Test] and assert()
by Richard Jennings 16 Feb '05

16 Feb '05

When testing my program using the Unit Test Framework I find that if the program fails an assert() it is aborted with the message "Abnormal program termination" and no more tests are run. Is this the expected behaviour? The release notes for Boost.Test v1.30.0 say that a handler was added for SIGABRT (raised by abort() called by assert()) so I was expecting the test framework to catch this exception and report it in a similar way to a divide-by-zero error. I have my code compiled in debug with Borland C++ Builder 6.0 running on Windows XP. The behaviour is the same whether the command line option --catch_system_errors=yes or no. Richard

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