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Re: [Boost-users] [bind] Need Help - Function Composition
by Max 23 Dec '08

23 Dec '08

Thank you, Watanabe. B/Rgds Max ----- Original Message ----- From: Steven Watanabe To: boost-users(a)lists.boost.org Subject: Re: [Boost-users] [bind] Need Help - Function Composition Date: 2008-12-21 10:50:22 AMDG loadcom wrote: > I'm not sure if what you mean is that in your use case: > boost::function f = make_less_by_func(boost::bind(...)); > the temporarily constructed bind obj will go out of its lifetime before > we use it via a refence to it? Yes. the temporary is destroyed as soon as the boost::function constructor runs. f is then left with a reference to an object that has been destroyed. > But if I cannot declare > > const F& func_; > > instead of > > F func_; > > then why bother using another ref lib? > You can use a reference in some cases. Using Boost.Ref forces the caller to be explicit about whether to use a reference so presumably the user knows that it is safe. > or, in other words, is there a way to save this 'unneeded' copy > construction and allow us to use > > make_less_by_func(boost::bind(...)) > ? > There is no way to avoid the copy while maintaining this interface. However, it is quite likely that the compiler can optimize away the copy when you are only using Boost.Bind with built in types. > btw, I'm not using ref lib frequently, but should boost::unwrap_ref > be boost::unwrap_reference? > No. boost::unwrap_reference is a metafunction. In Christ, Steven Watanabe ------------------------------------------------------------------- 新浪空间——与朋友开心分享网络新生活！(http://space.sina.com.cn/ )

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[STL] Is there a std::abs<>() function?
by Max 23 Dec '08

23 Dec '08

Hello, It's strange to me that there seems not to be a std::abs<>() function in STL, with it I can write code like this: double d = std::abs(-1.0); int i = std::abs(-1); Does anybody else have the same feeling? Being uncomfortable with the abcence of it, I've wrote my own version in my namespace: #include <boost/utility/value_init.hpp> // my abs function // it works not only for POD types, but also for // user types that are default constructible and // support operator<() and unary operator-() template<class T> T abs(const T & x) { static boost::value_initialized<T> zero; return (x < zero? -x : x); } Thanks for any information. Best regards Max ------------------------------------------------------------------- 新浪空间——与朋友开心分享网络新生活！(http://space.sina.com.cn/ )

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[STL] Is there a std::abs<>() function? (Max)
by Philip Ogunbona 22 Dec '08

22 Dec '08

Max, Using STL does not prevent access to abs(), fabs() and labs(). You just need to #include <cstdlib>. Is that what you want? Philip

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Access to BGL errata?
by Roger House 22 Dec '08

22 Dec '08

When I click on BGL Book Errata at the link below, I'm asked for a username and password. The name and password I use as a Boost User Subscriber don't seem to work. What is the magic incantation needed to access the errata? Roger House Software Developer http://www.boost.org/doc/libs/1_37_0/libs/graph/doc/table_of_contents.html

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[MPI] Efficient way to have views on arrays
by Matthieu Brucher 22 Dec '08

22 Dec '08

Hi, I've started to use the MPI Boost library in conjunction with the usual C library. I'lm trying to get as much as possible done with Boost directly. I'd like to use it in a parallel finite difference loop. This means that before each iteration I have to send a strip of my computed data to each neighbor (getting the neighbors is done through a C MPI function). This can be done with MPI_Type_vector (constant-stride data) in C. Does someone know how it can be done with Boost.MPI ? Matthieu -- Information System Engineer, Ph.D. Website: http://matthieu-brucher.developpez.com/ Blogs: http://matt.eifelle.com and http://blog.developpez.com/?blog=92 LinkedIn: http://www.linkedin.com/in/matthieubrucher

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[format] format in boost 1_37_0 cause VS 2003SP1 ICE?
by Max 22 Dec '08

22 Dec '08

Hello, I have a project that makes use of some boost components, including regex, format, function, and so on. The things are well with boost of version 1.36. But after I installed boost 1.37.0 and switched the searching paths of the IDE to the ones that relate to the new boost version, I have several ICE's - internal compiler error. The IDE told me the error occured at line 203 of format\feed_args.hpp: oss2 << ' '; I've attemped to prepare a small test program that uses boost::format only to see if boost::format(1.37.0) doesn't support VS2003SP1. But it got compiled well. Anybody has similar experience or any hints of where I should go? Thanks in advance. B/Rgds Max ------------------------------------------------------------------- 新浪空间——与朋友开心分享网络新生活！(http://space.sina.com.cn/ )

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boost::serialization does not compile when archiving to xml
by Daniel Roberts 22 Dec '08

22 Dec '08

Building a Win32 console app, the following code compiles just fine: #include "stdafx.h" #include <boost/archive/text_oarchive.hpp> #include <fstream> class SomeClass { public: SomeClass() : m_foo(666), m_bar(777.f) {} private: friend class boost::serialization::access; template<class Archive> void serialize(Archive& archive, const unsigned int version) { archive & m_foo; archive & m_bar; } int m_foo; float m_bar; }; int _tmain(int argc, _TCHAR* argv[]) { SomeClass someClass; std::ofstream fileStream("TestFile.object"); boost::archive::text_oarchive oa(fileStream); oa << someClass; return 0; } but if I include xml_oarchive.hpp and create an xml_oarchive object, just changing the include statement and the type of oa, I get the following error: >c:\program files (x86)\boost\boost_1_36_0\boost\archive\basic_xml_oarchive.hpp(88) : error C2664: 'boost::mpl::assertion_failed' : cannot convert parameter 1 from 'boost::mpl::failed ************boost::serialization::is_wrapper<T>::* ***********' to 'boost::mpl::assert<false>::type' 1> with 1> [ 1> T=SomeClass 1> ] 1> No constructor could take the source type, or constructor overload resolution was ambiguous 1> c:\program files (x86)\boost\boost_1_36_0\boost\archive\detail\interface_oarchive.hpp(64) : see reference to function template instantiation 'void boost::archive::basic_xml_oarchive<Archive>::save_override<T>(T &,int)' being compiled 1> with 1> [ 1> Archive=boost::archive::xml_oarchive, 1> T=SomeClass 1> ] 1> c:\users\daniel\documents\visual studio 2008\projects\testdata\testdata.cpp(31) : see reference to function template instantiation 'Archive &boost::archive::detail::interface_oarchive<Archive>::operator <<<SomeClass>(T &)' being compiled 1> with 1> [ 1> Archive=boost::archive::xml_oarchive, 1> T=SomeClass 1> ] Basically, I can't archive into XML. Can someone please explain what I am doing wrong? I am using Windows Vista, Visual Studio 2008 and boost v36, Thanks

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Re: [Boost-users] [MultiArray] Bounds Guarding in array_view for (stride>1)
by Max 22 Dec '08

22 Dec '08

Perhaps I've not described the question quite clear. :-( What I mean is in the cases the specified stride > 1, will it cause undefined bahavior if I define the range of one dimention as range_t(first, last+stride-1, stride) (I know the correct form is range_t(first, last+stride, stride)) Thanks for any explanation. Max ----- Original Message ----- From: loadcom To: boost-users Subject: [Boost-users] [MultiArray] Bound Guarding Date: 2008-12-21 09:29:55 Hello, I'm using boost::multi_array for a while and find it very powerful except one point that I cannot specify an array_view's number of dimentions at runtime. But this pity is not the topic of this post. You know one can create an array_view with arbirary given start/bound indices as well as the stride as follows: typedef boost::multi_array array_t; array_t myarray; //... typedef array_t::index_range range_t; typename array_t::array_view::view myview = myarrray[boost::indices[range_t(0, 8, 2)][rang_t()][1]]; As I don't know in the internal of the lib how the dound guarding of iteration is done, either - in the 'standard' STL manner as i!=bound; or - in the 'conventional' C stale as ihttp://space.sina.com.cn/ ) ------------------------------------------------------------------- 新浪空间——与朋友开心分享网络新生活！(http://space.sina.com.cn/ )

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date_time question
by Amadeus W.M. 21 Dec '08

21 Dec '08

I want to read from stdin files that contain dates and data. The files come from various sources so the dates are in different formats. Of course, the problem is reading the dates. Based on the date_time examples I put together a few lines of code using facets that I thought should work, but it doesn't seem to. Can't tell if I'm way off, or I'm missing something small. #include <boost/date_time/posix_time/posix_time.hpp> using namespace boost::posix_time; using namespace std; int main(int argc, char * argv[]) { // Create a facet with the expected format. time_input_facet * tfacet=new time_input_facet("%Y/%m/%d %H:%M:%S"); ptime pt(not_a_date_time); cin.imbue(locale(cin.getloc(),tfacet)); cin >> pt; cout << pt << endl; // pt still not_a_date_time. return 0; } Compilation: g++ -g -Wall -o facets -I/usr/local/include/boost-1_35 -L/usr/local/lib/ facets.C -lboost_date_time-gcc43-mt-1_35 Run: echo "12/20/2008 09:56:00" | ./facets not-a-date-time # pt unchanged Once I sort out how to read dates from stdin (initially with the format hard-coded) I have to figure out how to parse the date and guess the format internally in the program. Please help! Thanks!

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[bind] code sample crashing MS compiler
by Christian Henning 21 Dec '08

21 Dec '08

This following code sample will crash the MS compiler version 8. I hope there are some MS folks reading this mailing list, since I have no idea where else to post this. #include <boost/bind.hpp> struct A { void operator() () { boost::bind( &A::lookup, *this, unsigned char() )(); } void lookup( unsigned char& c ) {} }; int main(int argc, char* argv[]) { A()(); return 0; } I know the code is not suppose to compile. Uncommenting the this pointer in the bind construct will make the code compile fine. Regards, Christian

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