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

[serialization] infinite floating point values
by Johan Råde 05 Jul '06

05 Jul '06

I just replaced the binary archives by text archives in an app, to make sure that the archives will be portable between 32 and 64 bit platforms. But when I use text archives, the app crashes. The problem is: Text archives do not handle infinite values of type float and double. --- Example ---------------------------------------------------------- #include <iostream> #include <limits> #include <sstream> #include <boost/archive/text_iarchive.hpp> #include <boost/archive/text_oarchive.hpp> #include <boost/format.hpp> int main() { std::stringstream ss; { boost::archive::text_oarchive oa(ss); double inf1 = std::numeric_limits<double>::infinity(); std::cout << boost::format("Save: %1%\n") % inf1; oa << inf1; } { boost::archive::text_iarchive ia(ss); double inf2; ia >> inf2; std::cout << boost::format("Load: %1%\n") % inf2; } } --- Output ---------------------------------------------------------- Save: 1.#INF Load: 1 --------------------------------------------------------------------- There are two infinite values of type double, std::numeric_limits<double>::infinity() and -std::numeric_limits<double>::infinity(). These could be represented as "inf" and "-inf" in the archive. I would be very useful for me if this functionality were added to the serialization library. (Otherwise I will have to do a lot of code rewriting, or stick binary archives.) One could also consider handling nan (not a number), but that is maybe a lower priority. --Johan Råde rade(a)maths.lth.se

2 4

[spirit] working with end_p
by Neil Hunt 05 Jul '06

05 Jul '06

Hello all, Given a simple spirit grammar (simplified from my real grammer and untested) such as: file = *line; line = sensible_line >> ending >> *comment; sensible_line = confix_p( '\"', *c_escape_ch_p, '\"' ); comment = !( ch_p(';') >> ( anychar_p - eol_p ) ) >> ending; ending = *blank_p >> ( eol_p | end_p ); Note: any given line can be legitimately terminated by the end of the file or end of line And there can be arbitrary numbers of comment lines between sensible lines. However since 'comment' is terminated with 'ending', the parser ends up in an infinite loop matching the kleene star on end_p because it returns zero length (doesn't advance the scanner). At least I think this is the problem. By using: ending = *blank_p >> eol_p ; the parser runs to completion, but any given line must be terminated by an end of line sequence. Any suggestions on how to fix this problem? Thanks for any help offered, Neil Hunt

2 1

error using lambdas: conversion from 'x' to non-scalar type 'y'
by klaus triendl 05 Jul '06

05 Jul '06

Hi, I'm rather new to lambdas. I wanted to use them to stream objects into a special stream (not a stl stream). the following code outlines the situation: ---- #include <iostream> #include <list> #include <algorithm> #include <boost/ref.hpp> #include <boost/shared_ptr.hpp> #include <boost/lambda/lambda.hpp> using namespace std; using namespace boost; using boost::lambda::_1; class MyStream { public: MyStream() {} }; class MySubStream: public MyStream { public: MySubStream(MyStream*) {} }; MyStream& operator <<(MyStream& os, const int&) { return os; } int main() { list<shared_ptr<int> > cont; MyStream osTop; MySubStream osSub(&osTop); for_each(cont.begin(), cont.end(), ref(osSub) << *_1); return 0; } ---- g++ outputs error: '/usr/include/boost/lambda/detail/operator_lambda_func_base.hpp:212: error: conversion from 'MyStream' to non-scalar type 'MySubStream' requested'. MS VC 2003.net says: boost\lambda\detail\operator_lambda_func_base.hpp(212) : error C2664: 'MySubStream::MySubStream(MyStream *)' : cannot convert parameter 1 from 'MyStream' to 'MyStream *'. The question is whether my code is correct at all and how I could use lambdas the right way. Thanks! Klaus Triendl

2 4

Re: [Boost-users] shared_ptr + const_cast woes
by Evan Drumwright 04 Jul '06

04 Jul '06

Hi guys, Thanks for your help, in particular Stefan's reworked code fragment. I actually did read the documentation for shared_ptr (in particular, the section on const_pointer_cast), but got confused by the counterexample (I thought that it was saying not to use a temporary). Thanks again, Evan >Message: 5 >Date: Wed, 28 Jun 2006 10:33:19 -0400 >From: me22 <me22.ca(a)gmail.com> >Subject: Re: [Boost-users] shared ptr + const_cast woes >To: boost-users(a)lists.boost.org >Message-ID: <fa28b9250606280733u5125fa01p92da87e1e8f9ad0f(a)mail.gmail.com> >Content-Type: text/plain; charset=UTF-8; format=flowed >Take a closer look at what this is doing: >> boost::shared_ptr<const int> y(const_cast<const >int*>(x.front().get())); >To be more explicit, it's the same as > int *ip = x.front().get(); > int const *cip = ip; > boost::shared_ptr<const int> y( cip ); >At y you're creasing another shared_ptr to the same address that >doesn't share ownership with the one in x.front(). > >What you really want is const_pointer_cast : >http://boost.org/libs/smart_ptr/shared_ptr.htm#const_pointer_cast > >From the documentation for the above-mentioned const_pointer_cast: >Notes: the seemingly equivalent expression >shared_ptr<T>(const_cast<T*>(r.get())) >will eventually result in undefined behavior, attempting to delete the same >object twice. >Which is exactly your problem. > >~ Scott McMurray ------------------------------ >Message: 6 >Date: Wed, 28 Jun 2006 11:59:12 -0230 >From: Stefan Tarrant <stefan.tarrant(a)c-core.ca> >Subject: Re: [Boost-users] shared ptr + const_cast woes >To: boost-users(a)lists.boost.org >Message-ID: <44A29238.9040800(a)c-core.ca> >Content-Type: text/plain; charset=ISO-8859-1; format=flowed >When you use get() all bets are off. You are basically taking >responsibility for the ownership of the returned pointer yourself, which is >generally a bad idea. Use a const_pointer_cast<T> instead. >Here is my re-worked example: > >#include <vector> >#include <iostream> >#include <boost/shared_ptr.hpp> > >int main() >{ > std::vector<boost::shared_ptr<int> > x; > x.push_back(boost::shared_ptr<int>(new int)); > *x.front() = 4; > std::cout << "use count: " << x.front().use_count() << std::endl; > boost::shared_ptr<const int> y = x.front(); > std::cout << "use count: " << x.front().use_count() << std::endl; > std::cout << "use count: " << y.use_count() << std::endl; > boost::shared_ptr<int> z = boost::const_pointer_cast<int>(y); > std::cout << "use count: " << z.use_count() << std::endl; > std::cout << "use count: " << y.use_count() << std::endl; > x.pop_back(); > std::cout << *y << std::endl; > std::cout << "use count: " << z.use_count() << std::endl; > std::cout << "use count: " << y.use_count() << std::endl; > > y.reset(); > std::cout << "use count: " << z.use_count() << std::endl; > std::cout << "use count: " << y.use_count() << std::endl; >} > >And the output: > >use count: 1 >use count: 2 >use count: 2 >use count: 3 >use count: 3 >4 >use count: 2 >use count: 2 >use count: 1 >use count: 0 >Press any key to continue . . . > >-- >Stefan Tarrant >Senior Project Engineer >C-CORE >Captain Robert A. Bartlett Building >Morrissey Road >St. John's, NL >Canada A1B 3X5

1 0

boost pool
by michelle Tchicaya 04 Jul '06

04 Jul '06

Hello, I am very new to C++. And I want to use Boost thread and Boost Pool to create a multithreaded application which will handle real time messages. I need ONE Boost Pool. But I dont know how to combine it with thread Thank a lot for your help mimi

1 0

Re: [Boost-users] [boost] Convert function pointer type to function type
by Peter Soetens 04 Jul '06

04 Jul '06

Quoting Peter Dimov: > Peter Soetens wrote: >> Hi, >> >> I'm desperately seeking for doing this conversion using the boost >> libraries. User code often provides a function pointer, while library >> code often works with function types. [...] > > One obvious way is > > template<class F> boost::function<F> function_wrapper( F * pf ) > { > return boost::function<F>( pf ); > } > > but a more interesting question is why do you need a function_wrapper at > all. Everything that you could do with the returned function<F> (call it) is > also possible with pf itself. Looking at the simplicity of that answer, this was clearly a boost-users question :-]. Sorry. This was a minimalistic example, removing the context. The big picture uses boost::function<F> to store partially bound objects, since this is a way to store the result of boost::bind for later use in a not templated class. I got confused by the boost::function_traits<T>, which only takes a "function type" and not a "function pointer type." I assumed one was not convertible to the other. I tried using boost::remove_pointer<F>, which didn't work and confirmed back then my assumption (confusingly, is_pointer<F> did work, but I could not remove it using type_traits...) My books write about function pointer types but do not mention 'function types'. These concepts appear to me underdocumented in standard C++ works. *Thanks a lot*. Peter -- www.fmtc.be ---------------------------------------------------------------- This message was sent using IMP, the Internet Messaging Program.

1 0

Re: [Boost-users] [BGL] All Possible Matchings (Hossein Haeri)
by Grégoire Dooms 04 Jul '06

04 Jul '06

boost-users-request(a)lists.boost.org wrote: Message: 9 Date: Mon, 3 Jul 2006 16:46:55 +0100 (BST) From: Hossein Haeri <powerprogman(a)yahoo.com> Subject: [Boost-users] [BGL] All Possible Matchings To: boost-users(a)lists.boost.org Message-ID: <20060703154655.35182.qmail(a)web53405.mail.yahoo.com> Content-Type: text/plain; charset=iso-8859-1 > Dear all, > > I have a bipartite graph, and want to generate all its > possible matchings. Any suggestions? > You should have a look at Constraint Programming and the Alldifferent constraint. In CP, the task of filtering for a constraint over some integer variables amounts to partitioning, for each of its variables, the potential values into three categories: the values participating in all solutions (obviously at most one per variable), the values participating in some solutions, and the values participating in no solutions. In the case of the Alldifferent constraint, it can be reinterpreted in graph matching terms: Build a bipartite variable-value graph. A solution to the Alldifferent constraint is a maximum matching covering all variables in this graph. Hence filtering can be done by identifying edges which belong to some/all/no max matching. In a nutshell, the following property of matchings is used [Peterson] [Berge] : M1 (+) M2 = P M1 (+) P = M2 where P is an alternating path (for instance, look at the LEDA book for a good exposition of this property and matching algorithms). This property is used in matching algorithms with P an augmenting alternating path. If you consider "maintaining" paths (eg. non-augmenting and non-decreasing -- even length, starting at a free node and ending at a covered node, or an alternating cycle) and apply them on a max matching you get another max matching. Here are a few references: Ref. to the original paper : http://citeseer.ist.psu.edu/context/210815/0 A survey on this subject: http://citeseer.ist.psu.edu/579391.html (or http://www.cs.cornell.edu/~vanhoeve/papers/alldiff.pdf for a more recent/in progress version) Slides by JC Regin: http://www.constraint-programming.com/people/regin/papers/GraphAndCP.pdf Finally, an open-source implementation: http://www.gecode.org/gecode-doc-latest/distinct_2dom_8icc-source.html Hope this helps, -- Grégoire Dooms.

1 0

When to use thread.join()
by Simon Reye 04 Jul '06

04 Jul '06

My apologies if this has been covered. I am new to boost and have been working with the boost thread class. I assume that the join() function waits for the thread to finish execution. But what if the thread has already finished executing? Can I still call join() and have it not wait for infinity? Simon

2 2

[Spirit] puts namespace std into the global scope
by Johan Råde 04 Jul '06

04 Jul '06

It seems that the header boost/spirit.hpp puts the entire namespace std into the global scope. That is not very nice! --- Example 1 -------- #include <string> #include <sstream> #include <fstream> #include <vector> #include <boost/spirit.hpp> void f() { string s; istringstream iss; ofstream ofs; vector<int> v; } ---------------------- Example 1 should not compile (undefined symbols), but does compile. If the line #include <boost/spirit.hpp> is removed, then Example 1 does not compile. --- Example 2 -------- #include <boost/filesystem/path.hpp> #include <boost/filesystem/fstream.hpp> #include <boost/spirit.hpp> using boost::filesystem::path; using boost::filesystem::ifstream; void g() { path p; ifstream ifs(p); } ---------------------- Example 2 should compile but does not. The compiler complains that the symbol ifstream is ambigous. If the line #include <boost/spirit.hpp> is removed, then Example 2 does compile. I´m using Boost 1.33.1 and MSVC 7.1 on a Windows XP computer. --Johan Råde rade(a)maths.lth.se

3 3

auto-diff expression templates-> MPL
by Russell L. Carter 03 Jul '06

03 Jul '06

Greetings, This is a beginner question about the MPL. I'm building a general purpose simulation program which will have an optimization module as well as an internal ODE solver which requires derivatives of the implemented algorithm in various forms. Around 1998-2002 there was a lot of enthusiasm for generating the derivatives automatically using expression templates. I'm not quite through with an exhaustive review of the literature but it appears the various efforts ran to ground on the compilation memory and cpu requirements that evaluating expression templates in their original form required. So 1st question, has anybody done something like this with mpl/fusion sequences and algorithms? Has there been an improvement in compile time performance? Do you have any pointers to trivial examples? I've read Alexandrescu, and Abrahams & Gurtovoy and it's not clear to me how to map the expression templates as described in the earlier efforts onto mpl sequences and algorithms. That's probably enough for now. Thanks for any help. Russell

1 0