July 2006 - Boost-users - lists.preview.boost.org

[mpl] Placeholders substitution and template partial specialization
by Andriy Tylychko (mail.ru) 25 Jul '06

25 Jul '06

Hi All Consider following example: BOOST_MPL_ASSERT((boost::is_same< mpl::apply<mpl::apply<_1, _2>::type, boost::add_pointer<_1>, int>::type , int*>)); It should apply "add_pointer" to "int" and receive "int*", but it doesn't work. It returns just "int". Consider another example: template <class F, class X> struct apply1: mpl::lambda<F>::type::template apply<X> {}; BOOST_MPL_ASSERT((boost::is_same< mpl::apply<apply1<mpl::_1, mpl::_2>/*nothing here*/, boost::add_pointer<mpl::_1>, int>::type , int*>)); Handmade apply1 is used instead of mpl::apply. And this example works. What difference? Usage of nested "::type" of apply metafunction. As result: BOOST_MPL_ASSERT((boost::is_same< mpl::apply<apply1<mpl::_1, mpl::_2>::type, boost::add_pointer<mpl::_1>, int>::type , int*>)); doesn't work. Seems like this change affects time of placeholders substitution. Can anybody explain this in detail? So, since apply1 is just simplified version of mpl::apply, why we cannot use mpl::apply w/o "::type"? Because it cannot be compiled, at least using VC8. And seems like the main difference is that apply1 is primary template but mpl::apply is partial template specialization. Is such behavior standard? Can anybody explain the logic? Best regards, Andriy Tylychko, telya(a)mail.ru

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[mpl] pop_back<range_c> is forbidden?
by Andriy Tylychko (mail.ru) 25 Jul '06

25 Jul '06

Hi. Reading "C++ Template Metaprogramming" book: "Though not extensible, range_c supports pop_front and pop_back, because contracting a range is easy" But following code doesn't work (at least using MSVC 8.0): #include <boost/mpl/range_c.hpp> #include <boost/mpl/pop_back.hpp> using namespace boost::mpl; typedef range_c<int, 0, 1> r; typedef pop_back<r>::type p; Can anybody explain? Thank you in advance, Andriy Tylychko, telya(a)mail.ru

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bool_testable / safe bool idiom
by Gottlob Frege 25 Jul '06

25 Jul '06

What ever happened to bool_testable or some other answer to the safe bool idiom? I followed archived emails for a while, but thought it best to just bring up anew. Is a general solution not possible? How about a couple of solutions, where you pick the right one for your case? Or a solution with variations that you pick (policy based)? Anything? Thanks, Tony

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match multiline regular expression
by Winson Yung 25 Jul '06

25 Jul '06

I am trying to match (case insenstive) the following two lines with a single regular expression, but somehow it doesn't work using boot regex: NET INCOME PER COMMON SHARE: Basic .................................................. $ 4.38 $ 3.90 $ 3.37 where: 1) there might be spaces before "NET INCOME PER COMMON SHARE" 2) there might be spaces after "NET INCOME PER COMMON SHARE" 3) the semicolon might be optional ^(\\s*)?Net income per common share:?(\\s*)?\\r\\n( *)?basic Any one has suggestions? /Winson

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version specific "boost-<version>" source header subdirectory
by Noel Yap 25 Jul '06

25 Jul '06

Is there any way _not_ to get the version specific subdirectory? I prefer embedding that information within the --prefix argument. Thanks, Noel

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iterate over key_type of map
by gast128 24 Jul '06

24 Jul '06

Dear all, in our company we use the STL map frequently. However one often wants to iterate over the key_type only (or mapped type, or make desicions for the key type, and take action on its corresponded map type). With the transform_iterator this is possible, but the resulting code is not an improvement over writing the loop explicitly. For example I want to search for the maximum string length: typedef std::map<std::string, double> StringDoubleMap; typedef boost::function<StringDoubleMap::key_type (const StringDoubleMap::value_type&)> Function; typedef boost::transform_iterator<Function, StringDoubleMap::const_iterator> TransformIterator; StringDoubleMap mp = boost::assign::map_list_of("George", 0.0) ("Bill", 0.0) ("Ronald", 0.0) ("Jimmy", 0.0); Function fc = boost::bind(&StringDoubleMap::value_type::first, _1); TransformIterator itBegin(mp.begin(), fc); TransformIterator itEnd(mp.end(), fc); TransformIterator it = std::max_element(itBegin, itEnd, boost::bind (&std::string::length, _1) < boost::bind(&std::string::length, _2)); if (it != itEnd) { std::cout << it->c_str() << ' ' << it->length() << std::endl; } A select1st or select2nd would already a great help. Wkr, me

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Re: [Boost-users] shared_ptr compile error ms vc++ 8
by Andrew McDonald 24 Jul '06

24 Jul '06

you misunderstand....I was answering a prior question posted by bringiton asking how to diagnose the specific source code location of such errors when compiled using vc++ 8... not a question regarding whether or not such code is in error... My posting was an example confirming for bringiton that the error output produced by vc++ 8 specifically also referenced the module/line number that attempted to instantiate the shared_ptr template, rather than just the error location inside the shared_ptr header. Although I am now regretting posting.... ;) regards, Andrew > -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org]On Behalf Of > Bronek Kozicki > Sent: Monday, 24 July 2006 6:37 PM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] shared_ptr compile error ms vc++ 8 > > > Andrew McDonald wrote: > > Was an answer to a previous question regarding locating the > source of the error using vc++ 8 > > >>> When compiling the following line in a file example.cpp; > >>> > >>> boost::shared_ptr<int> p(new std::string) > > you would have error from any compiler, because this code is > illformed. There is > no conversion from std::string* to int* . > > > B. > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users >

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How to detect overflow when use lexical_cast??
by 袁晓辉 24 Jul '06

24 Jul '06

Hi,all I want to cast string to long long type and handle overflow. I tested as follow. long long somevar = lexical_cast<long long>("123456789789789798879977978789787987879879787977897897897899879978798798798");//!!!!!!!!!!!!!! But it does not throw an exception!! It seem that casting to int does not have this kind of problem. int somevar2 = lexical_cast<int>("123456789789789798879977978789787987879");//will throw an exception

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Re: [Boost-users] shared_ptr compile error ms vc++ 8
by Andrew McDonald 24 Jul '06

24 Jul '06

Was an answer to a previous question regarding locating the source of the error using vc++ 8 regards, Andrew > -----Original Message----- > From: boost-users-bounces(a)lists.boost.org > [mailto:boost-users-bounces@lists.boost.org]On Behalf Of > Mateusz Loskot > Sent: Monday, 24 July 2006 5:02 PM > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] shared_ptr compile error ms vc++ 8 > > > Andrew McDonald wrote: > > I am using VC++ 2005 Express Edition v 8.0.050727.42. > > > > When compiling the following line in a file example.cpp; > > > > boost::shared_ptr<int> p(new std::string) > --------------------^^^-------------^^^^^^ > > int type is not a string type, and the other way. > > Best regards > -- > Mateusz Loskot > http://mateusz.loskot.net > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users >

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Re: [Boost-users] shared_ptr compile error ms vc++ 8
by Andrew McDonald 24 Jul '06

24 Jul '06

I am using VC++ 2005 Express Edition v 8.0.050727.42. When compiling the following line in a file example.cpp; boost::shared_ptr<int> p(new std::string) the following error is produced (note the explicit mention of example.cpp(10) ): c:\Projects\boost\shared_ptr.hpp(125) : error C2440: 'initializing' : cannot convert from 'std::string *' to 'int *' Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast .\example.cpp(10) : see reference to function template instantiation 'boost::shared_ptr<T>::shared_ptr<std::string>(Y *)' being compiled with [ T=int, Y=std::string ] regards, Andrew McDonald System Architect Norwood Systems Australia Pty Ltd Level 1, 71 Troy Terrace PO Box 1281 Subiaco, WA 6904 Tel +61 8 9380 7766 Fax +61 8 9380 7733 The information in this email, and any attachments, may contain confidential information and is intended solely for the attention and use of the named addressee (s). It must not be disclosed to any person(s) without authorization. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorized to, and must not, disclose, copy, distribute, or retain this message or any part of it. If you have received this communication in error, please notify the sender immediately.

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