September 2013 - Boost - lists.preview.boost.org

[scope_exit] D-style scope(failure) and scope(success) in C++
by Evgeny Panasyuk 30 Sep '13

30 Sep '13

Hello all, D language has scope(exit), scope(success) and scope(failure) features - http://dlang.org/statement.html#ScopeGuardStatement : "... scope(exit) executes NonEmptyOrScopeBlockStatement when the scope exits normally or when it exits due to exception unwinding. scope(failure) executes NonEmptyOrScopeBlockStatement when the scope exits due to exception unwinding. scope(success) executes NonEmptyOrScopeBlockStatement when the scope exits normally. ..." Andrei Alexandrescu describes some of uses cases for scope(exit), scope(success), scope(failure) at his recent talk : http://channel9.msdn.com/Events/Lang-NEXT/Lang-NEXT-2012/Three-Unlikely-Suc… There is Boost.ScopeExit library which emulates D's scope(exit) via BOOST_SCOPE_EXIT macro, but there are no analogues for D's scope(failure) and scope(success). Current alternative for these features is ScopeGuard idiom ( http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Scope_Guard , http://www.drdobbs.com/cpp/generic-change-the-way-you-write-excepti/1844037… ). Boost.ScopeExit library itself suggests to use ScopeGuard - http://www.boost.org/doc/libs/1_51_0/libs/scope_exit/doc/html/scope_exit/al… : " Boost.ScopeExit is similar to scope(exit) feature built into the D programming language. A curious reader may notice that the library does not implement scope(success) and scope(failure) of the D language. Unfortunately, these are not possible in C++ because failure or success conditions cannot be determined by calling std::uncaught_exception (see Guru of the Week #47 for details about std::uncaught_exception and if it has any good use at all). However, this is not a big problem because these two D's constructs can be expressed in terms of scope(exit) and a bool commit variable (similarly to some examples presented in the Tutorial section). " I have made small library ( https://github.com/panaseleus/stack_unwinding#d-style-scope-guardsactions ) which supplies primitives (class unwinding_indicator, UNWINDING_AWARE_DESTRUCTOR macro) to determining when object destructor is called due to stack-unwinding or due to normal scope leaving. Currently it is implemented on top of platform-specific implementation of uncaught_exception_count function and tested on: {MSVC2005, MSVC2008, MSVC2010, MSVC2012, GCC4.1.2, GCC4.4.6, Clang3.2}x{x32, x64}x{default settings}. uncaught_exception_count is a function similar to std::uncaught_exception from standard library, but instead of boolean result it returns unsigned int showing current count of uncaught exceptions. Such primitives allow us to implement scope(success) and scope(failure) features in C++. I have made several proof-of-concepts: * https://github.com/panaseleus/stack_unwinding/blob/master/examples/scope_ac… * https://github.com/panaseleus/stack_unwinding/blob/master/examples/example_… * https://github.com/panaseleus/stack_unwinding/blob/master/examples/scope_gu… * https://github.com/panaseleus/stack_unwinding/blob/master/examples/boost_sc… boost_scopes.cpp example shows usage of BOOST_SCOPE_FAILURE and BOOST_SCOPE_SUCCESS: try { cout << "Case #1: stack unwinding" << endl; BOOST_SCOPE_EXIT(void) { cout << "exit" << endl; } BOOST_SCOPE_EXIT_END BOOST_SCOPE_FAILURE(void) { cout << "failure" << endl; } BOOST_SCOPE_FAILURE_END BOOST_SCOPE_SUCCESS(void) { cout << "success" << endl; } BOOST_SCOPE_SUCCESS_END throw 1; } catch(int){} { cout << "Case #2: normal exit" << endl; BOOST_SCOPE_EXIT(void) { cout << "exit" << endl; } BOOST_SCOPE_EXIT_END BOOST_SCOPE_FAILURE(void) { cout << "failure" << endl; } BOOST_SCOPE_FAILURE_END BOOST_SCOPE_SUCCESS(void) { cout << "success" << endl; } BOOST_SCOPE_SUCCESS_END } Output is: " Case #1: stack unwinding failure exit Case #2: normal exit success exit " Currently BOOST_SCOPE_FAILURE and BOOST_SCOPE_SUCCESS are implemented based on boost_1_51_0/boost/scope_exit.hpp by copy-paste and replace (just for proof-or-concept, of course it is possible solution with much less duplication). Semantically meaningful changes can be viewed as diff at https://github.com/panaseleus/stack_unwinding/commit/d5513404323490ea99d9b6… Before posting here, I made posts on several C++ forums, but unfortunately get only a few feedbacks regarding ScopeFailure and ScopeSuccess. What do you think? Thank you. P.S. Related discussion: http://lists.boost.org/Archives/boost/2010/09/171051.php Best Regards, Evgeny Panasyuk

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Program Options library and Unicode compliance
by munsingh 30 Sep '13

30 Sep '13

I noticed that the class option_description does not work with wstring, instead works with string. Does anyone has any idea why is it so? Regards, Manish -- May the force be with you

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[clang] How to use CLang for Windows?
by Daryle Walker 30 Sep '13

30 Sep '13

There was a recent conference where the Clang team announced a version of Clang that's supposed to work on Windows (as opposed to kind-of working if you try real hard). It's accessible from the command line if you put Clang in the PATH. I just found out it's supposed to be used from Visual Studio ('10 or '12) after tweaking a project's settings. Can it be used from out BJam system? How will it find right header files to use? (Does it automatically use the ones from MSVC?) Daryle W.

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Code to address the requirement 7(a) of Boost.IOStreams Roadmap
by Gene Panov 29 Sep '13

29 Sep '13

Colleagues, I posted this before, but didn't get answers to some questions so far. I think I possibly addressed the "output" part of requirement 7(a) from the IOStreams Roadmap https://svn.boost.org/trac/boost/wiki/IostreamsRoadmap in this library https://code.google.com/p/async-ostream/ Does it make sense if I create a patch for Boost.IOStreams to add those five files and ask the maintainer (or volunteers) for feedback? Regards, Gene

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[variant] Stalled testing, from missing file.
by Rene Rivera 29 Sep '13

29 Sep '13

Note to the variant maintainers.. I commented out a test which was referring to a non-existent source file. -- -- -- Grafik - Don't Assume Anything -- Redshift Software, Inc. - http://redshift-software.com -- rrivera/acm.org - grafik/redshift-software.com -- 102708583/icq - grafikrobot/aim - grafikrobot/yahoo

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[range][algorithms] How about making the range algorithms pipeable as the range adaptors are?
by Viktor Sehr 28 Sep '13

28 Sep '13

It would be syntactically really nice if the stl-algorithms wrapped in boost range were pipeable, as with the adaptors, making it seamless to combine them in left-to-right statements For non-mutating algorithms I think it's an obvious evolvement const auto& max_pos = some_range | filtered(..) | max_element; const auto& num_elements = some_range | filtered(..) | count(42); ...instead of inside out as it is now const auto& max_pos = max_element(some_range | filtered(..)); const auto& num_elements = count(some_range | filtered(..), 42); For non-mutating algorithms it might not be an obvious solution, as the range beneath is modified, but I still think it should be possible boost::erase(my_vector | sort | unique); ...instead of boost::erase(unique(sort(my_vector)); *Implementation example with std::accumulate:* // Tag to be recognized by the global pipe operatortemplate <typename value_type>struct accumulate_argument_tag { accumulate_argument_tag(const value_type& value) : value_(value) {} const value_type& value_; }; struct accumulate_tag { // Put the regular algorithm as an operator() function where the first argument is the range template <typename range_type, typename value_type> value_type operator()(const range_type& range, const value_type& start) { return std::accumulate(std::begin(range), std::end(range), start); } // If no range is provided, return a tag which contains the argument, which can then be identified by the global pipe operator template <typename value_type> accumulate_argument_tag<value_type> operator()(const value_type& value) { return accumulate_argument_tag<value_type>(value); } };static accumulate_tag accumulate; // Global pipe operator which takes one argumenttemplate <typename range_type, typename value_type>value_type operator|(const range_type& range, const accumulate_argument_tag<value_type>& argument_holder) { return std::accumulate(std::begin(range), std::end(range), argument_holder.value_); } // Global pipe operator which can accept 'accumulate' without any parenthesis// (assuming that std::accumulate can be used without arguments)template <typename range_type>typename range_type::value_type operator|(const range_type& range, const accumulate_tag&) { return std::accumulate(std::begin(range), std::end(range), range_type::value_type(0)); } // Usage std::vector<int> vec;for(size_t i = 0; i < 135; ++i) vec.push_back(i);auto a = accumulate(vec, 0);auto b = vec | accumulate(0);auto c = vec | accumulate; /Viktor

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Borland and metrowerks compiler requirements?
by Stephen Kelly 27 Sep '13

27 Sep '13

Hello, In the work I've done so far on removing ifdefs for obsolete compilers, some compilers which have come up a few times are __BORLANDC__ and __MWERKS__. I have never used either of those compilers. Can old versions of either of them be dropped at this point in boost trunk? Thanks, Steve.

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"Remove obsolete MSVC checks" and _MSC_VER
by Peter Dimov 26 Sep '13

26 Sep '13

One general note about these changes. This: #if defined( _MSC_VER ) && _MSC_VER >= 1310 doesn't mean "compiler is MS VC++ 7.1". It means "compiler claims to support MSVC 7.1's features." Many Windows compilers define _MSC_VER for compatibility. I'm not positive that the removal of the _MSC_VER >= part would break something nowadays, but if it does, this would be why. I'd have left these alone; it's not clear what purpose removing the check is intended to serve, apart from breaking code. Actual MSVC-specific code is guarded by BOOST_MSVC and not _MSC_VER.

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[Container] Memory leak from allocation of 0 sized memory
by Evan Wallace 26 Sep '13

26 Sep '13

I recently tracked down a major memory leak in a system that I am working on to a bug in Boost.Container. The bug is that the following code leaks memory: #include <boost/container/vector.hpp> int main() { while (true) { boost::container::vector<int> vec; boost::container::vector<int> vec2(vec); } } I have submitted a ticket to trac, but since this is a major issue and the release date for 1.55.0 is very soon, I am also posting to the mailing list. https://svn.boost.org/trac/boost/ticket/9166 For reference: the leaked memory is allocated in allocator_version_traits::allocation_command Evan Wallace

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mpl broken after removal of nttp.hpp in 85956
by Jürgen Hunold 26 Sep '13

26 Sep '13

Hi Stephen, the message is: home/hunold/src/devel/boost/boost/mpl/aux_/nttp_decl.hpp:17:42: fatal error: boost/mpl/aux_/config/nttp.hpp: No such file or directory It seems that even nttp_decl.hpp is obsolete, as is only contains: // Obsolete. Remove. # define BOOST_MPL_AUX_NTTP_DECL(T, x) T x /**/ Maybe incomplete quick patch attached. Yours, Jürgen -- * Dipl.-Math. Jürgen Hunold ! * voice: ++49 4257 300 ! Fährstraße 1 * fax : ++49 4257 300 ! 31609 Balge/Sebbenhausen * jhunold(a)gmx.eu ! Germany

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