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

[mpi] Boost.MPI and MPI 3!
by Renato Forti 01 Apr '13

01 Apr '13

Hi All, Boost.MPI project will support MPI version 3 with that provide some support to fault tolerance! Have any work in this area? Thanks

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Associative container using a vector
by Stefan Strasser 01 Apr '13

01 Apr '13

Hi everyone, I often find myself using a specific data structure and I'm wondering whether: - it has a wellknown name - there is a generic equivalent in a boost library - or there is interest to add one. The basic idea is that you have a bunch of values stored in one object of type A: struct A{ vector<Value> values; }; and then you have multiple objects of type B that each have to associate data with each value stored in A. you could use: struct B{ map<Value,Data> data; }; but since A::values already provides a contiguous index for the values you can just as well store the data in B in a vector with matching indexes, and make sure that the indexes used in A::values don't change: struct A{ vector<Value> values; vector<std::size_t> freelist; map<Value,std::size_t> index; void erase(...){ push index of unused value to freelist; } void push_back(Value){ reuse a freelist entry or values.push_back; } }; struct B{ vector<optional<Data> > data; }; keep in mind that there is one object A for many objects B. you can now access the associated data of many objects B by looking up the index once in object A, and by wasting some space in B::data for unused entries: b.data[a.index[value]] If Data is a pointer or any other type that knows an empty() state, you can also get rid of optional<> and generalize it as two template like: template<class Value> class index; template<class Mapped,class OptionalTraits=boost_optional_traits> class vector_map; Is there anything like that?

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[config] BOOST_NOEXCEPT on MSVC
by Michael Marcin 01 Apr '13

01 Apr '13

Why isn't BOOST_NOEXCEPT defined to be throw() for msvc? Microsoft Visual Studio 11.0\VC\include\yvals.h defines: #define _NOEXCEPT throw () and the rest of the standard library implementation uses it ex. void swap(thread& _Other) _NOEXCEPT { // swap with _Other _STD swap(_Thr, _Other._Thr); } http://msdn.microsoft.com/en-us/library/wfa0edys.aspx states: throw() The function does not throw an exception. However, if an exception is thrown out of a function marked throw(), the Visual C++ compiler will not call unexpected (see unexpected (CRT) and unexpected (<exception>) for more information). If a function is marked with throw(), the Visual C++ compiler will assume that the function does not throw C++ exceptions and generate code accordingly. Due to code optimizations that might be performed by the C++ compiler (based on the assumption that the function does not throw any C++ exceptions) if a function does throw an exception, the program may not execute correctly. It seems a better choice here than expanding BOOST_NOEXCEPT to nothing.

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Re: [boost] [fusion] What do we do with nil ?
by Enrique Nieloud 31 Mar '13

31 Mar '13

Hi!, Sorry to bother, but is is patch officially included in version 1.53.0? I'm having trouble to compile under XCode 4 and it seems related to the "nil" word. thanks, - Enrique

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Re: [boost] Review managers wanted for augmented data structures
by Dave Abrahams 31 Mar '13

31 Mar '13

on Mon Mar 04 2013, Vadim Stadnik <vadimstdk-AT-gmail.com> wrote: > On Mon, Mar 4, 2013 at 7:35 PM, Stefan Strasser <strasser(a)uni-bremen.de>wrote: > >> Am 04.03.2013 08:48, schrieb Martin Knoblauch Revuelta: >> >> Do you mean that you would declare them RandomAccess iterators? >>> >>> We can expect to have containers with millions of elements. For that >>> size, O(log N) is about 20 times faster than O(log N log N). That >>> makes a big difference. >>> >> >> isn't that a reason for providing optimized specializations of some STL >> algorithms, instead of introducing another iterator category? >> >> how would a new iterator category even help? >> as long as your iterator is a forward iterator, the user is allowed to >> call std::binary_search on your iterator, which uses the same algorithm on >> any iterator category. (only functions used by binary_search like >> std::advance are specialized on the category) >> where in all this would your tree-optimized binary_search code be called? >> >> the standard doesn't require random access iterator ops to be constant >> time. >> >> > Unfortunately, there is a problem of iterator categories with augmented > trees. The C++ standard specifies computational complexity for iterator > operations, although they are not shown in tables, since all of them are > required to be constant time. In both C++03 and C++11 this is formulated in > the section 24.1.8. Are you sure these iterators don't fall under the *amortized* constant time requirements, just like those of the ordered associative containers? -- Dave Abrahams

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[gil] undocumented/unintended concept requirements in color_convert
by Michael Marcin 31 Mar '13

31 Mar '13

I was trying to add other color spaces support and noticed that the rgb to cmyk converter contains: typedef typename channel_type<P2>::type T2; T2 x = channel_traits<T2>::max_value()-get_color(dst,black_t()); if (x>0.0001f) { float x1 = channel_traits<T2>::max_value()/float(x); T2 should model: http://www.boost.org/doc/libs/1_53_0/libs/gil/doc/html/g_i_l_0264.html but this code additionally requires T2 to be greater-than comparable to float and convertible to float.

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Re: [boost] [exception] uncaught_exception_count, scope(failure), scope(success)
by Evgeny Panasyuk 31 Mar '13

31 Mar '13

>06.02.2013 2:57, Emil Dotchevski: >>> While scope(exit) is some kind of ad-hoc replacement for RAII wrappers, >>> scope(failure) and scope(success) are not. >>> Nowadays scope(failure) and scope(success) are emulated in C++ via >>> ScopeGuard idiom. >> >> Could you clarify what does uncaught_exceptions_count() use look like? >> How is it different scope guard? > > [skipped] There is proposal by Herb Sutter for add similar functionality to ISO - std::unwinding_exception http://isocpp.org/blog/2013/03/n3614-unwinding-exception , http://isocpp.org/files/papers/N3614.pdf which is aimed on providing basis for implementation of scope(failure)/scope(success). Emil, could you please clarify what is your position on adding uncaught_exception_count into Boost.Exception? ( https://github.com/panaseleus/stack_unwinding/blob/master/boost/exception/u… ) -- Evgeny Panasyuk

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Experimenting with modular Boost
by Jonathan Wakely 30 Mar '13

30 Mar '13

The instructions at https://svn.boost.org/trac/boost/wiki/TryModBoost seem to be bogus, apparently because the cloned repo contains no .gitmodules file so the 'git submodule update --init' command does nothing, and I then get an error for the last step: $ cmake -P forward_headers.cmake CMake Error: Error processing file:forward_headers.cmake I'm "only" using Git 1.7.12 but I don't think that's the problem. The older instructions at https://svn.boost.org/trac/boost/wiki/CMakeModularizationStatus refer to a non-existent http://github.com/boost-lib/boost URL, so they don't work either. I've looked at several other wiki pages, but they're also inconsistent or don't help. Is there any accurate documentation for modular Boost? How does someone try modular boost?

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[Filesystem] v3 path separator changes
by Alexander Lamaison 30 Mar '13

30 Mar '13

I'm finally getting round to moving to Filesystem v3 and now my code is breaking all over the place. The cause is the output of string() on Windows which has changed behaviour. I'm manipulating Unix paths for use over SFTP, but doing so on Windows. For instance I might want to append "c" to the Unix path "/a/b". path p("/a/b"); p /= "c"; cout << p.string(); In version 2 this would output "/a/b/c" but now it produces "/a/b\c". Why the breaking change? I'm trying to understand the rationale behind many of the v3 changes which [1] and [2] don't even begin to cover. [1] http://www.boost.org/doc/libs/1_53_0/libs/filesystem/doc/v3.html [2] http://www.boost.org/doc/libs/1_53_0/libs/filesystem/doc/deprecated.html Alex -- Swish - Easy SFTP for Windows Explorer (http://www.swish-sftp.org)

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[switch generator] status
by Jeff Flinn 29 Mar '13

29 Mar '13

Does anyone know the current status of Steven's switch generator library, I see it was reviewed/accepted in 2008, but I don't see it in trunk or any release. Thanks, Jeff

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