May 2015 - Boost-users - lists.preview.boost.org

[Multiprecision] Get mantissa of a float
by Leonardo Yvens 04 May '15

04 May '15

Hello, I'm new to the Multiprecision library, and am trying to extract the mantissa from a float. Using cpp_bin_float, it's easy to get the exponent, but how can I get the mantissa in a normalized form (1.xxxxxxxxxx)? I tried messing with the limbs, they contain large powers of two, but I couldn't interpret that. Thank you very much, Leo Y.

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Can a mapped_file bigger than 2GB be random seeked?
by Narcélio Filho 04 May '15

04 May '15

Hello! I'm writting on random positions on a mapped file, but it seems that if I seek past 2GB, write something, then seek to a lower position, I got a segfault. Here is the code: #include <iostream> #include <fstream> #include <boost/iostreams/stream.hpp> #include <boost/iostreams/device/mapped_file.hpp> using namespace std; using boost::iostreams::stream; using boost::iostreams::mapped_file; int main(int argc, char** argv) { const size_t GIGA = 1024l*1024l*1024l; const size_t FILESIZE = 2l * GIGA + 10000; ofstream block("file", ios::binary | ios::out); assert(block.good()); block.seekp(FILESIZE); block.write("", 1); block.close(); mapped_file mappedFile("file"); stream<mapped_file> file(mappedFile, ios::binary | ios::out); assert(mappedFile.is_open()); char buffer[10] = {0}; cout << 0 << endl; file.seekp(0); file.write(buffer, 1); cout << FILESIZE - 1 << endl; file.seekp(FILESIZE - 1); file.write(buffer, 1); cout << 1 * GIGA << endl; file.seekp(1 * GIGA); file.write(buffer, 1); return 0; } I compile and run on Ubuntu 14.10/amd64: $ g++ example.cpp -lboost_iostreams 0 2147493647 Segmentation fault (core dumped) I also get the same error on Windows 8/amd64. What I'm doing wrong? []s, Narcélio.

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[c++now] Perhaps of interest to Boost library users
by Niall Douglas 03 May '15

03 May '15

https://plus.google.com/+nialldouglas/posts/DsAdUV4RgY5 Content of post for convenience: Just finished my C++ Now 2015 presentation with exactly one week to go! Currently 90 slides for a 90 minute long presentation, I had originally been worried I'd be boring but I think, even if I do say so myself, that this will be one of the more interesting talks at C++ Now this year. It reviews *ten* C++ 11/14 only libraries close to entering Boost, three of which in detail (Boost.AFIO, Boost.Fiber, Boost.DI) and one in very great detail (Boost.APIBind), indeed I spend about 45 slides on APIBind as I believe it provides the foundation stone for a fully modular C++ 11 only Boost 2.0 branch with very significant improvements over Boost 1.0. I also draw some sweeping personal general opinions from the ten library review, and I'll try to answer these questions: * Why do these libraries require C++ 11 or 14? From an end user perspective. * Is there a common theme of the most popular C++ 11/14 features used? * Is there a common theme in choice of library design and use of third party libraries? * Are there techniques used in one library which would make a lot of sense to be used in another library, but for some reason are not? * Do these new libraries take notice of one another and integrate themselves well with other libraries, or are they ivory towers? * How many of these forthcoming libraries explicitly seek to contribute to future C++ standardization? Boost only a few years ago was in a state of sickly malaise after the exit of several big names who had dominated it since its inception. Indeed, in 2013 no new libraries had entered in two years, and nobody could say if Boost was going to be the venue for the next generation of C++ 11/14 libraries approaching standardisation or whether some other venue (especially WG21 itself) would take over. Since 2013 *seventeen* new libraries have either entered Boost or entered the formal review queue, almost a third of which are C++ 11/14 mandatory libraries, whilst WG21's efforts to invent new libraries have not panned out well to date. Traffic on the Boost mailing lists which had become anaemic has once again returned to mass-delete-without-reading levels. It looks like Boost is going to remain the place to be for the highest quality C++ libraries, especially those intended for eventual standardisation. The big question is whether the C++ 11/14 mandatory libraries are so different from the 98/03 libraries in design and philosophy that a C++ 11/14 only Boost 2.0 distribution is warranted? Robert Ramey will be presenting on his vision for Boost 2.0 at C++ Now 2015, and he kindly has allowed me to add my ha'pennies worth after he finishes during which I will summarise my empirical findings from the ten library review. So watch out for the recorded videos! -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/

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[BGL] I think the invariant in ResourceExtensionFunction for r_c_shortest_paths is not correct
by Alberto Maria Santini 02 May '15

02 May '15

The documentation for 1.58.0 (http://www.boost.org/doc/libs/1_58_0/libs/graph/doc/r_c_shortest_paths.html) correctly states that: >>> The implementation is a label-setting algorithm. This means that there must be one or more resources whose cumulated consumption(s) after extension is/are always at least as high as before. This is similar to the Dijkstra algorithm for the SPP without resource constraints where the distance measure must be non-negative. It is sufficient if there is one resource with a non-negative resource consumption along all arcs (for example, non-negative arc lengths or non-negative arc traversal times). >>> But, later on, it says: >>> If ref models the ResourceExtensionFunction concept, and if the type Resource_Container models the ResourceContainer concept, after the call ref( const Graph& g, Resource_Container& new_cont, const Resource_Container& old_cont, graph_traits<Graph>::edge_descriptor ) the expression old_cont <= new_cont evaluates to true. This is because, as stated above, the implementation is a label-setting algorithm. Therefore, the Less-Than operator for ResourceContainer must compare one or more resource(s) whose resource consumption(s) along any arc is/are non-decreasing in order for the algorithm to work properly. >>> Now, saying that "old_cont <= new_cont" is much stricter than it should be. The correct requirement (first quote) is that there is **at least one** resource whose consumption monotonically doesn’t decrease. What "old_cont <= new_cont” requires, is that **all** resources’ consumptions are monotonically non-decreasing. These two things are equivalent iff the label only has one resource. Can someone confirm that my observation makes sense? In this case, I’ll open a ticket and submit a patch for the documentation. Can someone also confirm that this check is *not* enforced in r_c_shortest_paths.hpp? Thanks, AS

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Official Stance on CMake Adoption
by Michael Ainsworth 02 May '15

02 May '15

What is the official stance on CMake adoption? Is if simply a fork in the development, or will all of Boost eventually be built using CMake? Michael

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Re: [Boost-users] [boost] [ANN] "Die Boost C++ Bibliotheken", 2nd edition available (German edition)
by Rüdiger Berlich 01 May '15

01 May '15

Let me just say that the book is excellent! Thanks, Boris, for supplying such a comprehensive source of information on Boost. Best Regards, Ruediger > Am 01.05.2015 um 12:31 schrieb Boris Schäling <boris(a)highscore.de>: > > Just a quick announcement: The 2nd edition of my book "Die Boost C++ Bibliotheken" (German edition) is available. > > - It introduces 72 Boost libraries. > - It contains more than 430 examples. > - The print version has 600 pages. > - There is also a Kindle, Epub and PDF version. > - It's also online: <http://dieboostcppbibliotheken.de/> > > There is hardly any difference between the German and the English language edition. The German language edition is a bit more up-to-date after the English language edition has been published in September last year. But there is no need to read the book again in case you read the English language edition already. > > For those who don't know German: The English language edition remains available online at <http://theboostcpplibraries.com/>. > > Boris > > > _______________________________________________ > Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

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Boost.Cgi Status
by Michael Ainsworth 01 May '15

01 May '15

What is the status of Boost.Cgi by Darren Garvey? It seems that the library hasn't been accepted and it's now 2015 - at least 7 years after last Boost Users mailing list post regarding its status. Michael

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