July 2018 - Boost - lists.preview.boost.org

[range] [concepts] Boost 1.68 beta build error in RandomAccessIteratorConcept using latest MSVC
by Viktor Sehr 20 Jul '18

20 Jul '18

The following error is emitted in latest MSVC building Boost 1.68 beta: 1>\boost\range\concepts.hpp(257): error C3646: 'n': unknown override specifier 1>\boost\range\concepts.hpp(264): note: see reference to class template instantiation 'boost::range_detail::RandomAccessIteratorConcept<Iterator>' being compiled 1>\range\concepts.hpp(257): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int Unfortunately I'm not competent enough to determine what is causing the error: Full struct: template<class Iterator> struct RandomAccessIteratorConcept : BidirectionalIteratorConcept<Iterator> { #if BOOST_RANGE_ENABLE_CONCEPT_ASSERT BOOST_RANGE_CONCEPT_ASSERT(( Convertible< BOOST_DEDUCED_TYPENAME RandomAccessIteratorConcept::traversal_category, random_access_traversal_tag >)); BOOST_CONCEPT_USAGE(RandomAccessIteratorConcept) { i += n; i = i + n; i = n + i; i -= n; i = i - n; n = i - j; } private: // MSVC 14.1 - avoid C4596: 'difference_type': illegal qualified name in member declaration #if defined(_MSC_VER) && _MSC_VER >= 1912 BOOST_DEDUCED_TYPENAME difference_type n; #else BOOST_DEDUCED_TYPENAME RandomAccessIteratorConcept::difference_type n; #endif Iterator i; Iterator j; #endif }; br/Viktor Sehr

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[system] Clang CI builds broken because of constexpr
by Andrey Semashev 20 Jul '18

20 Jul '18

Hi, I'm seeing these errors in Travis CI builds with Clang 3.8, 3.9, 4.0 and 5.0: ./boost/system/error_code.hpp:232:41: error: constexpr constructor never produces a constant expression [-Winvalid-constexpr] BOOST_SYSTEM_CONSTEXPR explicit std_category( boost::system::error_category const * pc ): pc_( pc ) ^ ./boost/system/error_code.hpp:232:41: note: non-constexpr constructor 'error_category' cannot be used in a constant expression /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/system_error:69:5: note: declared here error_category() noexcept; ^ I'm assuming this is because the compiler uses libstdc++ from gcc 4.8, in which error_category() is not marked constexpr. Can this be fixed somehow?

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Looking for help on preparing for review
by Damian Vicino 20 Jul '18

20 Jul '18

Hi, I'm preparing my library safe_float to be proposed for review. The library was born in the GSOC2015, but it never reached a review ready state. My plan is to change that in the next few months. At this point, I'm looking for some volunteers to proof-read the documentation. Code is going through major rewrite, and I will send another mail looking for help with reviewing the code when that is done. The most current documentation can be read directly from the web here: https://sdavtaker.github.io/safefloat/ Any comment is appreciated. Best regards, Damian

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[Compute] Conflict between boost::compute::zip_iterator and boost::iterators::zip_iterator
by fortenberry.rm＠protonmail.com 18 Jul '18

18 Jul '18

I'd like to use boost::compute and boost::range together, like below, but if I uncomment the '#include <boost/range/combine.hpp>' line I get an error saying that boost::compute::zip_iterator and boost::iterators::zip_iterator are ambiguous. Is there a way around this, so that I can use boost::compute and boost::range together in the same cpp file? I am using on Windows vs2015 64bit. Boost 1.67.0. Code: #include <vector> #include <iostream> #include <algorithm> //#include <boost/range/combine.hpp> #include <boost/compute/lambda.hpp> #include <boost/compute/functional/math.hpp> #include <boost/compute/container/vector.hpp> #include <boost/compute/algorithm/transform.hpp> namespace compute = boost::compute; using compute::float4_; using compute::lambda::_1; using compute::lambda::_2; using compute::lambda::distance; int main() { // get default device and setup context compute::device device = compute::system::default_device(); compute::context context(device); compute::command_queue queue(context, device); // generate random data on the host std::vector<float4_> a(10000); std::vector<float4_> b(10000); std::vector<float> r(10000); std::generate((float*)a.data(), (float*)(a.data() + a.size()), rand); std::generate((float*)b.data(), (float*)(b.data() + b.size()), rand); // create a vector on the device compute::vector<float4_> _a(a.size(), context); compute::vector<float4_> _b(b.size(), context); compute::vector<float> _r(r.size(), context); // transfer data from the host to the device compute::copy(a.begin(), a.end(), _a.begin(), queue); compute::copy(b.begin(), b.end(), _b.begin(), queue); boost::compute::transform( _a.begin(), _a.end(), _b.begin(), _r.begin(), distance(_1, _2), queue ); // copy values back to the host compute::copy(_r.begin(), _r.end(), r.begin(), queue); for (int i = 0; i < a.size(); ++i) { float4_ va = a[i]; float4_ vb = b[i]; float vr = r[i]; float e = std::sqrt(std::pow(va[0] - vb[0], 2) + std::pow(va[1] - vb[1], 2) + std::pow(va[2] - vb[2], 2) + std::pow(va[3] - vb[3], 2)); std::cout << std::setprecision(12); if (std::abs(e - vr) > 1e-2) std::cout << e << " != " << vr << "\n"; } return 0; } Error, truncated for brevity. I can post the full error log if it is helpful: 1>------ Build started: Project: demo, Configuration: Debug x64 ------ 1> demo.cpp 1> This header is implementation detail and provided for backwards compatibility. 1>C:\local\boost_1_67_0\boost/compute/algorithm/transform.hpp(67): error C2668: 'boost::compute::make_zip_iterator': ambiguous call to overloaded function 1> C:\local\boost_1_67_0\boost/compute/iterator/zip_iterator.hpp(276): note: could be 'boost::compute::zip_iterator,boost::compute::buffer_iterator,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>> boost::compute::make_zip_iterator,boost::compute::buffer_iterator,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type,boost::tuples::null_type>>(IteratorTuple)' 1> with 1> [ Thanks, Madison

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[boostbook] cleanup / modernization
by James E. King III 18 Jul '18

18 Jul '18

I would have opened an "issue" on the boostorg/boostbook project, however, that is not enabled. (Perhaps someone should enable it?) I have duplicated the boostbook setup scripts into the docker setup environment for Ubuntu Bionic and I have found that all of the packages that boostbook depends on are ancient. PackageVersionLast ModifiedHost docbook-xsl 1.75.2 2009 SourceForge <http://sourceforge.net/projects/docbook/files/docbook-xsl/1.75.2/docbook-xs…> docbook-xml 4.2 2002 oasis-open.org <http://www.oasis-open.org/docbook/xml/4.2/docbook-xml-4.2.zip> fop 0.94 2007 Apache <http://archive.apache.org/dist/xmlgraphics/fop/binaries/fop-0.94-bin-jdk1.4…> These tools are quite old and it is only a matter of time before the older versions could be removed. These external sites are under no particular requirement to keep these older versions of software available. At some point some of these tools may no longer work with current operating system tools, for example "fop" says that it is for "JDK 1.4". Each of these tools has a newer version. A project should be initiated now to modernize the documentation build to use more recent versions of these tools before it becomes a critical release blocker at a bad time. - Jim

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[iostreams] libstdc++ vs MSVC exception handling behavior in seekg, seekp
by James E. King III 17 Jul '18

17 Jul '18

I found a disabled test in Boost.Iostreams called stream_state_test. It was disabled because it was thought it only tests the standard library implementation. Partially true, but it also tests some parts of iostreams so I have been working to re-enable it along with the generic CI upgrades. It looks like libstdc++ and the standard library that comes with MSVC (is it still Dinkumware? It used to be...) handle exceptions on stream seekg and seekp differently. I haven't consulted the standards documents yet, but I found this reference for exception handling: http://www.cplusplus.com/reference/istream/istream/seekg/ which states, " Any exception thrown by an internal operation is caught and handled by the function, setting badbit <http://www.cplusplus.com/ios_base::badbit>. " Sitting in the debugger where the test throws an exception in error_device::seek, there is no exception handling within iostreams or in msvcp140d code paths for a call to seekg, while the libstdc++ implementation is able to pass all of the tests. This leads to a couple questions: 1. Are the standards clear in this area? 2. Is someone violating them? A cursory review (such as this) leads me to believe that the MSVC C++ runtime implementation is not properly handling exceptions here. The sources for seekg in libstdc++ wrap the internals in a try catch in order to restore state. The sources for seekg in the MSVCPRT do not. - Jim

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Safe Float design question
by Damian Vicino 17 Jul '18

17 Jul '18

Hi, I looking for some design advice. The context: - I'm revisiting SafeFloat after some time and, while doing so, I'm rethinking all the decisions from the past. Idea is to sent for review in the following months. - The goal of the library is being a drop-in replacement for float, that adds checks to floating point operations and reports when a check failed. Without SafeFloat, someone could write something like this: #include <iostream> #include <limits> #include <cfenv> using namespace std; int main(){ float a = 1.0f; float b = numeric_limits<float>::max(); feclearexcept(FE_ALL_EXCEPT); float c = a/b; if(fetestexcept(FE_UNDERFLOW)) { cout << "underflow result\n"; } } What I expect when using safe_float is to declare upfront "what checks" I care about, "what operations" to check, and "what to do when a check fails". Some intention examples: - I would like to check there was no "overflow_to_infinite" in "addition operations", otherwise I "throw exception".. - I would like to check there was no "division by zero" in "division", otherwise I will "log to cerr and ignore it". - I would like to check there was no "inexact" "addition", otherwise I return an boost::unexpected. I have at least 5 things to check (there is 5 flags in c++11::fenv). I have at least 4 places to check (+/-/*//) and I want to keep what to do about it customizable. In addition, sometimes I want to check multiple things "overflow and underflow", etc... So, the question is how the user can pass all that information to the type and it doesn't look as horrible nonsense. My original option was: int main(){ using CHECK = compose_policy<check_addition_overflow, check_division_by_zero, check_division_underflow>::type; using REPORT = report_throw_on_failure; using sf = safe_float<float, CHECK, REPORT>; try{ sf a = 1.0_sf; sf b = numeric_limits<sf>::max(); auto c = a/b; } catch (safe_float_exception e){ cout << e.message(); //this outputs there was a underflow } } Please comment in what you think about this way to use. Is there a better way to specify the policies to apply that I should try? Best regards, Damian I expect when using safe float to write some code like this: int main(){ safe_float<float> }

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[system] Clang CI builds broken because of constexpr
by Andrey Semashev 17 Jul '18

17 Jul '18

Hi, I'm seeing these errors in Travis CI builds with Clang 3.8, 3.9, 4.0 and 5.0: ./boost/system/error_code.hpp:232:41: error: constexpr constructor never produces a constant expression [-Winvalid-constexpr] BOOST_SYSTEM_CONSTEXPR explicit std_category( boost::system::error_category const * pc ): pc_( pc ) ^ ./boost/system/error_code.hpp:232:41: note: non-constexpr constructor 'error_category' cannot be used in a constant expression /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/system_error:69:5: note: declared here error_category() noexcept; ^ I'm assuming this is because the compiler uses libstdc++ from gcc 4.8, in which error_category() is not marked constexpr. Can this be fixed somehow?

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[graph] disjoint_sets
by James E. King III 17 Jul '18

17 Jul '18

Hello folks in the Boost.Graph team, The CMT currently maintains Boost.DisjointSets which contains a class that is only used by Boost.Graph and Boost.GraphParallel. The headers are published in "boost/pending" right now. Given the CMT has a considerable workload already I would like to discuss moving disjoint_sets into Boost.Graph, as long as it satisfies the requirements for the two repositories currently consuming it. This would be for 1.69.0. Any thoughts, objections, considerations on this (open to anyone)? Thanks, Jim

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Heads up about future standards annexing new identifiers
by Marshall Clow 16 Jul '18

16 Jul '18

As facilities get added to the standard library, they need names. When this happens, it restricts what other developers can and cannot do in their programs. For example, one cannot do this and expect most anything in the standard library to work: #define allocate(T) . new T [ But you knew about that ]. What you may not have known about was that the standards committee has voted contract enforcement/checking facilities into the draft standard (which will probably be C++20). This includes attributes named: 'expects' and 'ensures'. (all lower case) I have checked all of boost, and with the possible exception of Boost.Contract, we do not have any macros with those names. But you might want to keep your eyes open. -- Marshall P.S. These are not keywords - so it's perfectly fine to have member functions with these names. Variables, too. Probably even free functions - though I haven't tried that. But macros are right out ;-) P.P.S. For people who are interested, the paper is http://wg21.link/P0542

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