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Boost Variant Type Interfaces
by Ali Nakipoglu 09 Feb '16

09 Feb '16

Hi, In our project we are using boost, boost.variant very extensively. We was using methods provided by the library to interface with Variant types. Mainly : get<T>( variant ) for accessing stored values and variant.which() == Index for checking currently stored type. Overtime we realized we can improve this as : variant.getT() for accessing stored values much more nicer to write and variant.isT() or variant.which() == WHICH_T for checking currently stored type which does not depend on order of template paramters in the Variant definition. Also in some cases we wanted to be able to add type specific methods for example in our case we are using subscript operator to access recursively stored Variants variant[ "a" ].isT() or variant[ 0 ].asT() We generalized this solution for our project and published at https://github.com/FictionIO/WrappedVariant I would like to hear your comments. Do you think its a correct approach or useful? Any suggestions are welcome! Kind Regards, Ali

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[Multiprecision] Runtime assertion failure with clang++3.6.0 but not g++4.9.2
by mbw_bst＠mailbox.org 09 Feb '16

09 Feb '16

Dear all, this is my first post on this mailing list, so hopefully this will all be by the book. Executing the following minimal working example, which is supposed to calculate "3! == 6" via (1) a template function (2) a class template and save the result in a boost::multiprecision::mpz_int, results in unexpected behavior for clang++3.6.0, with the version of my boost library being 1.59.0. The program displays the correct result using g++4.9.2 however: #include <iostream> #include <boost/multiprecision/gmp.hpp> namespace bm = boost::multiprecision; template <std::size_t N> bm::mpz_int factorial() { return N * factorial<N-1>(); } template<> bm::mpz_int factorial<0>() { return 1; } template <std::size_t N> struct factorial2 { static const bm::mpz_int value; }; template<std::size_t N> const bm::mpz_int factorial2<N>::value = N * factorial2<N-1>::value; template<> struct factorial2<0> { static const bm::mpz_int value; }; const bm::mpz_int factorial2<0>::value = 1; int main () { std::cout << factorial<3>() << '\n'; std::cout << factorial2<3>::value << '\n'; return 0; } The output for clang, having been compiled via clang++ -std=c++14 -stdlib=libc++ -DNDEBUG -o main main.cpp -lgmp will result in: 6 0 However, omitting the NDEBUG flag will trigger an assertion failure: main: /usr/include/boost/multiprecision/gmp.hpp:1296: const mpz_t &boost::multiprecision::backends::gmp_int::data() const: Assertion `m_data[0]._mp_d' failed. Aborted (core dumped) Compiling the same program with g++4.9.2 (with or without "-DNDEBUG") yields the expected result: 6 6 What did I miss? Can this behavior indeed be traced down to Boost.Multiprecision, or does it have to do with the initialization order of static const class members? Or something else? Additionally, both variants work correctly with clang when using a built-in type like 'int'. Any help in understanding the problem on hand would be greatly appreciated! Best Regards, mbw

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Re: [Boost-users] [Multiprecision] Runtime assertion failure with clang++3.6.0 but not g++4.9.2
by mbw_bst＠mailbox.org 09 Feb '16

09 Feb '16

Hello again and thanks for your replies! Taking the following two statements into account: > For type int, the values are computed recursively at compile time, for a > user-defined-type the values are computed at runtime and you hit > initialization-order issues. > Seems to be that Multiprecision relies on static data that haven't > (necessarily) been initialized before your own static members. Works > fine > if the members are made non-static: Does that mean that, since a) boost::multiprecision::number<gmp_int> is not constexpr enabled, and b) static initialization can't happen at compile-time for user-defined types, that there is no way for me to initialize a variable of this type at compile-time? Does b) follow logically from a) ? I (believe to have) confirmed runtime-initialization by running valgrind, which showed the presence of dynamic memory allocations (and also jumps depending on uninitialized variables, which probably corresponds to the assertion failure). I am mentioning this because initially my little test program looked somewhat like this: #include <iostream> #include <vector> #include <boost/multiprecision/gmp.hpp> namespace bm = boost::multiprecision; template<std::size_t N> struct factorial { static const bm::mpz_int value; static void add_values(std::vector<bm::mpz_int>& vec) { factorial<N-1>::add_values(vec); vec.push_back(value); } }; template<std::size_t N> const bm::mpz_int factorial<N>::value = N * factorial<N-1>::value; template<> struct factorial<std::size_t{0}> { static const bm::mpz_int value; static void add_values(std::vector<bm::mpz_int>& vec) { vec.push_back(value); } }; const bm::mpz_int factorial<0>::value = 1; int main () { std::vector<bm::mpz_int> fac_table{}; factorial<10'000>::add_values(fac_table); std::cout << "Enter a number between 0 and 10'000 to calculate factorial:"; std::size_t number; std::cin >> number; std::cout << '\n' << number << "! == " << fac_table[number] << '\n'; return 0; } This still includes the "unsafe" static initialization of a user-defined type. However it compiles and runs via g++ -ansi -std=c++14 -O3 -Wall -Wextra -pedantic -static -save-temps -ftemplate-depth-50000 -DNDEBUG -o main main.cpp -lgmp -pthread This was what made me believe in the compile-time computation of the factorials in the first place, since using this version, valgrind does not show any dynamic memory allocation at all. On the other hand, I don't understand what's going on here really, especially since std::vector<> is supposed to allocate memory at run-time. Now I'm not sure whether the last example has anything to do with Boost.Multiprecision anymore, so while it would really make my day if you could help me better understand this, I will understand if this is not the right place to ask these questions. Thanks again for your replies so far, they have been of great help! Cheers, Max

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[gsoc16] ATTN: Project ideas deadline 19th Feb
by Niall Douglas 07 Feb '16

07 Feb '16

Tomorrow 8th February the application period for Google Summer of Code 2016 begins, and yet we have just *one* idea on the ideas page: https://svn.boost.org/trac/boost/wiki/SoC2016 We need *plenty* more if we are to be approved again this year as a Google Summer of Code org, the deadline for which is the 19th February. So if you have some project ideas and think you could mentor a student this summer, *please* consider adding a project idea to the ideas list or stepping forward with a list of Boost libraries or topics you'd be willing to mentor. Our thanks in advance. --- Boost C++ Libraries Google Summer of Code 2016 admin https://svn.boost.org/trac/boost/wiki/SoC2016

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download from sourceforge?
by Dan Bloomquist 07 Feb '16

07 Feb '16

I followed the link form boost.org and then through sourceforge. But sourceforge directed me to: <http://downloadbud.com/?adprovider=sourceforge_fwint&source=fw36_300x250-do…> The link is an executable! I've never heard of 'downloadbud'. Not a big deal for now, I'm running with 1.58. But I'd like to get the latest of spirit x3 before I ask questions on the spirit list that may not need asking. Is there another source for boost? Or, is this executable actually a safe extractor? Sourceforge handing over an exe when it should be be a package seems just wrong... Thanks, Dan.

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Boost and v8
by Daniel Burchardt 06 Feb '16

06 Feb '16

Hi, I try create v8 module to python used boost and i have problem: #include <iostream> using namespace std; #include <stdio.h> #include <stdlib.h> #include <string.h> #include "include/libplatform/libplatform.h" #include "include/v8.h" using namespace v8; const char* say_hello(const char* name) { return name; } #include <boost/python/module.hpp> #include <boost/python/def.hpp> #include <boost/python/class.hpp> using namespace boost::python; BOOST_PYTHON_MODULE(hello) { class_<V8, boost::noncopyable>("V8", no_init) .def("Initialize", &V8::Initialize).staticmethod("Initialize"); def("say_hello", say_hello); } compile process is ok but when i try import hello in python i see error: /hello.so: undefined symbol: _ZN2v82V810InitializeEv Thanks for help

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[MSM][MPL] Can't compile FSM with > 20 transitions (solved)
by Carlos Santos 05 Feb '16

05 Feb '16

Hi there, I am using boost v1.59 and I am having trouble in compiling a MSM state machine with more than 20 transitions. I followed the Q&A and added the following lines BEFORE any boost include: #define BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS #define BOOST_MPL_LIMIT_VECTOR_SIZE 30 // or whatever you need #define BOOST_MPL_LIMIT_MAP_SIZE 30 // or whatever you need but now instead of getting the previous error: error: wrong number of template arguments (21, should be 20) I get this one: /usr/local/include/boost/multi_index/tag.hpp:75:67: error: wrong number of template arguments (30, should be 20) mpl::vector<BOOST_PP_ENUM_PARAMS(BOOST_MULTI_INDEX_TAG_SIZE,T)>, I was just finishing this email when I found a solution. Adding only the following header #include "boost/mpl/vector/vector30.hpp" and explicitly declaring the transition table as a numbered mpl::vector (yep you have to count the rows...) struct transition_table : mpl::vector21< ... > solves the problem. Can you suggest me a better solution for this? Thanks! *Carlos Santos *

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[Test] BOOST_CHECK_EQUAL can't compare scoped enumerations
by Merrill Cornish 05 Feb '16

05 Feb '16

I'm running Windows 10, 64-bit, MinGW64 with GCC 5.3 64-bit, and BOOST_1_60_0 64-bit. Here is the stripped down version of what's failing: enum class UsedFor { NOTIFY_INPUT, CONST_INPUT, VAR_INPUT, NOTIFY_RESULT, VAR_RESULT}; UsedFor mUse = UsedFor::NOTIFY_INPUT; BOOST_CHECK(mUse == Operand::UsedFor::NOTIFY_INPUT); // BOOST_CHECK_EQUAL(mUse, Operand::UsedFor::NOTIFY_INPUT); If BOOST_CHECK_EQUAL() is commented out, BOOST_CHECK() complies and executes without error. However, // BOOST_CHECK(mUse == Operand::UsedFor::NOTIFY_INPUT); BOOST_CHECK_EQUAL(mUse, Operand::UsedFor::NOTIFY_INPUT); If BOOST_CHECK() is comment out, BOOST_CHECK_EQUAL() gets a template barf with the general comment, " template argument deduction/substitution failed:". Here are some of the complaints: D:\Boost_1_60_0/boost/test/tools/detail/print_helper.hpp:50:14: note: cannot convert 't' (type 'const DiGSE::Operand_Class_Test_Suite::Operand_Default_Constructor_Test::test_method()::UsedFor') to type 'std::_Setw' ostr << t; ^ D:/Program Files/mingw-w64/x86_64-5.3.0-posix-seh-rt_v4-rev0/mingw64/x86_64-w64-mingw32/include/c++/iomanip:208:5: note: candidate: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, std::_Setprecision) operator<<(basic_ostream<_CharT, _Traits>& __os, _Setprecision __f) D:\Boost_1_60_0/boost/test/tools/detail/print_helper.hpp:50:14: note: cannot convert 't' (type 'const DiGSE::Operand_Class_Test_Suite::Operand_Default_Constructor_Test::test_method()::UsedFor') to type 'std::_Setprecision' ostr << t; ^ At this point, it seems to be complaining about every io manipulator in existence. D:\Boost_1_60_0/boost/test/tools/detail/print_helper.hpp:50:14: note: mismatched types 'const std::piecewise_linear_distribution<_RealType>' and 'const DiGSE::Operand_Class_Test_Suite::Operand_Default_Constructor_Test::test_method()::UsedFor' ostr << t; Then it gets to the point of, apparently, dragging out all of the error messages it doesn't get to use very often: mismatched types*'const std::chi_squared_distribution<_RealType>' *and 'const DiGSE::Operand_Class_Test_Suite::Operand_Default_Constructor_Test::test_method()::UsedFor' ostr << t; ^ For the time being, I can simply use the explicit == check, but it looks like there's a problem here. Merrill Cornish

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[ANN] build2 - C++ build toolchain
by Boris Kolpackov 03 Feb '16

03 Feb '16

Hi, build2 is an open source, cross-platform toolchain for building and packaging C++ code. It includes a build system, package manager, and repository web interface. We've also started cppget.org, a public repository of open source C++ packages. This is the first alpha release and currently it is more of a technology preview rather than anything that is ready for production. We have tested this version on various Linux'es, Mac OS, and FreeBSD. There is no Windows support yet (but cross-compilation is supported). The project's page is: https://build2.org For those who need to see examples right away, here is the introduction: https://build2.org/build2-toolchain/doc/build2-toolchain-intro.xhtml Enjoy, Boris

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BOOST_LOG_TRIVIAL destination change
by Marc Paschover 02 Feb '16

02 Feb '16

I am working on a native Excel add-in (using XLW+), and I have been using Boost.Logging to output some diagnostic information, using BOOST_LOG_TRIVIAL. I would like to see this information in the Output window of Visual Studio. It seems like I somehow need to change the destination to boost::logging::destination::dbg_window, but I haven't been able to figure out a way to do this globally. Is there a way to do this? Thanks, Marc.

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