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[Process] Help needed with boost::process::extend::on_*
by Günter Berner 26 Apr '18

26 Apr '18

I am using boost::process::child to create a child process: boost::process::child child("foo"); This works fine so far (on Linux + Windows). Now i want to use a handler which is executed during the fork process: boost::process::child child("foo", boost::process::extend::on_setup = [](auto& exec) { // ... }); This also works fine - as long as a more or less up-to-date C++ compiler or C++ standard. Since g++-4.8.5 (which I have to use) does not support auto template deduction for lambdas, i have to replace the lambda parameter type with a concrete type. boost::process::child child("foo", boost::process::extend::on_setup = [](<WHAT_GOES_HERE?>& exec) { // ... }); Boost.Process documentation only uses the modern approach with auto template deduction. I simply cannot find an example/documentation where the concrete types are shown. Thanks.

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failed coversion
by Markel, Joseph 25 Apr '18

25 Apr '18

Is there a way to get the int value by performing division on boost::any variables? #include <boost/any.hpp> int main(void) { boost::any a = 10; std::cout << boost::any_cast<int>(a) << std::endl; boost::any s = 2.5; // scaling factor // scale the value a = boost::any_cast<int>(a)/boost::any_cast<float>(s); std::cout << boost::any_cast<int>(a) << std::endl; } This throws the error boost::bad_any_cast: failed conversion using boost::any_cast Thanks CONFIDENTIALITY NOTICE: This e-mail communication and any attachments may contain proprietary and privileged information for the use of the designated recipients named above. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message.

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[multiprecision] static_cast<cpp_bin_float_100> gives strange values.
by Vögl, Christian 20 Apr '18

20 Apr '18

Hi everyone. The following Situation: I tried to improve the accuracy of a numerical function by replacing all double variables with cpp_bin_float_100. The parameters of this function contain two 3-element double arrays, which I convert to cpp_bin_float_100 by the following function: static void equal(cpp_bin_float_100* a, double* b) { for(int i=0; i<3;i++) { a[i]=static_cast<cpp_bin_float_100>(b[i]); } } the third element seems to be converted correctly, the first and second are totally off. (e. g. 100 -> 1.5625)

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[asio] Using struct ip_mreqn to joing multicast group
by Klebsch, Mario 20 Apr '18

20 Apr '18

Hi, I need to receive multicasts on multiple interfaces and handle them differently, depending on the network interface they arrived on. For each network interface, I create an UDP socket and I use Socket.set_option(boost::asio::ip::multicast::join_group(MCastReqAddr.to_v4(), LocalAddr.to_v4() ), ec); to join the multicast group. LocalAddr is the local IPv4 address of the interface. Unfortunately, I receive each incoming multicast message on each socket. I found, that boost::asio::ip::multicast::join_group uses struct ip_mreq, where the multicast address and the local address can be specified. On linux the man page on IP_ADD_MEMBERSHIP tells to use struct ip_mreqn. This structure had an additional member imr_ifindex. The documentation is not very clear about the difference between imr_address and imr_ifindex. So, I want to try it out and wonder, whether boost::asio supports using struct ip_mreqn for IP_ADD_MEMBERSHIP. If not, does anybody know, how to write my own class to be used with Socket.set_option? 73, Mario -- Mario Klebsch Actia I+ME GmbH Mario.klebsch(a)ime-actia.de<mailto:Mario.klebsch@ime-actia.de> Dresdenstrasse 17/18 Fon: +49 531 38 701 716 38124 Braunschweig Fax: +49 531 38 701 88 Germany

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Boost.Range and initializer_list
by Robert Jones 18 Apr '18

18 Apr '18

Hi All Does the Boost.Range library support initializer_list as a range type? I thought anything with begin() and end() methods was fair game, but this code doesn't work, unless I'm doing it wrong. #include <iostream> #include <vector> #include <boost/range/adaptor/reversed.hpp> int main( ) { using namespace std; using namespace boost::adaptors; vector<int> v { 1, 2, 3 }; for( int i : v | reversed ) { cout << i << " "; } // Ok for( int i : { 1, 2, 3 } | reversed ) { cout << i << " "; } // Bad } Kind Regards Rob.

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[Boost.Range] combine, native range-for, and destructuring
by John M. Dlugosz 18 Apr '18

18 Apr '18

I want to go through two vectors at the same time, and the way to do this is to "zip" the items from each into a tuple. boost::combine is a function for that. for (auto&[def,residue] : boost::combine(playdef, residues)) { gives me an error 1>e:\scratch\c++code\scratchproject2\fizzbuzz\fizzbuzz.cpp(66): error C2440: 'initializing': cannot convert from 'boost::tuples::cons<std::pair<int,std::string_view> &,boost::tuples::cons<int &,boost::fusion::detail::build_tuple_cons<boost::fusion::single_view_iterator<Sequence,boost::mpl::int_<1>>,Last,true>::type>>' to 'boost::tuples::cons<std::pair<int,std::string_view> &,boost::tuples::cons<int &,boost::fusion::detail::build_tuple_cons<boost::fusion::single_view_iterator<Sequence,boost::mpl::int_<1>>,Last,true>::type>> &' The only difference is in the final `&` character. Trying to explore the behavior in pieces, I try: for (auto row : boost::combine(playdef, residues)) { auto&[def, residue] = row; // line 1 row.get<1>() = 17; // line 2 residue= 42; // line 3 Now line2 does work, and I note that assignment goes through and updates the original `residues` vector. The destructuring on line 1 does compile now, being on a separate line. But line 3 gives me an error about not being able to assign to a crazy complicated type. What's going on? Is Boost.Range zipped ranges simply not compatible with the native language features?

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Turning off BOOST_IOSTREAMS_HAS_DINKUMWARE_FPOS for MSVC++
by Billy O'Neal (VC LIBS) 17 Apr '18

17 Apr '18

Hi folks! As part of a recent cleanup of some of our iostreams bits I removed a double-seek inside std::filebuf. (Previously, std::filebuf didn't take advantage that we know ::fsetpos just accepts a 64 bit number position) Moreover, in previous releases of MSVC++, that still would have been correct; filebuf was getting to the same place in a very indirect way. I know just casting std::fpos to a streamoff works to get the position going back to at least VS 2015, and it probably works a decade earlier than that (though I have not tested). Shame on us for adding a pretty name to std::fpos not depicted in the standard. Would you accept a patch to $\boost\iostreams\detail\config\fpos.hpp adding this guard before attempting to define BOOST_IOSTREAMS_HAS_DINKUMWARE_FPOS? !(_MSVC_STL_VERSION >= 141) I submitted a patch to do that here: https://github.com/boostorg/iostreams/pull/57 Thanks folks! Billy O'Neal Visual C++ Libraries

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Boost.Range and result_type
by Robert Jones 17 Apr '18

17 Apr '18

Hi All I have a suspicion this is all ancient history now, but I was surprised this code worked. #include <iostream> #include <vector> #include <boost/range/adaptor/transformed.hpp> struct TimesTwo { // using result_type = int; int operator( )( int i ) const { return i * 2; } }; int main( ) { using namespace std; using namespace boost::adaptors; vector<int> v { 0, 1, 2, 3, 4, 5 }; for( int i : v | transformed( TimesTwo( ) ) ) { cout << i << " "; } cout << endl; } Due to result_type being commented out. Am I right in thinking this is what BOOST_RESULT_OF_USE_DECLTYPE was all about, and everything now just works because modern compilers are implemtenting decltype now? Kind Regards Rob.

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[DateTime] localtime_r() issue
by Latimerius 16 Apr '18

16 Apr '18

Hi, I'm trying to build a project that uses Boost.Log (which in turn uses Date_Time) from Boost 1.65.1 on a platform that uses Clang with (apparently) Dinkumware for a standard library implementation. Compilation fails in date_time/c_time.hpp on line 67 due to a use of undeclared identifier 'localtime_r'. The standard library implementation indeed doesn't seem to have localtime_r(), just localtime_s(). Compilation of the failing code in c_time.hpp is enabled by the preprocessor symbol BOOST_DATE_TIME_HAS_REENTRANT_STD_FUNCTIONS having been #define'd which happens in date_time/compiler_config.hpp based on BOOST_HAS_THREADS being #define'd and a bunch of compiler checks that probably don't get it quite right. Could someone give me some advice how to deal with this? Thanks in advance!

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[release] Boost 1.67.0
by Daniel James 15 Apr '18

15 Apr '18

Release 1.67.0 of the Boost C++ Libraries is now available. These open-source libraries work well with the C++ Standard Library, and are usable across a broad spectrum of applications. The Boost license encourages both commercial and non-commercial use. This release contains 2 new libraries and numerous enhancements and bug fixes for existing libraries. For details, including download links, see <https://www.boost.org/users/news/version_1.67.0> You can also download directly from: <https://dl.bintray.com/boostorg/release/1.67.0/> To install this release on your system, see <https://www.boost.org/doc/libs/release/more/getting_started/index.html> Thanks to everyone who participated in this release. Thanks, -- The Boost Release Team

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