----- Original Message ----- From: "John Maddock" <boost.regex@virgin.net> To: <boost@lists.boost.org> Sent: Wednesday, September 22, 2010 10:06 AM Subject: Re: [boost] [config] check forstd::numeric_limits<T>::lowest()availability
I would like to use std::numeric_limits<T>::lowest() when the standard library provides it. As this is a specific function on C++0X, I was looking for a macro on Boost.Config that allows to use it conditionally, unfortunatelly I have not found any.
Because, no one has asked for it yet :-)
Do you have a patch?
I can add a macro # define BOOST_NO_LIMITS_LOWEST which must be defined except for the libraries providing this template<class T> class std::numeric_limits { public: static constexpr T lowest() throw(); }; Of course constexpr must be managed by the already existing macro BOOST_NO_CONSTEXPR. I have followed the "Adding New Defect Macros" and thisnk that I have reached to create the new macro stuff. See attached patches. I guess that this macro should be defined in all the config/stdlib files except when this is provided. I have changed only thre files as I can not test others. BTW, on cygwin gcc-4.3.4 I get the following error related to nl_types.h file. ...updating 4 targets... gcc.compile.c++ ../../../bin.v2/libs/config/test/config_test.test/gcc-4.3.4/debug/config_test.o In file included from /usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/ext/hash_set:64, from boost_has_hash.ipp:16, from config_test.cpp:652: /usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/backward/backward_warning.h:33:2: warning: #warning This file includes at least one deprecated or antiquated header which may be removed without further notice at a future date. Please use a non-deprecated interface with equivalent functionality instead. For a listing of replacement headers and interfaces, consult the file backward_warning.h. To disable this warning use -Wno-deprecated. In file included from config_test.cpp:682: boost_has_nl_types_h.ipp:12:22: error: nl_types.h: No such file or directory It is normal that the default cygwin installation miss this file?
What will be the right way to do that? Any chance <boost/limmits.hpp> manage with that?
No, boost/limits.hpp just provides a replacement when the std version isn't available, and we can't extend numeric_limits ourselves, so yes a config macro would be the way to go.
John.
Beside the macro, I was thinking in adding a specific boost::numeric_limits traits, including the missing features. // boost/numeric_limits.hpp namespace boost { namespace detail { template <class T, bool = is_arithmetic<T>::value> struct numeric_limits { static T lowest() throw() {return (std::numeric_limits<T>::min) ();} }; template <class T> struct numeric_limits<T,true> { static T lowest() throw() {return (std::numeric_limits<T>::min) ();} }; template <> struct numeric_limits<float,true> { static float lowest() throw() {return -(std::numeric_limits<float>::max) ();} }; template <> struct numeric_limits<double,true> { static double lowest() throw() {return -(std::numeric_limits<double>::max) ();} }; template <> struct numeric_limits<long double,true> { static long double lowest() throw() {return -(std::numeric_limits<long double>::max)();} }; } #if defined(BOOST_NO_LIMITS_LOWEST) template <class T> struct numeric_limits : detail::numeric_limits<typename remove_cv<T>::type> {}; #else template <class T> struct numeric_limits { static T lowest() throw() {return std::numeric_limits<T>::lowest();} }; #endif } Let me know if this could be useful for others and be included in Boost. If yes I could send you a patch with tests and documentation included. Best, Vicente