Re: git: 6527682ab705 - main - src: Use gnu++17 as the default C++ standard
Date: Tue, 22 Apr 2025 18:40:25 UTC
On 4/11/25 13:14, Mark Millard wrote: > John Baldwin <jhb_at_FreeBSD.org> wrote on > Date: Fri, 11 Apr 2025 13:54:30 UTC : > >> The branch main has been updated by jhb: >> >> URL: https://cgit.FreeBSD.org/src/commit/?id=6527682ab7058e5023a2a6dea01d51c15dca701f >> >> commit 6527682ab7058e5023a2a6dea01d51c15dca701f >> Author: John Baldwin <jhb@FreeBSD.org> >> AuthorDate: 2025-04-11 13:53:50 +0000 >> Commit: John Baldwin <jhb@FreeBSD.org> >> CommitDate: 2025-04-11 13:53:50 +0000 >> >> src: Use gnu++17 as the default C++ standard >> >> Previously the compiler's default C++ standard was used unlike C where >> bsd.sys.mk explicitly sets a default language version. Setting an >> explicit default version will give a more uniform experience across >> different compilers and compiler versions. >> >> gnu++17 was chosen to match the default C standard. It is well >> supported by a wide range of clang (5+) and GCC (9+) versions. >> >> gnu++17 is also the default C++ standard in recent versions of clang >> (16+) and GCC (11+). As a result, many of the explicit CXXSTD >> settings in Makefiles had the effect of lowering the C++ standard >> instead of raising it as was originally intended and are removed. >> >> Note that the remaining explicit CXXSTD settings for atf and liblutok >> explicitly lower the standard to C++11 due to use of the deprecated >> auto_ptr<> template which is removed in later versions. >> >> Reviewed by: imp, asomers, dim, emaste >> Differential Revision: https://reviews.freebsd.org/D49223 > > [The note below is just a thought prompted by this. It applies > to the prior context as well.] > > As I understand many C++ ports use the system c++ toolchain > and libc++ to build and operate --and there is only one libc++ > available in some respects. If that is the case > . . . > > This ends ends up controlling the C++ library's features for > any libc++ library material used via any of: No, it does not. libc++ is mostly templates and uses many #ifdef's to provide support for multiple language standards. For the actual symbols required at runtime, we build libc++ such that it includes all of them (in particular, we use a higher CXXSTD to build libc++ itself and have for a long time). So, no, this doesn't change anything in libc++ itself. It merely changes the default C++ environment when using bsd.*.mk. The same is true of libstdc++ use by GCC. It also supports the full range of C++ versions in the dynamic library and does not require separate builds for different C++ versions. -- John Baldwin