https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107760
--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:fe54b57728c09ab0389e2bb3f079d5210566199d commit r14-6569-gfe54b57728c09ab0389e2bb3f079d5210566199d Author: Jonathan Wakely <jwak...@redhat.com> Date: Thu Dec 14 23:23:34 2023 +0000 libstdc++: Implement C++23 <print> header [PR107760] This adds the C++23 std::print functions, which use std::format to write to a FILE stream or std::ostream (defaulting to stdout). The new extern symbols are in the libstdc++exp.a archive, so we aren't committing to stable symbols in the DSO yet. There's a UTF-8 validating and transcoding function added by this change. That can certainly be optimized, but it's internal to libstdc++exp.a so can be tweaked later at leisure. Currently the external symbols work for all targets, but are only actually used for Windows, where it's necessary to transcode to UTF-16 to write to the console. The standard seems to encourage us to also diagnose invalid UTF-8 for non-Windows targets when writing to a terminal (and only when writing to a terminal), but I'm reliably informed that that wasn't the intent of the wording. Checking for invalid UTF-8 sequences only needs to happen for Windows, which is good as checking for a terminal requires a call to isatty, and on Linux that uses an ioctl syscall, which would make std::print ten times slower! Testing the std::print behaviour is difficult if it depends on whether the output stream is connected to a Windows console or not, as we can't (as far as I know) do that non-interactively in DejaGNU. One of the new tests uses the internal __write_to_terminal function directly. That allows us to verify its UTF-8 error handling on POSIX targets, even though that's not actually used by std::print. For Windows, that __write_to_terminal function transcodes to UTF-16 but then uses WriteConsoleW which fails unless it really is writing to the console. That means the 27_io/print/2.cc test FAILs on Windows. The UTF-16 transcoding has been manually tested using mingw-w64 and Wine, and appears to work. libstdc++-v3/ChangeLog: PR libstdc++/107760 * include/Makefile.am: Add new header. * include/Makefile.in: Regenerate. * include/bits/version.def (__cpp_lib_print): Define. * include/bits/version.h: Regenerate. * include/std/format (__literal_encoding_is_utf8): New function. (_Seq_sink::view()): New member function. * include/std/ostream (vprintf_nonunicode, vprintf_unicode) (print, println): New functions. * include/std/print: New file. * src/c++23/Makefile.am: Add new source file. * src/c++23/Makefile.in: Regenerate. * src/c++23/print.cc: New file. * testsuite/27_io/basic_ostream/print/1.cc: New test. * testsuite/27_io/print/1.cc: New test. * testsuite/27_io/print/2.cc: New test.
