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Subject: [Bug libstdc++/115099] compilation error: format thread::id
Date: Wed, 22 May 2024 09:05:13 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D115099

--- Comment #2 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:

https://gcc.gnu.org/g:1a5e4dd83788ea4c049d354d83ad58a6a3d747e6

commit r15-770-g1a5e4dd83788ea4c049d354d83ad58a6a3d747e6
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri May 17 10:55:32 2024 +0100

    libstdc++: Implement std::formatter<std::thread::id> without <sstream>
[PR115099]

    The std::thread::id formatter uses std::basic_ostringstream without
    including <sstream>, which went unnoticed because the test for it uses
    a stringstream to check the output is correct.

    The fix implemented here is to stop using basic_ostringstream for
    formatting thread::id and just use std::format instead.

    As a drive-by fix, the formatter specialization is constrained to
    require that the thread::id::native_handle_type can be formatted, to
    avoid making the formatter ill-formed if the pthread_t type is not a
    pointer or integer. Since non-void pointers can't be formatted, ensure
    that we convert pointers to const void* for formatting. Make a similar
    change to the existing operator<< overload so that in the unlikely case
    that pthread_t is a typedef for char* we don't treat it as a
    null-terminated string when inserting into a stream.

    libstdc++-v3/ChangeLog:

            PR libstdc++/115099
            * include/bits/std_thread.h: Declare formatter as friend of
            thread::id.
            * include/std/thread (operator<<): Convert non-void pointers to
            void pointers for output.
            (formatter): Add constraint that thread::native_handle_type is a
            pointer or integer.
            (formatter::format): Reimplement without basic_ostringstream.
            * testsuite/30_threads/thread/id/output.cc: Check output
            compiles before <sstream> has been included.=