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author | Jonathan Wakely <jwakely@redhat.com> | 2024-01-21 18:16:14 +0000 |
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committer | Jonathan Wakely <jwakely@redhat.com> | 2024-01-21 22:15:06 +0000 |
commit | 7431fcea6b72beb54abb1932c254ac0e76bd0bde (patch) | |
tree | 8225909fd4326ec917fb9c71c95720a7f7d7c507 /install-sh | |
parent | fba15da8fa518bfb8d3e061795bc3ca2dea01d27 (diff) | |
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libstdc++: Fix std::format for floating-point chrono::time_point [PR113500]
Currently trying to use std::format with certain specializations of
std::chrono::time_point is ill-formed, due to one member function of the
__formatter_chrono type which tries to write a time_point to an ostream.
For sys_time<floating-point> or sys_time with a period greater than days
there is no operator<< that can be used.
That operator<< is only needed when using an empty chrono-specs in the
format string, like "{}", but the ill-formed expression gives an error
even if not actually used. This means it's not possible to format some
other specializations of chrono::time_point, even when using a non-empty
chrono-specs.
This fixes it by avoiding using 'os << t' for all chrono::time_point
specializations, and instead using std::format("{:L%F %T}", t). So that
we continue to reject std::format("{}", sys_time{1.0s}) a check for
empty chrono-specs is added to the formatter<sys_time<D>, C>
specialization.
While testing this I noticed that the output for %S with a
floating-point duration was incorrect, as the subseconds part was being
appended to the seconds without a decimal point, and without the correct
number of leading zeros.
libstdc++-v3/ChangeLog:
PR libstdc++/113500
* include/bits/chrono_io.h (__formatter_chrono::_M_S): Fix
printing of subseconds with floating-point rep.
(__formatter_chrono::_M_format_to_ostream): Do not write
time_point specializations directly to the ostream.
(formatter<chrono::sys_time<D>, C>::parse): Do not allow an
empty chrono-spec if the type fails to meet the constraints for
writing to an ostream with operator<<.
* testsuite/std/time/clock/file/io.cc: Check formatting
non-integral times with empty chrono-specs.
* testsuite/std/time/clock/gps/io.cc: Likewise.
* testsuite/std/time/clock/utc/io.cc: Likewise.
* testsuite/std/time/hh_mm_ss/io.cc: Likewise.
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