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libstdc++: Fix std::format thousands separators when sign present [PR120548] 

The leading sign character should be skipped when deciding whether to
insert thousands separators into a floating-point format.

libstdc++-v3/ChangeLog:

	PR libstdc++/120548
	* include/std/format (__formatter_fp::_M_localize): Do not
	include a leading sign character in the string to be grouped.
	* testsuite/std/format/functions/format.cc: Check grouping when
	sign is present in the output.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
(cherry picked from commit 2c3559839d)
This commit is contained in:
Jonathan Wakely 2025-06-04 18:22:28 +01:00 committed by Jonathan Wakely
parent 4f3ce8d046
commit f8ae6193b7
No known key found for this signature in database
2 changed files with 19 additions and 2 deletions
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11
libstdc++-v3/include/std/format
View File

@ -1745,9 +1745,16 @@ namespace __format
const size_t __r = __str.size() - __e; // Length of remainder.
auto __overwrite = [&](_CharT* __p, size_t) {
// Apply grouping to the digits before the radix or exponent.
auto __end = std::__add_grouping(__p, __np.thousands_sep(),
int __off = 0;
if (auto __c = __str.front(); __c == '-' || __c == '+' || __c == ' ')
{
*__p = __c;
__off = 1;
}
auto __end = std::__add_grouping(__p + __off, __np.thousands_sep(),
__grp.data(), __grp.size(),
__str.data(), __str.data() + __e);
__str.data() + __off,
__str.data() + __e);
if (__r) // If there's a fractional part or exponent
{
if (__d != __str.npos)

10
libstdc++-v3/testsuite/std/format/functions/format.cc
View File

@ -239,6 +239,16 @@ test_locale()
s = std::format(eloc, "{0:Le} {0:Lf} {0:Lg}", -nan);
VERIFY( s == "-nan -nan -nan" );
// PR libstdc++/120548 format confuses a negative sign for a thousands digit
s = std::format(bloc, "{:L}", -123.45);
VERIFY( s == "-123.45" );
s = std::format(bloc, "{:-L}", -876543.21);
VERIFY( s == "-876,543.21" );
s = std::format(bloc, "{:+L}", 333.22);
VERIFY( s == "+333.22" );
s = std::format(bloc, "{: L}", 999.44);
VERIFY( s == " 999.44" );
// Restore
std::locale::global(cloc);
}