On Tue, Apr 8, 2025 at 1:25 AM Jonathan Wakely <jwak...@redhat.com> wrote:
> When formatting floating-point values to wide strings there's a case
> where we invalidate a std::wstring buffer while a std::wstring_view is
> still referring to it.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/119671
> * include/std/format (__formatter_fp::format): Do not invalidate
> __wstr unless _M_localized returns a valid string.
> * testsuite/std/format/functions/format.cc: Check wide string
> formatting of floating-point types with classic locale.
> ---
>
> Tested x86_64-linux.
>
LGTM.
>
> libstdc++-v3/include/std/format | 6 +++---
> .../testsuite/std/format/functions/format.cc | 12 ++++++++++++
> 2 files changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/format
> b/libstdc++-v3/include/std/format
> index 01a53143d1c..2e9319cdda6 100644
> --- a/libstdc++-v3/include/std/format
> +++ b/libstdc++-v3/include/std/format
> @@ -1838,9 +1838,9 @@ namespace __format
>
> if (_M_spec._M_localized && __builtin_isfinite(__v))
> {
> - __wstr = _M_localize(__str, __expc, __fc.locale());
> - if (!__wstr.empty())
> - __str = __wstr;
> + auto __s = _M_localize(__str, __expc, __fc.locale());
> + if (!__s.empty())
> + __str = __wstr = std::move(__s);
> }
>
> size_t __width = _M_spec._M_get_width(__fc);
> diff --git a/libstdc++-v3/testsuite/std/format/functions/format.cc
> b/libstdc++-v3/testsuite/std/format/functions/format.cc
> index 000f2671816..93c33b456e6 100644
> --- a/libstdc++-v3/testsuite/std/format/functions/format.cc
> +++ b/libstdc++-v3/testsuite/std/format/functions/format.cc
> @@ -370,6 +370,18 @@ test_wchar()
> // P2909R4 Fix formatting of code units as integers (Dude, where’s my
> char?)
> s = std::format(L"{:d} {:d}", wchar_t(-1), char(-1));
> VERIFY( s.find('-') == std::wstring::npos );
> +
> + auto ws = std::format(L"{:L}", 0.5);
> + VERIFY( ws == L"0.5" );
> + // The default C locale.
> + std::locale cloc = std::locale::classic();
> + // PR libstdc++/119671 use-after-free formatting floating-point to
> wstring
> + ws = std::format(cloc, L"{:L}", 0.5);
> + VERIFY( ws == L"0.5" );
> + // A locale with no name, but with the same facets as the C locale.
> + std::locale locx(cloc, &std::use_facet<std::ctype<char>>(cloc));
> + ws = std::format(locx, L"{:L}", 0.5);
> + VERIFY( ws == L"0.5" );
> }
>
> void
> --
> 2.49.0
>
>
