[PATCH] libstdc++: Correct export checks for _GLIBCXX_EXTERN_TEMPLATE

[Tomasz Kaminski]

On Wed, Jun 24, 2026 at 1:11 PM Jonathan Wakely <jwakely@redhat.com> wrote:

> On Tue, 23 Jun 2026 at 18:52, Tomasz Kamiński <tkaminsk@redhat.com> wrote:
> >
> > Replace a basic_string specific _GLIBCXX_EXTERN_TEMPLATE > 0 with
> > simple check for _GLIBCXX_EXTERN_TEMPLATE. This make sure that
> > extern definition is also use for -O0 (default).
> > Exported declarations are also important for future extensibility,
> > as they always pick latest implementation.
> >
> > libstdc++-v3/ChangeLog:
> >
> >         * include/std/format (__do_vformat_to): Change the preprocessor
> >         check for __do_vformat_to.
> > ---
> > I haven't noticed the issue, because I was testing the build times
> > with -O2.
> >
> > Testing on x86_64-linux. OK for trunk and 16 when all test passes?
>
> OK for both
>
This is now also backported to GCC-16.

>
>
> >
> >  libstdc++-v3/include/std/format | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/libstdc++-v3/include/std/format
> b/libstdc++-v3/include/std/format
> > index 4a517b70889..db226ecb0c8 100644
> > --- a/libstdc++-v3/include/std/format
> > +++ b/libstdc++-v3/include/std/format
> > @@ -5381,7 +5381,7 @@ namespace __format
> >  // instantiates formatters for types stored in basic_format_arg, we can
> >  // support only single encoding, in this case unicode. This should cover
> >  // most common use cases.
> > -#if __cplusplus <= 202002L && _GLIBCXX_EXTERN_TEMPLATE > 0
> > +#if __cplusplus <= 202002L && _GLIBCXX_EXTERN_TEMPLATE
> >      extern template _Sink_iter<char>
> >        __do_vformat_to<char, 1>(_Sink_iter<char>, string_view,
> >                                format_context&);
> > --
> > 2.54.0
> >
>
>
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