On Fri, May 22, 2026 at 1:37 AM Jonathan Wakely <[email protected]> wrote:
> The standard explicitly requires the <ios> header to include <iosfwd>,
> which has declarations of all the standard stream buffers and stream
> types. Because we include <ios> in <istream> and <ostream>, this means
> that <iosfwd> is included everywhere, and so every iostream header has a
> forward declaration of every iostream type. This means that for example,
> <fstream> has a declaration (but not the definition) of std::stringbuf.
>
> This leads to a poor user experience, because the compiler's fixit hints
> for undeclared types do not trigger of the type _has_ been declared,
> instead users get an error about using an incomplete type. See the
> example in PR 125371, where using std::istringstream after including
> <fstream> fails to suggest including <sstream>.
>
> If we stop including <ios> in <istream> and <ostream>, and instead
> include _most_ of the same things that <ios> provides, then we can avoid
> the unhelpful declarations of the entire family of iostream types in
> every header. Users who really do want a declaration of std::filebuf
> or std::istringstream (but don't want the full definition) can still
> explicitly include <iosfwd> to get those declarations. But they won't
> get them as a side effect of <fstream> etc.
>
> Various headers currently include <iosfwd> because they really do want
> the declaration of e.g. std::ostream of std::streambuf_iterator. We can
> split <iosfwd> into five smaller headers and then only include the relevant
> one where required, e.g. <fstream> only needs to include iosfwd_file.h
> and not iosfwd_string.h.
>
> We need to add an explicit include of <ios> in <iostream>. The standard
> requires it there, and after this change we no longer get it via
> <istream> and <ostream>.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/125371
> * config/io/basic_file_stdio.h: Include <bits/ios_base.h>
> instead of <ios>.
> * include/Makefile.am: Add new headers.
> * include/Makefile.in: Regenerate.
> * include/bits/fs_path.h: Include <bits/iosfwd.h> instead of
> <iosfwd>.
> * include/bits/locale_facets.h: Remove unused <iosfwd> and
> <streambuf> includes.
> * include/bits/localefwd.h: Include <bits/iosfwd.h> instead of
> <iosfwd>.
> * include/bits/ostream.h: Replace <ios> with its constituent
> parts, except for <iosfwd>.
> * include/bits/ostream_insert.h: Include <bits/iosfwd.h> instead
> of <iosfwd>.
> * include/bits/shared_ptr.h: Likewise.
> * include/bits/std_thread.h: Likewise.
> * include/bits/stream_iterator.h: Likewise.
> * include/std/fstream: Include <bits/iosfwd_file.h>.
> * include/std/iomanip: Include <bits/iosfwd.h> instead of
> <iosfwd>.
> * include/std/ios: Do not include <exception> or
> <bits/char_traits.h>.
> * include/std/iosfwd: Move declarations to new headers and
> include those new headers. Tweak Doxygen comment.
> * include/std/iostream: Include <ios>.
> * include/std/istream: Replace <ios> with its constituent
> parts, except for <iosfwd>.
> * include/std/random: Include <bits/iosfwd.h> instead of
> <iosfwd>.
> * include/std/spanstream: Include <bits/iosfwd_span.h>.
> * include/std/sstream: Include <bits/iosfwd_string.h>.
> * include/std/streambuf: Include <bits/iosfwd.h> instead of
> <iosfwd>.
> * include/std/string_view: Likewise.
> * include/std/syncstream: Include <bits/iosfwd_sync.h>.
> * include/std/system_error: Include <bits/iosfwd.h> instead of
> <iosfwd>.
> * include/bits/iosfwd.h: New file.
> * include/bits/iosfwd_file.h: New file.
> * include/bits/iosfwd_span.h: New file.
> * include/bits/iosfwd_string.h: New file.
> * include/bits/iosfwd_sync.h: New file.
> ---
>
> v2: Kept the doxygen comment in <iosfwd> as requested by Tomasz.
> Also used some backticks for markup in that doxygen comment.
>
> Tested x86_64-linux.
>
LGTM
>
> libstdc++-v3/config/io/basic_file_stdio.h | 2 +-
> libstdc++-v3/include/Makefile.am | 5 +
> libstdc++-v3/include/Makefile.in | 5 +
> libstdc++-v3/include/bits/fs_path.h | 2 +-
> libstdc++-v3/include/bits/iosfwd.h | 112 +++++++++++
> libstdc++-v3/include/bits/iosfwd_file.h | 91 +++++++++
> libstdc++-v3/include/bits/iosfwd_span.h | 78 ++++++++
> libstdc++-v3/include/bits/iosfwd_string.h | 101 ++++++++++
> libstdc++-v3/include/bits/iosfwd_sync.h | 72 +++++++
> libstdc++-v3/include/bits/locale_facets.h | 2 -
> libstdc++-v3/include/bits/localefwd.h | 2 +-
> libstdc++-v3/include/bits/ostream.h | 7 +-
> libstdc++-v3/include/bits/ostream_insert.h | 2 +-
> libstdc++-v3/include/bits/shared_ptr.h | 2 +-
> libstdc++-v3/include/bits/std_thread.h | 2 +-
> libstdc++-v3/include/bits/stream_iterator.h | 2 +-
> libstdc++-v3/include/std/fstream | 1 +
> libstdc++-v3/include/std/iomanip | 2 +-
> libstdc++-v3/include/std/ios | 2 -
> libstdc++-v3/include/std/iosfwd | 208 ++------------------
> libstdc++-v3/include/std/iostream | 2 +-
> libstdc++-v3/include/std/istream | 8 +-
> libstdc++-v3/include/std/random | 2 +-
> libstdc++-v3/include/std/spanstream | 1 +
> libstdc++-v3/include/std/sstream | 1 +
> libstdc++-v3/include/std/streambuf | 2 +-
> libstdc++-v3/include/std/string_view | 2 +-
> libstdc++-v3/include/std/syncstream | 1 +
> libstdc++-v3/include/std/system_error | 2 +-
> 29 files changed, 505 insertions(+), 216 deletions(-)
> create mode 100644 libstdc++-v3/include/bits/iosfwd.h
> create mode 100644 libstdc++-v3/include/bits/iosfwd_file.h
> create mode 100644 libstdc++-v3/include/bits/iosfwd_span.h
> create mode 100644 libstdc++-v3/include/bits/iosfwd_string.h
> create mode 100644 libstdc++-v3/include/bits/iosfwd_sync.h
>
> diff --git a/libstdc++-v3/config/io/basic_file_stdio.h
> b/libstdc++-v3/config/io/basic_file_stdio.h
> index a4fd25271c2d..5e06fd378eab 100644
> --- a/libstdc++-v3/config/io/basic_file_stdio.h
> +++ b/libstdc++-v3/config/io/basic_file_stdio.h
> @@ -39,7 +39,7 @@
> #include <bits/c++config.h>
> #include <bits/c++io.h> // for __c_lock and __c_file
> #include <bits/move.h> // for swap
> -#include <ios>
> +#include <bits/ios_base.h> // For ios_base declarations.
>
> namespace std _GLIBCXX_VISIBILITY(default)
> {
> diff --git a/libstdc++-v3/include/Makefile.am
> b/libstdc++-v3/include/Makefile.am
> index ec932181a966..f91a93ae4aa6 100644
> --- a/libstdc++-v3/include/Makefile.am
> +++ b/libstdc++-v3/include/Makefile.am
> @@ -140,6 +140,11 @@ bits_freestanding = \
> ${bits_srcdir}/functional_hash.h \
> ${bits_srcdir}/intcmp.h \
> ${bits_srcdir}/invoke.h \
> + ${bits_srcdir}/iosfwd.h \
> + ${bits_srcdir}/iosfwd_file.h \
> + ${bits_srcdir}/iosfwd_span.h \
> + ${bits_srcdir}/iosfwd_string.h \
> + ${bits_srcdir}/iosfwd_sync.h \
> ${bits_srcdir}/iterator_concepts.h \
> ${bits_srcdir}/new_except.h \
> ${bits_srcdir}/new_throw.h \
> diff --git a/libstdc++-v3/include/Makefile.in
> b/libstdc++-v3/include/Makefile.in
> index 00ae5209f604..611ef30c6cdb 100644
> --- a/libstdc++-v3/include/Makefile.in
> +++ b/libstdc++-v3/include/Makefile.in
> @@ -498,6 +498,11 @@ bits_freestanding = \
> ${bits_srcdir}/functional_hash.h \
> ${bits_srcdir}/intcmp.h \
> ${bits_srcdir}/invoke.h \
> + ${bits_srcdir}/iosfwd.h \
> + ${bits_srcdir}/iosfwd_file.h \
> + ${bits_srcdir}/iosfwd_span.h \
> + ${bits_srcdir}/iosfwd_string.h \
> + ${bits_srcdir}/iosfwd_sync.h \
> ${bits_srcdir}/iterator_concepts.h \
> ${bits_srcdir}/new_except.h \
> ${bits_srcdir}/new_throw.h \
> diff --git a/libstdc++-v3/include/bits/fs_path.h
> b/libstdc++-v3/include/bits/fs_path.h
> index f0c8c47f0aed..8d0078000294 100644
> --- a/libstdc++-v3/include/bits/fs_path.h
> +++ b/libstdc++-v3/include/bits/fs_path.h
> @@ -34,11 +34,11 @@
>
> #include <type_traits>
> #include <locale>
> -#include <iosfwd>
> #include <iomanip>
> #include <codecvt>
> #include <string_view>
> #include <system_error>
> +#include <bits/iosfwd.h>
> #include <bits/stl_algobase.h>
> #include <bits/stl_pair.h>
> #include <bits/locale_conv.h>
> diff --git a/libstdc++-v3/include/bits/iosfwd.h
> b/libstdc++-v3/include/bits/iosfwd.h
> new file mode 100644
> index 000000000000..525482770b28
> --- /dev/null
> +++ b/libstdc++-v3/include/bits/iosfwd.h
> @@ -0,0 +1,112 @@
> +// <iosfwd> Forward declarations -*- C++ -*-
> +
> +// Copyright (C) 1997-2026 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +
> +// Under Section 7 of GPL version 3, you are granted additional
> +// permissions described in the GCC Runtime Library Exception, version
> +// 3.1, as published by the Free Software Foundation.
> +
> +// You should have received a copy of the GNU General Public License and
> +// a copy of the GCC Runtime Library Exception along with this program;
> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
> +// <http://www.gnu.org/licenses/>.
> +
> +/** @file include/iosfwd
> + * This is an internal header file, included by other library headers.
> + * Do not attempt to use it directly. @headername{iosfwd}
> + */
> +
> +#ifndef _GLIBCXX_IOSFWD_H
> +#define _GLIBCXX_IOSFWD_H 1
> +
> +#ifdef _GLIBCXX_SYSHDR
> +#pragma GCC system_header
> +#endif
> +
> +#include <bits/requires_hosted.h> // iostreams
> +
> +#include <bits/c++config.h>
> +#include <bits/char_traits.h> // For char_traits, streamoff, streamsize,
> fpos
> +
> +namespace std _GLIBCXX_VISIBILITY(default)
> +{
> +_GLIBCXX_BEGIN_NAMESPACE_VERSION
> +
> + /**
> + * @addtogroup io
> + * @{
> + */
> + class ios_base;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class basic_ios;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class basic_streambuf;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class basic_istream;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class basic_ostream;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class basic_iostream;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class istreambuf_iterator;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class ostreambuf_iterator;
> +
> +
> + /// Base class for @c char streams.
> + typedef basic_ios<char> ios;
> +
> + /// Base class for @c char buffers.
> + typedef basic_streambuf<char> streambuf;
> +
> + /// Base class for @c char input streams.
> + typedef basic_istream<char> istream;
> +
> + /// Base class for @c char output streams.
> + typedef basic_ostream<char> ostream;
> +
> + /// Base class for @c char mixed input and output streams.
> + typedef basic_iostream<char> iostream;
> +
> +
> +#ifdef _GLIBCXX_USE_WCHAR_T
> + /// Base class for @c wchar_t streams.
> + typedef basic_ios<wchar_t> wios;
> +
> + /// Base class for @c wchar_t buffers.
> + typedef basic_streambuf<wchar_t> wstreambuf;
> +
> + /// Base class for @c wchar_t input streams.
> + typedef basic_istream<wchar_t> wistream;
> +
> + /// Base class for @c wchar_t output streams.
> + typedef basic_ostream<wchar_t> wostream;
> +
> + /// Base class for @c wchar_t mixed input and output streams.
> + typedef basic_iostream<wchar_t> wiostream;
> +#endif
> +
> + /** @} */
> +
> +_GLIBCXX_END_NAMESPACE_VERSION
> +} // namespace
> +
> +#endif /* _GLIBCXX_IOSFWD_H */
> diff --git a/libstdc++-v3/include/bits/iosfwd_file.h
> b/libstdc++-v3/include/bits/iosfwd_file.h
> new file mode 100644
> index 000000000000..dc7359de02f7
> --- /dev/null
> +++ b/libstdc++-v3/include/bits/iosfwd_file.h
> @@ -0,0 +1,91 @@
> +// <iosfwd> Forward declarations for <fstream> -*- C++ -*-
> +
> +// Copyright (C) 1997-2026 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +
> +// Under Section 7 of GPL version 3, you are granted additional
> +// permissions described in the GCC Runtime Library Exception, version
> +// 3.1, as published by the Free Software Foundation.
> +
> +// You should have received a copy of the GNU General Public License and
> +// a copy of the GCC Runtime Library Exception along with this program;
> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
> +// <http://www.gnu.org/licenses/>.
> +
> +/** @file include/bits/iosfwd_file.h
> + * This is an internal header file, included by other library headers.
> + * Do not attempt to use it directly. @headername{iosfwd}
> + */
> +
> +#ifndef _GLIBCXX_IOSFWD_FILE_H
> +#define _GLIBCXX_IOSFWD_FILE_H 1
> +
> +#ifdef _GLIBCXX_SYSHDR
> +#pragma GCC system_header
> +#endif
> +
> +#include <bits/requires_hosted.h> // iostreams
> +
> +#include <bits/iosfwd.h>
> +
> +namespace std _GLIBCXX_VISIBILITY(default)
> +{
> +_GLIBCXX_BEGIN_NAMESPACE_VERSION
> +
> + /**
> + * @addtogroup io
> + * @{
> + */
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class basic_filebuf;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class basic_ifstream;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class basic_ofstream;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT> >
> + class basic_fstream;
> +
> + /// Class for @c char file buffers.
> + typedef basic_filebuf<char> filebuf;
> +
> + /// Class for @c char input file streams.
> + typedef basic_ifstream<char> ifstream;
> +
> + /// Class for @c char output file streams.
> + typedef basic_ofstream<char> ofstream;
> +
> + /// Class for @c char mixed input and output file streams.
> + typedef basic_fstream<char> fstream;
> +
> +#ifdef _GLIBCXX_USE_WCHAR_T
> + /// Class for @c wchar_t file buffers.
> + typedef basic_filebuf<wchar_t> wfilebuf;
> +
> + /// Class for @c wchar_t input file streams.
> + typedef basic_ifstream<wchar_t> wifstream;
> +
> + /// Class for @c wchar_t output file streams.
> + typedef basic_ofstream<wchar_t> wofstream;
> +
> + /// Class for @c wchar_t mixed input and output file streams.
> + typedef basic_fstream<wchar_t> wfstream;
> +#endif
> + /// @}
> +
> +_GLIBCXX_END_NAMESPACE_VERSION
> +} // namespace
> +
> +#endif /* _GLIBCXX_IOSFWD_FILE_H */
> diff --git a/libstdc++-v3/include/bits/iosfwd_span.h
> b/libstdc++-v3/include/bits/iosfwd_span.h
> new file mode 100644
> index 000000000000..13d998d477e4
> --- /dev/null
> +++ b/libstdc++-v3/include/bits/iosfwd_span.h
> @@ -0,0 +1,78 @@
> +// <iosfwd> Forward declarations for <spanstream> -*- C++ -*-
> +
> +// Copyright (C) 2022-2026 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +
> +// Under Section 7 of GPL version 3, you are granted additional
> +// permissions described in the GCC Runtime Library Exception, version
> +// 3.1, as published by the Free Software Foundation.
> +
> +// You should have received a copy of the GNU General Public License and
> +// a copy of the GCC Runtime Library Exception along with this program;
> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
> +// <http://www.gnu.org/licenses/>.
> +
> +/** @file include/bits/iosfwd_span.h
> + * This is an internal header file, included by other library headers.
> + * Do not attempt to use it directly. @headername{iosfwd}
> + */
> +
> +#ifndef _GLIBCXX_IOSFWD_SPAN_H
> +#define _GLIBCXX_IOSFWD_SPAN_H 1
> +
> +#ifdef _GLIBCXX_SYSHDR
> +#pragma GCC system_header
> +#endif
> +
> +#include <bits/requires_hosted.h> // iostreams
> +
> +#include <bits/version.h>
> +
> +#ifdef __glibcxx_spanstream // >= C++23
> +#include <bits/iosfwd.h>
> +
> +namespace std _GLIBCXX_VISIBILITY(default)
> +{
> +_GLIBCXX_BEGIN_NAMESPACE_VERSION
> +
> + /**
> + * @addtogroup io
> + * @{
> + */
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT>>
> + class basic_spanbuf;
> + template<typename _CharT, typename _Traits = char_traits<_CharT>>
> + class basic_ispanstream;
> + template<typename _CharT, typename _Traits = char_traits<_CharT>>
> + class basic_ospanstream;
> + template<typename _CharT, typename _Traits = char_traits<_CharT>>
> + class basic_spanstream;
> +
> + using spanbuf = basic_spanbuf<char>;
> + using ispanstream = basic_ispanstream<char>;
> + using ospanstream = basic_ospanstream<char>;
> + using spanstream = basic_spanstream<char>;
> +
> +#ifdef _GLIBCXX_USE_WCHAR_T
> + using wspanbuf = basic_spanbuf<wchar_t>;
> + using wispanstream = basic_ispanstream<wchar_t>;
> + using wospanstream = basic_ospanstream<wchar_t>;
> + using wspanstream = basic_spanstream<wchar_t>;
> +#endif
> + /// @}
> +
> +_GLIBCXX_END_NAMESPACE_VERSION
> +} // namespace
> +#endif // C++23
> +#endif /* _GLIBCXX_IOSFWD_SPAN_H */
> diff --git a/libstdc++-v3/include/bits/iosfwd_string.h
> b/libstdc++-v3/include/bits/iosfwd_string.h
> new file mode 100644
> index 000000000000..28daa101d4ba
> --- /dev/null
> +++ b/libstdc++-v3/include/bits/iosfwd_string.h
> @@ -0,0 +1,101 @@
> +// <iosfwd> Forward declarations for <sstream> -*- C++ -*-
> +
> +// Copyright (C) 1997-2026 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +
> +// Under Section 7 of GPL version 3, you are granted additional
> +// permissions described in the GCC Runtime Library Exception, version
> +// 3.1, as published by the Free Software Foundation.
> +
> +// You should have received a copy of the GNU General Public License and
> +// a copy of the GCC Runtime Library Exception along with this program;
> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
> +// <http://www.gnu.org/licenses/>.
> +
> +/** @file include/bits/iosfwd_string.h
> + * This is an internal header file, included by other library headers.
> + * Do not attempt to use it directly. @headername{iosfwd}
> + */
> +
> +#ifndef _GLIBCXX_IOSFWD_STRING_H
> +#define _GLIBCXX_IOSFWD_STRING_H 1
> +
> +#ifdef _GLIBCXX_SYSHDR
> +#pragma GCC system_header
> +#endif
> +
> +#include <bits/requires_hosted.h> // iostreams
> +
> +#include <bits/iosfwd.h>
> +#include <bits/stringfwd.h> // For string forward declarations.
> +
> +namespace std _GLIBCXX_VISIBILITY(default)
> +{
> +_GLIBCXX_BEGIN_NAMESPACE_VERSION
> +
> + /**
> + * @addtogroup io
> + * @{
> + */
> +
> +_GLIBCXX_BEGIN_NAMESPACE_CXX11
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT>,
> + typename _Alloc = allocator<_CharT> >
> + class basic_stringbuf;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT>,
> + typename _Alloc = allocator<_CharT> >
> + class basic_istringstream;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT>,
> + typename _Alloc = allocator<_CharT> >
> + class basic_ostringstream;
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT>,
> + typename _Alloc = allocator<_CharT> >
> + class basic_stringstream;
> +
> +_GLIBCXX_END_NAMESPACE_CXX11
> +
> + /// Class for @c char memory buffers.
> + typedef basic_stringbuf<char> stringbuf;
> +
> + /// Class for @c char input memory streams.
> + typedef basic_istringstream<char> istringstream;
> +
> + /// Class for @c char output memory streams.
> + typedef basic_ostringstream<char> ostringstream;
> +
> + /// Class for @c char mixed input and output memory streams.
> + typedef basic_stringstream<char> stringstream;
> +
> +#ifdef _GLIBCXX_USE_WCHAR_T
> + /// Class for @c wchar_t memory buffers.
> + typedef basic_stringbuf<wchar_t> wstringbuf;
> +
> + /// Class for @c wchar_t input memory streams.
> + typedef basic_istringstream<wchar_t> wistringstream;
> +
> + /// Class for @c wchar_t output memory streams.
> + typedef basic_ostringstream<wchar_t> wostringstream;
> +
> + /// Class for @c wchar_t mixed input and output memory streams.
> + typedef basic_stringstream<wchar_t> wstringstream;
> +#endif
> + /// @}
> +
> +_GLIBCXX_END_NAMESPACE_VERSION
> +} // namespace
> +
> +#endif /* _GLIBCXX_IOSFWD_STRING_H */
> diff --git a/libstdc++-v3/include/bits/iosfwd_sync.h
> b/libstdc++-v3/include/bits/iosfwd_sync.h
> new file mode 100644
> index 000000000000..9f5e9948e74a
> --- /dev/null
> +++ b/libstdc++-v3/include/bits/iosfwd_sync.h
> @@ -0,0 +1,72 @@
> +// <iosfwd> Forward declarations for <syncstream> -*- C++ -*-
> +
> +// Copyright (C) 2022-2026 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +
> +// Under Section 7 of GPL version 3, you are granted additional
> +// permissions described in the GCC Runtime Library Exception, version
> +// 3.1, as published by the Free Software Foundation.
> +
> +// You should have received a copy of the GNU General Public License and
> +// a copy of the GCC Runtime Library Exception along with this program;
> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
> +// <http://www.gnu.org/licenses/>.
> +
> +/** @file include/bits/iosfwd_sync.h
> + * This is an internal header file, included by other library headers.
> + * Do not attempt to use it directly. @headername{iosfwd}
> + */
> +
> +#ifndef _GLIBCXX_IOSFWD_SYNC_H
> +#define _GLIBCXX_IOSFWD_SYNC_H 1
> +
> +#ifdef _GLIBCXX_SYSHDR
> +#pragma GCC system_header
> +#endif
> +
> +#include <bits/requires_hosted.h> // iostreams
> +
> +#include <bits/version.h>
> +
> +#ifdef __glibcxx_syncbuf // >= C++20 && CXX11_ABI
> +#include <bits/iosfwd.h>
> +
> +namespace std _GLIBCXX_VISIBILITY(default)
> +{
> +_GLIBCXX_BEGIN_NAMESPACE_VERSION
> +
> + /**
> + * @addtogroup io
> + * @{
> + */
> +
> + template<typename _CharT, typename _Traits = char_traits<_CharT>,
> + typename _Allocator = allocator<_CharT>>
> + class basic_syncbuf;
> + template<typename _CharT, typename _Traits = char_traits<_CharT>,
> + typename _Allocator = allocator<_CharT>>
> + class basic_osyncstream;
> +
> + using syncbuf = basic_syncbuf<char>;
> + using osyncstream = basic_osyncstream<char>;
> +
> +#ifdef _GLIBCXX_USE_WCHAR_T
> + using wsyncbuf = basic_syncbuf<wchar_t>;
> + using wosyncstream = basic_osyncstream<wchar_t>;
> +#endif
> + /// @}
> +
> +_GLIBCXX_END_NAMESPACE_VERSION
> +} // namespace
> +#endif // __glibcxx_syncbuf
> +#endif /* _GLIBCXX_IOSFWD_SYNC_H */
> diff --git a/libstdc++-v3/include/bits/locale_facets.h
> b/libstdc++-v3/include/bits/locale_facets.h
> index ba6f6e694ff1..902ba047b265 100644
> --- a/libstdc++-v3/include/bits/locale_facets.h
> +++ b/libstdc++-v3/include/bits/locale_facets.h
> @@ -41,9 +41,7 @@
> #include <cwctype> // For wctype_t
> #include <cctype>
> #include <bits/ctype_base.h>
> -#include <iosfwd>
> #include <bits/ios_base.h> // For ios_base, ios_base::iostate
> -#include <streambuf>
> #include <bits/cpp_type_traits.h>
> #include <ext/type_traits.h>
> #include <ext/numeric_traits.h>
> diff --git a/libstdc++-v3/include/bits/localefwd.h
> b/libstdc++-v3/include/bits/localefwd.h
> index 4e4836d523cc..dcab8b331085 100644
> --- a/libstdc++-v3/include/bits/localefwd.h
> +++ b/libstdc++-v3/include/bits/localefwd.h
> @@ -40,7 +40,7 @@
>
> #include <bits/c++config.h>
> #include <bits/c++locale.h> // Defines __c_locale, config-specific
> include
> -#include <iosfwd> // For ostreambuf_iterator,
> istreambuf_iterator
> +#include <bits/iosfwd.h> // For ostreambuf_iterator,
> istreambuf_iterator
> #include <cctype>
>
> namespace std _GLIBCXX_VISIBILITY(default)
> diff --git a/libstdc++-v3/include/bits/ostream.h
> b/libstdc++-v3/include/bits/ostream.h
> index 7c53b21bdb3d..703ebf7890cd 100644
> --- a/libstdc++-v3/include/bits/ostream.h
> +++ b/libstdc++-v3/include/bits/ostream.h
> @@ -40,7 +40,12 @@
>
> #include <bits/requires_hosted.h> // iostreams
>
> -#include <ios>
> +#include <bits/iosfwd.h> // For declarations of default template
> args.
> +#include <bits/char_traits.h> // For char_traits, streamoff, streamsize,
> fpos
> +#include <bits/localefwd.h> // For class locale
> +#include <bits/ios_base.h> // For ios_base declarations.
> +#include <streambuf>
> +#include <bits/basic_ios.h>
> #include <bits/ostream_insert.h>
>
> # define __glibcxx_want_print
> diff --git a/libstdc++-v3/include/bits/ostream_insert.h
> b/libstdc++-v3/include/bits/ostream_insert.h
> index 4e52a1d164cb..a512283502ea 100644
> --- a/libstdc++-v3/include/bits/ostream_insert.h
> +++ b/libstdc++-v3/include/bits/ostream_insert.h
> @@ -34,7 +34,7 @@
> #pragma GCC system_header
> #endif
>
> -#include <iosfwd>
> +#include <bits/iosfwd.h>
> #include <bits/cxxabi_forced.h>
> #include <bits/exception_defines.h>
>
> diff --git a/libstdc++-v3/include/bits/shared_ptr.h
> b/libstdc++-v3/include/bits/shared_ptr.h
> index ada32d3d3cb9..8be9aace1711 100644
> --- a/libstdc++-v3/include/bits/shared_ptr.h
> +++ b/libstdc++-v3/include/bits/shared_ptr.h
> @@ -49,7 +49,7 @@
> #ifndef _SHARED_PTR_H
> #define _SHARED_PTR_H 1
>
> -#include <iosfwd> // std::basic_ostream
> +#include <bits/iosfwd.h> // std::basic_ostream
> #include <bits/shared_ptr_base.h>
>
> namespace std _GLIBCXX_VISIBILITY(default)
> diff --git a/libstdc++-v3/include/bits/std_thread.h
> b/libstdc++-v3/include/bits/std_thread.h
> index 9e85ae2c6e2e..7e529897998f 100644
> --- a/libstdc++-v3/include/bits/std_thread.h
> +++ b/libstdc++-v3/include/bits/std_thread.h
> @@ -37,7 +37,7 @@
> #if __cplusplus >= 201103L
> #include <bits/c++config.h>
>
> -#include <iosfwd> // std::basic_ostream
> +#include <bits/iosfwd.h> // std::basic_ostream
> #include <tuple> // std::tuple
> #include <bits/functional_hash.h> // std::hash
> #include <bits/invoke.h> // std::__invoke
> diff --git a/libstdc++-v3/include/bits/stream_iterator.h
> b/libstdc++-v3/include/bits/stream_iterator.h
> index 54130026ec29..74da499bc7dd 100644
> --- a/libstdc++-v3/include/bits/stream_iterator.h
> +++ b/libstdc++-v3/include/bits/stream_iterator.h
> @@ -34,7 +34,7 @@
> #pragma GCC system_header
> #endif
>
> -#include <iosfwd>
> +#include <bits/iosfwd.h>
> #include <bits/move.h>
> #include <bits/stl_iterator_base_types.h>
> #include <debug/debug.h>
> diff --git a/libstdc++-v3/include/std/fstream
> b/libstdc++-v3/include/std/fstream
> index c4e222b8fefb..653d417c6288 100644
> --- a/libstdc++-v3/include/std/fstream
> +++ b/libstdc++-v3/include/std/fstream
> @@ -41,6 +41,7 @@
>
> #include <istream>
> #include <ostream>
> +#include <bits/iosfwd_file.h>
> #include <bits/codecvt.h>
> #include <cstdio> // For BUFSIZ
> #include <bits/basic_file.h> // For __basic_file, __c_lock
> diff --git a/libstdc++-v3/include/std/iomanip
> b/libstdc++-v3/include/std/iomanip
> index 3841390b6335..34a9edf178c4 100644
> --- a/libstdc++-v3/include/std/iomanip
> +++ b/libstdc++-v3/include/std/iomanip
> @@ -43,7 +43,7 @@
> #include <bits/requires_hosted.h> // iostreams
>
> #include <bits/c++config.h>
> -#include <iosfwd>
> +#include <bits/iosfwd.h>
> #include <bits/ios_base.h>
>
> #define __glibcxx_want_quoted_string_io
> diff --git a/libstdc++-v3/include/std/ios b/libstdc++-v3/include/std/ios
> index 49f3aafd1de0..e9b1d6a165cd 100644
> --- a/libstdc++-v3/include/std/ios
> +++ b/libstdc++-v3/include/std/ios
> @@ -40,8 +40,6 @@
> #include <bits/requires_hosted.h> // iostreams
>
> #include <iosfwd>
> -#include <exception> // For ios_base::failure
> -#include <bits/char_traits.h> // For char_traits, streamoff, streamsize,
> fpos
> #include <bits/localefwd.h> // For class locale
> #include <bits/ios_base.h> // For ios_base declarations.
> #include <streambuf>
> diff --git a/libstdc++-v3/include/std/iosfwd
> b/libstdc++-v3/include/std/iosfwd
> index 42124ad30df4..1d5e684b53bb 100644
> --- a/libstdc++-v3/include/std/iosfwd
> +++ b/libstdc++-v3/include/std/iosfwd
> @@ -39,222 +39,36 @@
>
> #include <bits/requires_hosted.h> // iostreams
>
> -#include <bits/c++config.h>
> -#include <bits/stringfwd.h> // For string forward declarations.
> -#include <bits/postypes.h>
> -
> -namespace std _GLIBCXX_VISIBILITY(default)
> -{
> -_GLIBCXX_BEGIN_NAMESPACE_VERSION
> -
> /**
> * @defgroup io I/O
> *
> * Nearly all of the I/O classes are parameterized on the type of
> - * characters they read and write. (The major exception is ios_base at
> + * characters they read and write. (The major exception is `ios_base`
> at
> * the top of the hierarchy.) This is a change from pre-Standard
> * streams, which were not templates.
> *
> - * For ease of use and compatibility, all of the basic_* I/O-related
> + * For ease of use and compatibility, all of the `basic_*` I/O-related
> * classes are given typedef names for both of the builtin character
> * widths (wide and narrow). The typedefs are the same as the
> * pre-Standard names, for example:
> *
> - * @code
> + * ```
> * typedef basic_ifstream<char> ifstream;
> - * @endcode
> + * ```
> *
> * Because properly forward-declaring these classes can be difficult,
> you
> - * should not do it yourself. Instead, include the <iosfwd>
> + * should not do it yourself. Instead, include the `<iosfwd>`
> * header, which contains only declarations of all the I/O classes as
> * well as the typedefs. Trying to forward-declare the typedefs
> - * themselves (e.g., <code>class ostream;</code>) is not valid ISO C++.
> + * themselves (e.g., `class ostream;`) is not valid ISO C++.
> *
> * For more specific declarations, see
> *
> https://gcc.gnu.org/onlinedocs/libstdc++/manual/io.html#std.io.objects
> - *
> - * @{
> - */
> - class ios_base;
> + */
>
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class basic_ios;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class basic_streambuf;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class basic_istream;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class basic_ostream;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class basic_iostream;
> -
> -
> -_GLIBCXX_BEGIN_NAMESPACE_CXX11
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT>,
> - typename _Alloc = allocator<_CharT> >
> - class basic_stringbuf;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT>,
> - typename _Alloc = allocator<_CharT> >
> - class basic_istringstream;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT>,
> - typename _Alloc = allocator<_CharT> >
> - class basic_ostringstream;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT>,
> - typename _Alloc = allocator<_CharT> >
> - class basic_stringstream;
> -
> -_GLIBCXX_END_NAMESPACE_CXX11
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class basic_filebuf;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class basic_ifstream;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class basic_ofstream;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class basic_fstream;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class istreambuf_iterator;
> -
> - template<typename _CharT, typename _Traits = char_traits<_CharT> >
> - class ostreambuf_iterator;
> -
> -
> - /// Base class for @c char streams.
> - typedef basic_ios<char> ios;
> -
> - /// Base class for @c char buffers.
> - typedef basic_streambuf<char> streambuf;
> -
> - /// Base class for @c char input streams.
> - typedef basic_istream<char> istream;
> -
> - /// Base class for @c char output streams.
> - typedef basic_ostream<char> ostream;
> -
> - /// Base class for @c char mixed input and output streams.
> - typedef basic_iostream<char> iostream;
> -
> - /// Class for @c char memory buffers.
> - typedef basic_stringbuf<char> stringbuf;
> -
> - /// Class for @c char input memory streams.
> - typedef basic_istringstream<char> istringstream;
> -
> - /// Class for @c char output memory streams.
> - typedef basic_ostringstream<char> ostringstream;
> -
> - /// Class for @c char mixed input and output memory streams.
> - typedef basic_stringstream<char> stringstream;
> -
> - /// Class for @c char file buffers.
> - typedef basic_filebuf<char> filebuf;
> -
> - /// Class for @c char input file streams.
> - typedef basic_ifstream<char> ifstream;
> -
> - /// Class for @c char output file streams.
> - typedef basic_ofstream<char> ofstream;
> -
> - /// Class for @c char mixed input and output file streams.
> - typedef basic_fstream<char> fstream;
> -
> -#ifdef _GLIBCXX_USE_WCHAR_T
> - /// Base class for @c wchar_t streams.
> - typedef basic_ios<wchar_t> wios;
> -
> - /// Base class for @c wchar_t buffers.
> - typedef basic_streambuf<wchar_t> wstreambuf;
> -
> - /// Base class for @c wchar_t input streams.
> - typedef basic_istream<wchar_t> wistream;
> -
> - /// Base class for @c wchar_t output streams.
> - typedef basic_ostream<wchar_t> wostream;
> -
> - /// Base class for @c wchar_t mixed input and output streams.
> - typedef basic_iostream<wchar_t> wiostream;
> -
> - /// Class for @c wchar_t memory buffers.
> - typedef basic_stringbuf<wchar_t> wstringbuf;
> -
> - /// Class for @c wchar_t input memory streams.
> - typedef basic_istringstream<wchar_t> wistringstream;
> -
> - /// Class for @c wchar_t output memory streams.
> - typedef basic_ostringstream<wchar_t> wostringstream;
> -
> - /// Class for @c wchar_t mixed input and output memory streams.
> - typedef basic_stringstream<wchar_t> wstringstream;
> -
> - /// Class for @c wchar_t file buffers.
> - typedef basic_filebuf<wchar_t> wfilebuf;
> -
> - /// Class for @c wchar_t input file streams.
> - typedef basic_ifstream<wchar_t> wifstream;
> -
> - /// Class for @c wchar_t output file streams.
> - typedef basic_ofstream<wchar_t> wofstream;
> -
> - /// Class for @c wchar_t mixed input and output file streams.
> - typedef basic_fstream<wchar_t> wfstream;
> -#endif
> -
> -#if __cplusplus >= 202002L && _GLIBCXX_USE_CXX11_ABI
> - template<typename _CharT, typename _Traits = char_traits<_CharT>,
> - typename _Allocator = allocator<_CharT>>
> - class basic_syncbuf;
> - template<typename _CharT, typename _Traits = char_traits<_CharT>,
> - typename _Allocator = allocator<_CharT>>
> - class basic_osyncstream;
> -
> - using syncbuf = basic_syncbuf<char>;
> - using osyncstream = basic_osyncstream<char>;
> -
> -#ifdef _GLIBCXX_USE_WCHAR_T
> - using wsyncbuf = basic_syncbuf<wchar_t>;
> - using wosyncstream = basic_osyncstream<wchar_t>;
> -#endif
> -#endif // C++20 && CXX11_ABI
> -
> -#if __cplusplus > 202002L
> - template<typename _CharT, typename _Traits = char_traits<_CharT>>
> - class basic_spanbuf;
> - template<typename _CharT, typename _Traits = char_traits<_CharT>>
> - class basic_ispanstream;
> - template<typename _CharT, typename _Traits = char_traits<_CharT>>
> - class basic_ospanstream;
> - template<typename _CharT, typename _Traits = char_traits<_CharT>>
> - class basic_spanstream;
> -
> - using spanbuf = basic_spanbuf<char>;
> - using ispanstream = basic_ispanstream<char>;
> - using ospanstream = basic_ospanstream<char>;
> - using spanstream = basic_spanstream<char>;
> -
> -#ifdef _GLIBCXX_USE_WCHAR_T
> - using wspanbuf = basic_spanbuf<wchar_t>;
> - using wispanstream = basic_ispanstream<wchar_t>;
> - using wospanstream = basic_ospanstream<wchar_t>;
> - using wspanstream = basic_spanstream<wchar_t>;
> -#endif
> -#endif // C++23
> -
> - /** @} */
> -
> -_GLIBCXX_END_NAMESPACE_VERSION
> -} // namespace
> +#include <bits/iosfwd_file.h>
> +#include <bits/iosfwd_string.h>
> +#include <bits/iosfwd_sync.h>
> +#include <bits/iosfwd_span.h>
>
> #endif /* _GLIBCXX_IOSFWD */
> diff --git a/libstdc++-v3/include/std/iostream
> b/libstdc++-v3/include/std/iostream
> index f4b5fd868346..4b97dd2951ae 100644
> --- a/libstdc++-v3/include/std/iostream
> +++ b/libstdc++-v3/include/std/iostream
> @@ -39,7 +39,7 @@
>
> #include <bits/requires_hosted.h> // iostreams
>
> -#include <bits/c++config.h>
> +#include <ios>
> #include <ostream>
> #include <istream>
>
> diff --git a/libstdc++-v3/include/std/istream
> b/libstdc++-v3/include/std/istream
> index 6a982460a1dc..9b8474a0da8d 100644
> --- a/libstdc++-v3/include/std/istream
> +++ b/libstdc++-v3/include/std/istream
> @@ -39,7 +39,13 @@
>
> #include <bits/requires_hosted.h> // iostreams
>
> -#include <ios>
> +#include <bits/iosfwd.h> // For declarations of default template
> args.
> +#include <bits/char_traits.h> // For char_traits, streamoff, streamsize,
> fpos
> +#include <bits/localefwd.h> // For class locale
> +#include <bits/ios_base.h> // For ios_base declarations.
> +#include <streambuf>
> +#include <bits/basic_ios.h>
> +
> #include <ostream>
>
> #if __cplusplus > 202302L
> diff --git a/libstdc++-v3/include/std/random
> b/libstdc++-v3/include/std/random
> index ebbd9be296ea..ad512764a852 100644
> --- a/libstdc++-v3/include/std/random
> +++ b/libstdc++-v3/include/std/random
> @@ -46,7 +46,7 @@
> #include <cstdint> // For uint_fast32_t, uint_fast64_t, uint_least32_t
> #include <cstdlib>
> #include <string>
> -#include <iosfwd>
> +#include <bits/iosfwd.h>
> #include <limits>
> #include <debug/debug.h>
> #include <type_traits>
> diff --git a/libstdc++-v3/include/std/spanstream
> b/libstdc++-v3/include/std/spanstream
> index fbb40ff1db26..fd2a446ddaa3 100644
> --- a/libstdc++-v3/include/std/spanstream
> +++ b/libstdc++-v3/include/std/spanstream
> @@ -43,6 +43,7 @@
> #include <streambuf>
> #include <istream>
> #include <ostream>
> +#include <bits/iosfwd_span.h>
> #include <bits/ranges_base.h>
>
> namespace std _GLIBCXX_VISIBILITY(default)
> diff --git a/libstdc++-v3/include/std/sstream
> b/libstdc++-v3/include/std/sstream
> index 421c1f744b3d..1c491e16458e 100644
> --- a/libstdc++-v3/include/std/sstream
> +++ b/libstdc++-v3/include/std/sstream
> @@ -42,6 +42,7 @@
> #include <istream>
> #include <ostream>
>
> +#include <bits/iosfwd_string.h>
> #include <bits/alloc_traits.h> // allocator_traits, __allocator_like
>
> #define __glibcxx_want_sstream_from_string_view
> diff --git a/libstdc++-v3/include/std/streambuf
> b/libstdc++-v3/include/std/streambuf
> index d6036bd5ddc4..616e44f74a76 100644
> --- a/libstdc++-v3/include/std/streambuf
> +++ b/libstdc++-v3/include/std/streambuf
> @@ -40,7 +40,7 @@
> #include <bits/requires_hosted.h> // iostreams
>
> #include <bits/c++config.h>
> -#include <iosfwd>
> +#include <bits/iosfwd.h>
> #include <bits/localefwd.h>
> #include <bits/ios_base.h>
> #include <bits/cpp_type_traits.h>
> diff --git a/libstdc++-v3/include/std/string_view
> b/libstdc++-v3/include/std/string_view
> index efbf432f1129..81b0011245b5 100644
> --- a/libstdc++-v3/include/std/string_view
> +++ b/libstdc++-v3/include/std/string_view
> @@ -63,7 +63,7 @@
> #endif
>
> #if _GLIBCXX_HOSTED
> -# include <iosfwd>
> +# include <bits/iosfwd.h>
> # include <bits/ostream_insert.h>
> #endif
>
> diff --git a/libstdc++-v3/include/std/syncstream
> b/libstdc++-v3/include/std/syncstream
> index 29a44ba1d7af..9cecd513e9a5 100644
> --- a/libstdc++-v3/include/std/syncstream
> +++ b/libstdc++-v3/include/std/syncstream
> @@ -43,6 +43,7 @@
> #ifdef __cpp_lib_syncbuf // C++ >= 20 && HOSTED && CXX11ABI
> #include <sstream>
>
> +#include <bits/iosfwd_sync.h>
> #include <bits/alloc_traits.h>
> #include <bits/allocator.h>
> #include <bits/std_mutex.h>
> diff --git a/libstdc++-v3/include/std/system_error
> b/libstdc++-v3/include/std/system_error
> index 6fe63010e339..6dbef5ed45dc 100644
> --- a/libstdc++-v3/include/std/system_error
> +++ b/libstdc++-v3/include/std/system_error
> @@ -41,7 +41,7 @@
>
> #include <bits/c++config.h>
> #include <bits/error_constants.h>
> -#include <iosfwd>
> +#include <bits/iosfwd.h>
> #include <stdexcept>
> #if __cplusplus > 201703L
> # include <compare>
> --
> 2.54.0
>
>
