On Mon, Jul 13, 2026 at 7:15 PM Jonathan Wakely <[email protected]> wrote:
> We should not try to export names which are not declared if GCC is
> configured with --disable-wchar_t.
>
> We should also not define the wide stream aliases in <syncstream> and
> <spanstream>.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/126111
> * include/std/format (__format::__write_escape_seq): Move alias
> declaration into #ifdef _GLIBCXX_USE_WCHAR_T group.
> * include/std/spanstream (wspanbuf, wispanstream, wospanstream)
> (wspanstream): Only declare for _GLIBCXX_USE_WCHAR_T.
> * include/std/syncstream (wsyncbuf wosyncstream): Likewise.
> * src/c++23/std.cc.in: Add preprocessor checks for
> _GLIBCXX_USE_WCHAR_T to names which depend on it.
> ---
>
> Tested x86_64-linux.
>
Outside of single question below, this LGTM.
>
> libstdc++-v3/include/std/format | 2 +-
> libstdc++-v3/include/std/spanstream | 8 ++++++
> libstdc++-v3/include/std/syncstream | 5 ++--
> libstdc++-v3/src/c++23/std.cc.in | 44 ++++++++++++++++++++++++-----
> 4 files changed, 49 insertions(+), 10 deletions(-)
>
> diff --git a/libstdc++-v3/include/std/format
> b/libstdc++-v3/include/std/format
> index 1b4082e07a44..2530ecb58057 100644
> --- a/libstdc++-v3/include/std/format
> +++ b/libstdc++-v3/include/std/format
> @@ -1052,7 +1052,6 @@ namespace __format
> __write_escape_seq(_Out __out, uint_least32_t __val,
> basic_string_view<_CharT> __prefix)
> {
> - using _Str_view = basic_string_view<_CharT>;
>
Why do we need this change? The function should not be instantiated
with _CharT = wchar_t, so this should be OK.
> constexpr size_t __max = 8;
> char __buf[__max];
> const string_view __narrow(
> @@ -1067,6 +1066,7 @@ namespace __format
> #ifdef _GLIBCXX_USE_WCHAR_T
> else
> {
> + using _Str_view = basic_string_view<_CharT>;
>
If we go with this direction, simply replace _CharT with wchar_t
in line below, and _Str_view with wstring_view in __format_write.
> _CharT __wbuf[__max];
> const size_t __n = __narrow.size();
> std::__to_wstring_numeric(__narrow.data(), __n, __wbuf);
> diff --git a/libstdc++-v3/include/std/spanstream
> b/libstdc++-v3/include/std/spanstream
> index fd2a446ddaa3..6f1f681ae793 100644
> --- a/libstdc++-v3/include/std/spanstream
> +++ b/libstdc++-v3/include/std/spanstream
> @@ -225,7 +225,9 @@ template<typename _CharT, typename _Traits>
> { __x.swap(__y); }
>
> using spanbuf = basic_spanbuf<char>;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using wspanbuf = basic_spanbuf<wchar_t>;
> +#endif
>
> template<typename _CharT, typename _Traits>
> class basic_ispanstream
> @@ -319,7 +321,9 @@ template<typename _CharT, typename _Traits>
> { __x.swap(__y); }
>
> using ispanstream = basic_ispanstream<char>;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using wispanstream = basic_ispanstream<wchar_t>;
> +#endif
>
> template<typename _CharT, typename _Traits>
> class basic_ospanstream
> @@ -389,7 +393,9 @@ template<typename _CharT, typename _Traits>
> { __x.swap(__y); }
>
> using ospanstream = basic_ospanstream<char>;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using wospanstream = basic_ospanstream<wchar_t>;
> +#endif
>
> template<typename _CharT, typename _Traits>
> class basic_spanstream
> @@ -459,7 +465,9 @@ template<typename _CharT, typename _Traits>
> { __x.swap(__y); }
>
> using spanstream = basic_spanstream<char>;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using wspanstream = basic_spanstream<wchar_t>;
> +#endif
>
> _GLIBCXX_END_NAMESPACE_VERSION
> } // namespace std
> diff --git a/libstdc++-v3/include/std/syncstream
> b/libstdc++-v3/include/std/syncstream
> index 9cecd513e9a5..7a1f956dca55 100644
> --- a/libstdc++-v3/include/std/syncstream
> +++ b/libstdc++-v3/include/std/syncstream
> @@ -299,10 +299,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> { __x.swap(__y); }
>
> using syncbuf = basic_syncbuf<char>;
> - using wsyncbuf = basic_syncbuf<wchar_t>;
> -
> 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 std
> #endif // __cpp_lib_syncbuf
> diff --git a/libstdc++-v3/src/c++23/std.cc.in b/libstdc++-v3/src/c++23/
> std.cc.in
> index dbed0112dca5..5aab08f2c498 100644
> --- a/libstdc++-v3/src/c++23/std.cc.in
> +++ b/libstdc++-v3/src/c++23/std.cc.in
> @@ -1368,17 +1368,19 @@ export namespace std
> #endif
> using std::formatter;
> using std::make_format_args;
> - using std::make_wformat_args;
> #if __cpp_lib_format >= 202603L // >= C++26
> using std::dynamic_format;
> #endif
> using std::vformat;
> using std::vformat_to;
> using std::visit_format_arg;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> + using std::make_wformat_args;
> using std::wformat_args;
> using std::wformat_context;
> using std::wformat_parse_context;
> using std::wformat_string;
> +#endif
> #ifdef __cpp_lib_format_ranges
> using std::format_kind;
> using std::range_format;
> @@ -1416,10 +1418,12 @@ export namespace std
> using std::ifstream;
> using std::ofstream;
> using std::swap;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wfilebuf;
> using std::wfstream;
> using std::wifstream;
> using std::wofstream;
> +#endif
> }
>
> // <functional>
> @@ -1620,7 +1624,9 @@ export namespace std
> using std::streamsize;
> using std::unitbuf;
> using std::uppercase;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wios;
> +#endif
> }
>
> // <iosfwd>
> @@ -1639,9 +1645,11 @@ export namespace std
> using std::basic_syncbuf;
> using std::osyncstream;
> using std::syncbuf;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wosyncstream;
> using std::wsyncbuf;
> #endif
> +#endif
> }
>
> // <iostream>
> @@ -1651,10 +1659,12 @@ export namespace std
> using std::cin;
> using std::clog;
> using std::cout;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wcerr;
> using std::wcin;
> using std::wclog;
> using std::wcout;
> +#endif
> }
>
> // <istream>
> @@ -1664,8 +1674,10 @@ export namespace std
> using std::basic_istream;
> using std::iostream;
> using std::istream;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wiostream;
> using std::wistream;
> +#endif
> using std::ws;
> using std::operator>>;
> }
> @@ -2487,7 +2499,9 @@ export namespace std
> using std::ends;
> using std::flush;
> using std::ostream;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wostream;
> +#endif
> using std::operator<<;
> #ifdef __cpp_lib_syncbuf
> using std::emit_on_flush;
> @@ -2916,9 +2930,11 @@ export namespace std
> using std::ssub_match;
> using std::sub_match;
> using std::swap;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wcsub_match;
> using std::wregex;
> using std::wssub_match;
> +#endif
> using std::operator==;
> using std::operator<=>;
> using std::operator<<;
> @@ -2934,20 +2950,24 @@ export namespace std
> using std::smatch;
> using std::sregex_iterator;
> using std::sregex_token_iterator;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wcmatch;
> using std::wcregex_iterator;
> using std::wcregex_token_iterator;
> using std::wsmatch;
> using std::wsregex_iterator;
> using std::wsregex_token_iterator;
> +#endif
> namespace pmr
> {
> #if _GLIBCXX_USE_CXX11_ABI
> using std::pmr::cmatch;
> using std::pmr::match_results;
> using std::pmr::smatch;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::pmr::wcmatch;
> using std::pmr::wsmatch;
> +#endif
> #endif
> }
> }
> @@ -3020,17 +3040,19 @@ export namespace std
> export namespace std
> {
> using std::basic_spanbuf;
> - using std::spanbuf;
> - using std::wspanbuf;
> using std::basic_ispanstream;
> - using std::ispanstream;
> - using std::wispanstream;
> using std::basic_ospanstream;
> - using std::ospanstream;
> - using std::wospanstream;
> using std::basic_spanstream;
> + using std::spanbuf;
> + using std::ispanstream;
> + using std::ospanstream;
> using std::spanstream;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> + using std::wspanbuf;
> + using std::wispanstream;
> + using std::wospanstream;
> using std::wspanstream;
> +#endif
> }
> #endif
>
> @@ -3046,10 +3068,12 @@ export namespace std
> using std::stringbuf;
> using std::stringstream;
> using std::swap;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wistringstream;
> using std::wostringstream;
> using std::wstringbuf;
> using std::wstringstream;
> +#endif
> }
>
> // <stack>
> @@ -3144,7 +3168,9 @@ export namespace std
> {
> using std::basic_streambuf;
> using std::streambuf;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wstreambuf;
> +#endif
> }
>
> // <string>
> @@ -3171,7 +3197,9 @@ export namespace std
> using std::stoull;
> using std::string;
> using std::to_string;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::to_wstring;
> +#endif
> using std::u16string;
> using std::u32string;
> using std::u8string;
> @@ -3236,9 +3264,11 @@ export namespace std
> using std::basic_osyncstream;
> using std::osyncstream;
> using std::syncbuf;
> +#ifdef _GLIBCXX_USE_WCHAR_T
> using std::wosyncstream;
> using std::wsyncbuf;
> #endif
> +#endif
> }
>
> // 19.5 <system_error>
> --
> 2.55.0
>
>
