[PATCH] libstdc++: Fix std module to work with --disable-wchar_t [PR126111]
Tomasz Kaminski
tkaminsk@redhat.com
Tue Jul 21 04:53:04 GMT 2026
On Tue, Jul 14, 2026 at 9:22 AM Jonathan Wakely <jwakely.gcc@gmail.com>
wrote:
>
>
> On Tue, 14 Jul 2026, 08:21 Jonathan Wakely, <jwakely.gcc@gmail.com> wrote:
>
>>
>>
>> On Tue, 14 Jul 2026, 08:15 Tomasz Kaminski, <tkaminsk@redhat.com> wrote:
>>
>>>
>>>
>>> On Mon, Jul 13, 2026 at 7:15 PM Jonathan Wakely <jwakely@redhat.com>
>>> 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.
>>>
>> Should we backport this to GCC-16?
>
>>>> 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.
>>>
>>
>> Because it gives a -Wunused-local-typedef warning when the WCHAR_T macro
>> is undefined.
>>
>
> I'll change it to wstring_view.
>
>
>
>
>>
>> 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
>>>>
>>>>
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