[PATCH] libstdc++: Fix std module to work with --disable-wchar_t [PR126111]
Jonathan Wakely
jwakely.gcc@gmail.com
Tue Jul 14 07:22:17 GMT 2026
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.
>>
>>>
>>> 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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