libstdc++ features like stacktrace, text_encoding, time zone and locale are not working correctly

[Shuangcheng-Ni]

stacktrace & text_encoding

stacktrace and text_encoding are not enabled by default.

PS > g++ -std=c++26 -x c++ - -lstdc++exp
#include <stacktrace>
#include <text_encoding>

int main()
{
    std::stacktrace::current();
    std::text_encoding::environment();
}
^Z
<stdin>: In function 'int main()':
<stdin>:6:10: error: 'std::stacktrace' has not been declared
<stdin>:7:10: error: 'std::text_encoding' has not been declared

If I force enable them, I will get link errors.

PS > g++ -std=c++26 -x c++ - -lstdc++exp
#define __cpp_lib_stacktrace
#define __cpp_lib_text_encoding
#include <stacktrace>
#include <text_encoding>

int main()
{
    std::stacktrace::current();
    std::text_encoding::environment();
}
^Z
.../mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\...\AppData\Local\Temp\ccuMXIMp.o:<stdin>:(.text+0x3f): undefined reference to `std::text_encoding::environment()'
.../mingw64/bin/../lib/gcc/x86_64-w64-mingw32/14.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: C:\Users\...\AppData\Local\Temp\ccuMXIMp.o:<stdin>:(.text$_ZNSt16basic_stacktraceISaISt16stacktrace_entryEE7currentERKS1_[_ZNSt16basic_stacktraceISaISt16stacktrace_entryEE7currentERKS1_]+0x59): undefined reference to `std::__stacktrace_impl::_S_current(int (*)(void*, unsigned long long), void*, int)'
collect2.exe: error: ld returned 1 exit status

The error is caused by the lack of related functions in libstdc++exp.a.

PS > nm .\mingw64\lib\libstdc++exp.a | sls 'stacktrace.o|text_encoding.o' -Context 0, 5

> stacktrace.o:
  0000000000000000 b .bss
  0000000000000000 d .data
  0000000000000000 r .rdata$zzz
  0000000000000000 t .text

> text_encoding.o:
  0000000000000000 b .bss
  0000000000000000 d .data
  0000000000000000 r .rdata$zzz
  0000000000000000 t .text

time zone & locale

std::chrono::current_zone() from libstdc++ always returns UTC, while its C-style equivalent std::localtime from ucrt/msvcrt works correctly.

PS > g++ -std=c++26 -x c++ - -lstdc++exp
#include <chrono>
#include <iostream>
#include <print>

using namespace std::literals;

int main()
{
    std::chrono::sys_days   tp{ 2025y / 1 / 1 };
    std::chrono::zoned_time zt(std::chrono::current_zone(), tp);
    std::println("{:%F %T %z (%Z)}", zt);

    auto t{ std::chrono::system_clock::to_time_t(tp) };
    std::cout << std::put_time(std::localtime(&t), "%F %T %z (%Z)") << std::endl;
}
^Z

PS > .\a.exe
2025-01-01 00:00:00 +0000 (UTC)
2024-12-31 18:00:00 -0600 (中部标准时间)

std::locale from libstdc++ only accepts nullptr, C and POSIX, while its C-style equivalent std::setlocale from ucrt/msvcrt works correctly.

PS > g++ -std=c++26 -x c++ - -lstdc++exp
#include <iostream>
#include <locale>
#include <print>

int main()
{
    constexpr std::wstring_view s{ L"aα啊" };

    const char *locales[]{ nullptr, "C", "POSIX", "", "zh_CN.UTF-8" };

    for (auto locale : locales)
    {
        std::println("locale: \"{}\"", locale ? locale : "nullptr");

        std::println("C++");
        try
        {
            std::locale::global(locale ? std::locale(locale) : std::locale{});
            std::wcout << s << std::endl;
        }
        catch (std::exception &e)
        {
            std::println("exception: {}", e.what());
        }
        std::println("wcout.good(): {}", std::wcout.good());
        std::wcout.clear();

        std::println("C");
        std::setlocale(LC_ALL, locale);
        std::wcout << s << std::endl;
        std::println("wcout.good(): {}", std::wcout.good());
        std::wcout.clear();

        std::println();
    }
}
^Z

PS > .\a.exe
locale: "nullptr"
C++
awcout.good(): false
C
awcout.good(): false

locale: "C"
C++
awcout.good(): false
C
awcout.good(): false

locale: "POSIX"
C++
awcout.good(): false
C
awcout.good(): false

locale: ""
C++
exception: locale::facet::_S_create_c_locale name not valid
wcout.good(): true
C
aα啊
wcout.good(): true

locale: "zh_CN.UTF-8"
C++
exception: locale::facet::_S_create_c_locale name not valid
wcout.good(): true
C
aα啊
wcout.good(): true

Linux side status

All these features work correctly on Linux side. These issues are MinGW-only.

[brechtsanders]

I'm not sure how I can help here as I just build GCC+MinGW-w64.

The best way forward is probably to report these issues in separate bug reports to the GCC and/or MinGW-w64 developers.