[PATCH v2] libstdc++: Fix std::system_category().message(int) on mingw32 target

[Wang Jinghao]

On 2026/1/10 20:50, Jonathan Wakely wrote:
> On Sat, 10 Jan 2026 at 12:24, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
>> On Sat, 10 Jan 2026 at 12:17, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
>>> On Sat, 10 Jan 2026 at 10:45, Wang Jinghao <zheng.xianyuwang@gmail.com> wrote:
>>>> On the mingw32 target, std::system_category().message(int) uses
>>>> FormatMessage api to format error messages. When the error message contains
>>>> insert sequences, it is unsafe not to use the FORMAT_MESSAGE_OGNORE_INSERTS
>>>> flag, as seen at:
>>>> https://devblogs.microsoft.com/oldnewthing/20071128-00/?p=24353
>>>>
>>>> The output of FormatMessage ends with "\r\n" and includes a Full stop character
>>>> used by the current thread's UI language. Now, we will remove "\r\n" and
>>>> any trailing '.' from the output in any language environment.
>>>>
>>>> In the testsuite for std::system_category().message(int), we first switch the
>>>> thread UI language to en-US tomeet expectations in any language environment.
>>> Thanks, the patch looks good now.
>>>
>>>> libstdc++-v3/ChangeLog:
>>>>
>>>>          * src/c++11/system_error.cc (system_error_category) [_WIN32]:
>>>>          Fix typo in __MINGW32__ macro name.
>>>>          Adjust behavior on the mingw32 target.
>>> The two lines above relate to the error_category/system_category.cc
>>> test, not the src/c++11/system_category.cc source file, right?


Sorry, I made a mistake. The correction for the __MINGW32__ macro

is in error_category/system_category.cc.


>>>>          Use FormatMessageA function instead of FormatMessage macro.
>>>>          * testsuite/19_diagnostics/error_category/system_category.cc:
>>>>          Adjust behavior on the mingw32 target.
>>> I've just noticed that there's no Signed-off-by trailer in the patch.
>>> Do you have a copyright assignment filed with the FSF?
>>>
>>> As documented at https://gcc.gnu.org/contribute.html#legal we need
>>> either a copyright assignment, or DCO sign-off.
>>>
>>> If you don't have a copyrigh assignment, could you please add the
>>> Signed-off-by trailer if you are willing and able to agree to the
>>> terms of https://gcc.gnu.org/dco.html ?
>> Actually, don't worry, I don't think this change can be considered
>> "legally significant", because the changes are small except for some
>> whitespace changes and typo fixes.
>>
>> So I'll push this to the git repo - thanks for fixing it!


Thank you for your reminder!


> Hmm, when I test this with mingw-w64 under Wine, I get:
>
> /home/jwakely/src/gcc/gcc/libstdc++-v3/testsuite/19_diagnostics/error_category/system_category.cc
> 01ec:fixme:nls:RtlSetThreadPreferredUILanguages 8, 00000001400A8122,
> 000000000021FE8C
> /home/jwakely/src/gcc/gcc/libstdc++-v3/testsuite/19_diagnostics/error_category/system_category.cc:127:
> void test03(): Assertion 'msg == "Access is denied"'
> failed.
> FAIL: /home/jwakely/src/gcc/gcc/libstdc++-v3/testsuite/19_diagnostics/error_category/system_category.cc
>
> Inspecting the 'msg' string, the content is "Access denied", which is
> what we have on trunk today.
>
> Can you confirm whether it should be "Access is denied" (as in your
> patch) or "Access denied"?

I apologize that I haven't tested it on Wine, but the the error message 
I encountered on my Windows 11 Version 10.0.26200 system was "Access is 
denied," which is the same as the one recorded in Microsoft Docs, see 
here: 
https://github.com/MicrosoftDocs/win32/blob/docs/desktop-src/Debug/system-error-codes--0-499-.md 
or 
https://winprotocoldoc.z19.web.core.windows.net/MS-ERREF/%5bMS-ERREF%5d.pdf 
This is probably because Wine is implemented differently than Microsoft 
Windows. :(

Perhaps we also need to add checks for the Wine environment, like those 
found at 
https://web.archive.org/web/20131028024505/https://www.winehq.org/pipermail/wine-devel/2008-September/069387.html