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libstdc++: Fix std::system_category().message(int) on mingw32 target

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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 to meet expectations in any
language environment.

libstdc++-v3/ChangeLog:

	* src/c++11/system_error.cc (system_error_category) [_WIN32]:
	Use FormatMessageA function instead of FormatMessage macro.
	* testsuite/19_diagnostics/error_category/system_category.cc:
	Fix typo in __MINGW32__ macro name.  Adjust behavior on the
	mingw32 target.
This commit is contained in:
Wang Jinghao
2026-01-10 18:43:14 +08:00
committed by Jonathan Wakely
parent 3ebe697f32
commit 972be84265
2 changed files with 27 additions and 13 deletions
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21
libstdc++-v3/src/c++11/system_error.cc
View File

@@ -161,22 +161,23 @@ namespace
#if defined(_WIN32) && !defined(__CYGWIN__)
char* buf = nullptr;
auto len
= FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM
| FORMAT_MESSAGE_ALLOCATE_BUFFER,
nullptr,
i,
LANG_USER_DEFAULT,
reinterpret_cast<LPTSTR>(&buf),
0,
nullptr);
= FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM
| FORMAT_MESSAGE_ALLOCATE_BUFFER
| FORMAT_MESSAGE_IGNORE_INSERTS,
nullptr,
i,
LANG_USER_DEFAULT,
reinterpret_cast<LPTSTR>(&buf),
0,
nullptr);
if (len > 0)
{
struct deleter {
void operator()(void* p) const { ::LocalFree(p); }
};
std::unique_ptr<char[], deleter> guard(buf);
if (len > 3 && !__builtin_memcmp(buf + len - 3, ".\r\n", 3)) [[likely]]
len -= 3;
if (len > 2 && !__builtin_memcmp (buf + len - 2, "\r\n", 2)) [[likely]]
len -= 2 + (buf[len - 3] == '.');
return string(buf, len);
}
return string("Unknown error code");

19
libstdc++-v3/testsuite/19_diagnostics/error_category/system_category.cc
View File

@@ -21,6 +21,11 @@
#include <locale>
#include <testsuite_hooks.h>
#if defined __MINGW32__ || defined __MINGW64__
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#endif
void
test01()
{
@@ -34,7 +39,7 @@ test02()
const std::error_category& cat = std::system_category();
std::error_condition cond;
#if defined __MING32__ || defined __MINGW64__
#if defined __MINGW32__ || defined __MINGW64__
cond = cat.default_error_condition(8); // ERROR_NOT_ENOUGH_MEMORY
VERIFY( cond.value() == ENOMEM );
VERIFY( cond.category() == std::generic_category() );
@@ -112,9 +117,17 @@ test03()
// set "C" locale to get expected message
auto loc = std::locale::global(std::locale::classic());
#if defined __MING32__ || defined __MINGW64__
#if defined __MINGW32__ || defined __MINGW64__
// On Windows, set thread preferred UI languages to "en-US"
// to get expected message
ULONG num_langs = 1;
SetThreadPreferredUILanguages(MUI_LANGUAGE_NAME, L"en-US\0", &num_langs);
std::string msg = std::system_category().message(5); // ERROR_ACCESS_DENIED
VERIFY(msg == "Access denied");
// Windows returns "Access is denied" but Wine returns "Access denied".
VERIFY(msg == "Access is denied" || msg == "Access denied");
SetThreadPreferredUILanguages(MUI_RESET_FILTERS, nullptr, nullptr);
#else
std::string msg = std::system_category().message(EBADF);
VERIFY( msg.find("file") != std::string::npos );