std::wcout fails to output wide Unicode strings even when a suitable C locale is setΒ #158430
Description
Test code (CE):
#include <cstdio>
#include <iostream>
namespace my {
template <class CharT>
std::basic_ios<CharT> &check_ios(std::basic_ios<CharT> &ios) {
if (ios) {
return ios;
}
auto state = ios.rdstate();
using std::ios_base;
std::cerr << "eofbit: " << ((state & ios_base::eofbit) != 0) << '\n';
std::cerr << "failbit: " << ((state & ios_base::failbit) != 0) << '\n';
std::cerr << "badbit: " << ((state & ios_base::badbit) != 0) << '\n';
std::terminate();
}
template <auto Error> auto check(auto result) {
if (result != Error) {
return result;
}
std::terminate();
}
} // namespace my
int main() {
constexpr auto wide_test = L"Ο|π|β¬";
#if TEST == 1 // Test C++ locale
std::ios_base::sync_with_stdio(false);
std::wcout.imbue(std::locale{"en_US.UTF-8"});
std::wcout << wide_test << '\n' << my::check_ios;
// - β
libc++:
// - returned: 0
// - stdout:
// - Ο|π|β¬
// - β
libstdc++:
// - returned: 0
// - stdout:
// - Ο|π|β¬
#elif TEST == 2 // Test C locale
my::check<nullptr>(std::setlocale(LC_ALL, "en_US.UTF-8"));
my::check<EOF>(std::fputws(wide_test, stdout));
my::check<WEOF>(std::putwchar(L'\n'));
std::wcout << wide_test << '\n' << my::check_ios;
// - β libc++:
// - returned: 139
// - stdout:
// - Ο|π|β¬
// - stderr:
// - eofbit: 0
// - failbit: 1
// - badbit: 1
// - libc++abi: terminating
// - Program terminated with signal: SIGSEGV
// - β
libstdc++:
// - returned: 0
// - stdout:
// - Ο|π|β¬
// - Ο|π|β¬
#endif
}In Test 2 above, since sync_with_stdio(false) is not called, std::wcout should remain synchronized with stdout. In other words, it should behave similarly to the C-style I/O functions (e.g., std::fputws). After setting the C locale, std::fputws can correctly output wide Unicode strings, so there seems to be little reason why std::wcout cannot follow suit in this case.