Brian Inglis via Cygwin wrote:
On 2023-09-21 10:28, Takashi Yano via Cygwin wrote:
On Fri, 22 Sep 2023 01:12:04 +0900
Takashi Yano wrote:
I wonder why the following code throws std::runtime_error
even though the LC_ALL is set to valid locale other than "C".
This does not occur only when LC_ALL is set to "C".
#include <locale>
int main()
{
std::locale("");
return 0;
}
In linux, this occurs only when the LC_ALL is set to invalid
locale (i.e. locale that is not registered in system).
Similarly,
std::locale("ja_JP.UTF-8")
throws std::runtime_error in cygwin.
Looks like the implementation does not like any default "" or explicit
"en_US.UTF-8" strings there! See example at link and below; results
are always the same:
https://en.cppreference.com/w/cpp/locale/locale
#include <iostream>
#include <locale>
int main()
{
std::wcout << "User-preferred locale setting is "
<< std::locale().name().c_str() << '\n';
// on startup, the global locale is the "C" locale
std::wcout << 1000.01 << '\n';
// replace the C++ global locale and the "C" locale with the
user-preferred locale
std::locale::global(std::locale(""));
// use the new global locale for future wide character output
std::wcout.imbue(std::locale());
// output the same number again
std::wcout << 1000.01 << '\n';
}
$ g++ -o c++locale{,.cc}
$ ./c++locale
User-preferred locale setting is C
1000.01
terminate called after throwing an instance of 'std::runtime_error'
what(): locale::facet::_S_create_c_locale name not valid
Aborted (core dumped)
According to libstdc++ source, the internal function
locale::facet::_S_create_c_locale() calls some __newlocale() which
apparently does not arrive at newlocale() from cygwin1.dll. But
cygstdc++-6.dll imports newlocale() from cygwin1.dll.
Only standard locale "C" and its alias "POSIX" work with C++ std::locale().
The cygwin1.dll function newlocale() works as expected - except that it
does not set errno if the locale name is invalid.
--
Regards,
Christian
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