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Date: Thu, 21 Sep 2023 12:08:26 -0600
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Subject: Re: std::runtime_error on std::locale("")
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From: Brian Inglis via Cygwin <cygwin AT cygwin DOT com>
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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)

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry

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