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Hi folks,
I've been investigating i18n of time/date formatting with the standard
C and C++ libraries. However, I've run into an issue with wide
character output. The documentation doesn't elaborate on what
encoding is used (or even how to specify one), so I hope someone might
have an idea?
The program listed below demonstrates the use of wcsftime() and
std::time_put<wchar_t> which is a C++ wrapper around it. I'm not sure
if this is a platform-dependent feature or part of the C standard.
I've compiled with GCC 3.4.3 on GNU/Linux, and run in an en_GB UTF-8
locale (note GCC 3.3.x won't work with wide streams at all well). The
output looks like this:
$ ./date3
asctime: Fri Nov 26 13:26:48 2004
strftime: Fri 26 Nov 2004 13:26:48 GMT
wcsftime: Fri 26 Nov 2004 13:26:48 GMT
std::time_put<char>: Fri 26 Nov 2004 13:26:48 GMT
std::time_put<wchar_t>: Fri 26 Nov 2004 13:26:48 GMT
Everything worked. It also works if I run in a different locale (all
locales use UTF-8 as their codeset):
$ LANG=de_DE LC_ALL=de_DE ./date3
asctime: Fri Nov 26 13:28:03 2004
strftime: Fr 26 Nov 2004 13:28:03 GMT
wcsftime: Fr 26 Nov 2004 13:28:03 GMT
std::time_put<char>: Fr 26 Nov 2004 13:28:03 GMT
std::time_put<wchar_t>: Fr 26 Nov 2004 13:28:03 GMT
$ LANG=pt_BR LC_ALL=pt_BR ./date3
asctime: Fri Nov 26 13:29:18 2004
strftime: Sex 26 Nov 2004 13:29:18 GMT
wcsftime: Sex 26 Nov 2004 13:29:18 GMT
std::time_put<char>: Sex 26 Nov 2004 13:29:18 GMT
std::time_put<wchar_t>: Sex 26 Nov 2004 13:29:18 GMT
However, if I use a locale where the output includes non-ASCII
characters, I get this:
asctime: Fri Nov 26 13:30:08 2004
strftime: ÐÑÐ 26 ÐÐÑ 2004 13:30:08
wcsftime: ^_B= 26 ^]>O 2004 13:30:08
std::time_put<char>: ÐÑÐ 26 ÐÐÑ 2004 13:30:08
std::time_put<wchar_t>: ^_B= 26 ^]>O 2004 13:30:08
Viewed as hexadecimal (aligned for comparison):
"Narrow" UTF-8:
Ð Ñ Ð 2 6 Ð Ð Ñ
==> d0 9f d1 82 d0 bd 20 32 36 20 d0 9d d0 be d1 8f
2 0 0 4 1 1 : 3 2 : 4 7 \n
==> 20 32 30 30 34 20 31 31 3a 35 31 3a 30 34 0a
"Wide" (unknown):
B = 2 6 > O
==> 1f 42 3d 20 32 36 20 1d 3e 4f
2 0 0 4 1 1 : 3 2 : 4 7 \n
==> 20 32 30 30 34 20 31 31 3a 35 31 3a 30 34 0a
In this case the "narrow" and "wide" outputs differ. The "narrow"
output is valid UTF-8, whereas the "wide" output is something
different entirely. What encoding does wcsftime() use when outputting
characters outside the ASCII range? UCS-4? Something
implementation-defined? I expected that both would result in readable
output; is this assumption incorrect?
My question is basically this: what is wcsftime() actually doing, and
how should I get printable output from the wide string it fills for
me? If I'm plunging into the realms of non-portability by even
considering using wide characters, are they worth considering to use?
Also, can gettext be used with wide characters?
Many thanks,
Roger
#include <iostream>
#include <locale>
#include <ctime>
#include <cwchar>
int main()
{
// Set up locale stuff...
std::locale::global(std::locale(""));
std::cout.imbue(std::locale());
std::wcout.imbue(std::locale());
// Get current time
time_t simpletime = time(0);
// Break down time.
std::tm brokentime;
localtime_r(&simpletime, &brokentime);
// Normalise.
mktime(&brokentime);
std::cout << "asctime: " << asctime(&brokentime);
// Print with strftime(3)
char buffer[40];
std::strftime(&buffer[0], 40, "%c", &brokentime);
std::cout << "strftime: " << &buffer[0] << '\n';
wchar_t wbuffer[40];
std::wcsftime(&wbuffer[0], 40, L"%c", &brokentime);
std::wcout << L"wcsftime: " << &wbuffer[0] << L'\n';
// Try again, but use proper locale facets...
const std::time_put<char>& tp =
std::use_facet<std::time_put<char> >(std::cout.getloc());
std::string pattern("std::time_put<char>: %c\n");
tp.put(std::cout, std::cout, std::cout.fill(),
&brokentime, &*pattern.begin(), &*pattern.end());
// And again, but using wchar_t...
const std::time_put<wchar_t>& wtp =
std::use_facet<std::time_put<wchar_t> >(std::wcout.getloc());
std::wstring wpattern(L"std::time_put<wchar_t>: %c\n");
wtp.put(std::wcout, std::wcout, std::wcout.fill(),
&brokentime, &*wpattern.begin(), &*wpattern.end());
return 0;
}
- --
Roger Leigh
Printing on GNU/Linux? http://gimp-print.sourceforge.net/
Debian GNU/Linux http://www.debian.org/
GPG Public Key: 0x25BFB848. Please sign and encrypt your mail.
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--
Linux-UTF8: i18n of Linux on all levels
Archive: http://mail.nl.linux.org/linux-utf8/
