C localization functions: Difference between revisions

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{{C Standard Library}}

In [[computing]], '''C localization functions''' are a group of functions in the [[C (programming language)|C programming language]] implementing basic localization routines.<ref name="c99">{{cite book | url=http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf | title=ISO/IEC 9899:1999 specification | at=p. 204, § 7.11 ''Localization'' }}</ref><ref name="c_primer">{{cite book|title=C primer plus | first=Stephen | last=Prata | year=2004 | publisher=Sams Publishing | isbn=0-672-32696-5 | at=Appendix B, Section V: The Standard ANSI C Library with C99 Additions}}</ref> The functions are used in multilingual programs to adapt to the specific locale. In particular, the way of displaying of numbers and currency can be modified. These settings affect the behaviour of [[C file input/output | input/output functions]] in the C Standard Library.<ref>{{Cite web|url=http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf|title=ISO/IEC 9899:201x|date=12 April 2011|page=181|archive-url=https://web.archive.org/web/20180329042731/http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf|archive-date=29 March 2018|url-status=}}</ref>

==Overview of functions==

C localization functions and types are defined in <tt>{{mono|locale.h</tt>}} (<tt>{{mono|clocale</tt>}} header in C++).<ref name=www.utas.edu.au>{{cite web|title=locale.h|url=http://www.utas.edu.au/infosys/info/documentation/C/CStdLib.html#locale.h|work=utas.edu.au|publisher=infosys|accessdate=14 September 2011|archive-date=4 June 2012|archive-url=https://web.archive.org/web/20120604201614/http://www.utas.edu.au/infosys/info/documentation/C/CStdLib.html#locale.h|url-status=dead}}</ref><ref>{{Cite web|url=https://github.com/openbsd/src/blob/master/include/locale.h|title=openbsd/src|website=GitHub|language=en|access-date=2018-04-09}}</ref>

{| class="wikitable" style="font-size:0.85em;"

! Function

! Description

|-

! style="font-family:monospace" | {{anchor|setlocale}}<code>[http://en.cppreference.com/w/cppc/locale/setlocale setlocale]</code>

| sets and gets the current C locale

|-

! style="font-family:monospace" | {{anchor|localeconv}}<code>[http://en.cppreference.com/w/cppc/locale/localeconv localeconv]</code>

| returns numeric and monetary formatting details of the current locale

|-

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==Criticism==

C standard localization functions are criticized because the localization state is stored globally. This means that in a given program all operations involving a locale can use only one locale at a time. As a result, it is very difficult to implement programs that use more than one locale.<ref>{{cite web | title=The Standard C Locale and the Standard C++ Locales | url=http://www.math.hkbu.edu.hk/parallel/pgi/doc/pgC++_lib/stdlibug/sta_9169.htm | publisher=Rogue Wave Software, Inc. | year=1996 | access-date=10 November 2011 | archive-date=19 February 2020 | archive-url=https://web.archive.org/web/20200219173855/http://www.math.hkbu.edu.hk/parallel/pgi/doc/pgC++_lib/stdlibug/sta_9169.htm | url-status=dead }}</ref>

The functions alter the behavior of printf/scanf/strtod which are often used to write saved data to a file or to other programs. The result is that a saved file in one locale will not be readable in another locale, or not be readable ''at all'' due to assumptions such as "numbers end at comma characters". Most large-scale software forces the locale to "C" (or another fixed value) to work around these problems.

Another criticism is that these functions do not address at all the far more important problem of translating text to a different language. A solution that could substitute text strings could easily substitute printf format strings, if some extra %-sequences were added to control the ___location of commas this could achieve all the number formatting fixes in a far more obvious and easily-controlled way.

==Example==

<sourcesyntaxhighlight lang="cppc">

#include <stdio.h>

#include <stdlib.h>

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int main(void)

{

{ /* Locale is set to "C" before this. This call sets it

to the "current locale" by reading environment variables: */

setlocale(LC_ALL, "");

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currentlocale->currency_symbol);

return EXIT_SUCCESS;
}

</syntaxhighlight>

</source>

==See also==

*[[Locale (computer software)]]

==References==

{{Reflist}}

[[Category:C Standardstandard Librarylibrary]]

{{use dmy dates|January 2012}}

[[Category:C Standard Library]]

[[ru:Locale.h]]

[[uk:Locale.h]]