The setlocale() function selects the appropriate piece of the program's locale as specified by the category and locale arguments. The category argument may have the following values: LC_CTYPE, LC_NUMERIC, LC_TIME, LC_COLLATE, LC_MONETARY, LC_MESSAGES, and LC_ALL. These names are defined in the <locale.h> header. The LC_ALL variable names all of a program's locale categories.
The LC_CTYPE variable affects the behavior of character handling functions such as isdigit(3C) and tolower(3C), and multibyte character functions such as mbtowc(3C) and wctomb(3C).
The LC_NUMERIC variable affects the decimal point character and thousands separator character for the formatted input/output functions and string conversion functions.
The LC_TIME variable affects the date and time format as delivered by ascftime(3C) cftime(3C) getdate(3C) strftime(3C) and strptime(3C)
The LC_COLLATE variable affects the sort order produced by collating functions such as strcoll (3C) and strxfrm(3C)
The LC_MONETARY variable affects the monetary formatted information returned by localeconv(3C).
The LC_MESSAGES variable affects the behavior of messaging functions such as dgettext(3C), gettext(3C), and gettxt(3C).
A value of "C" for locale specifies the traditional UNIX system behavior. At program startup, the equivalent of
is executed. This has the effect of initializing each category to the locale described by the environment "C".
A value of "" for locale specifies that the locale should be taken from environment variables. The order in which the environment variables are checked for the various categories
is given below:
|Category||1st Env Var||2nd Env Var||3rd Env Var
If a pointer to a string is given for locale, setlocale() attempts to set the locale for the given category to locale. If setlocale() succeeds, locale is returned. If setlocale() fails, a null pointer is returned and the program's locale is not changed.
For category LC_ALL, the behavior is slightly different. If a pointer to a string is given for locale and LC_ALL is given for category, setlocale() attempts to set the locale for all the categories to locale. The locale may be a simple locale, consisting of a
single locale, or a composite locale. If the locales for all the categories are the same after all the attempted locale changes, setlocale() will return a pointer to the common simple
locale. If there is a mixture of locales among the categories, setlocale() will return a composite locale.