Set a locale for string collation routines. This controls alphabetic ordering in strcoll and strxfrm.
Set a locale for the ctype(3) and multibyte(3) functions. This controls recognition of upper and lower case, alphabetic or non-alphabetic characters, and so on.
Set a locale for message catalogs, see catopen(3) function.
Set a locale for formatting monetary values; this affects the localeconv function.
Set a locale for formatting numbers. This controls the formatting of decimal points in input and output of floating point numbers in functions such as printf and scanf, as well as values returned by localeconv.
Set a locale for formatting dates and times using the strftime function.
Only three locales are defined by default, the empty string "" "" " which denotes the native environment, and the "" "C" " and "" "POSIX" " locales, which denote the C language environment. A locale argument of NULL causes setlocale to return the current locale. By default, C programs start in the "" "C" " locale. The only function in the library that sets the locale is setlocale; the locale is never changed as a side effect of some other routine.