There are several ways to access locale information. The simplest way is to let the C library itself do the work. Several of the functions in this library implicitly access the locale data, and use what information is provided by the currently selected locale. This is how the locale model is meant to work normally.
As an example take the strftime function, which is meant to nicely
format date and time information (see Formatting Calendar Time).
Part of the standard information contained in the LC_TIME
category is the names of the months. Instead of requiring the
programmer to take care of providing the translations the
strftime function does this all by itself. %A
in the format string is replaced by the appropriate weekday
name of the locale currently selected by LC_TIME. This is an
easy example, and wherever possible functions do things automatically
in this way.
But there are quite often situations when there is simply no function
to perform the task, or it is simply not possible to do the work
automatically. For these cases it is necessary to access the
information in the locale directly. To do this the C library provides
two functions: localeconv and nl_langinfo. The former is
part of ISO C and therefore portable, but has a brain-damaged
interface. The second is part of the Unix interface and is portable in
as far as the system follows the Unix standards.