C++ In a Nutshell

<clocale>

The <clocale> header (from the C standard <locale.h> header) declares types and functions to support internationalization and localization for the C standard library. C++ also offers <locale>, which has more flexibility and functionality, but at a cost of complexity and overhead.

The various locale settings are grouped into categories. Each category has a macro (named LC_ category) to identify the category in a call to setlocale. Ordinarily, you would use LC_ALL to set all the categories at once, but you can pick a category from one locale and another category from a different locale.