The setlocale() function is used to set or query the program's current locale.
If locale is not NULL, the program's current locale is modified according to the arguments. The argument category determines which parts of the program's current locale should be modified.
for all of the locale.
for regular expression matching (it determines the meaning of range expressions and equivalence classes) and string collation.
for regular expression matching, character classification, conversion, case-sensitive comparison, and wide character functions.
for localizable natural-language messages.
for monetary formatting.
for number formatting (such as the decimal point and the thousands separator).
for time and date formatting.
The argument locale is a pointer to a character string containing the required setting of category. Such a string is either a well-known constant like ''setlocale__.
If locale is , each part of the locale that should be modified is set according to the environment variables. The details are implementation dependent. For glibc, first (regardless of category), the environment variable LC_ALL is inspected, next the environment variable with the same name as the category (LC_COLLATE, LC_CTYPE, LC_MESSAGES, LC_MONETARY, LC_NUMERIC, LC_TIME) and finally the environment variable LANG. The first existing environment variable is used. If its value is not a valid locale specification, the locale is unchanged, and setlocale returns NULL.
The locale or is a portable locale; its LC_CTYPE part corresponds to the 7-bit ASCII character set.
A locale name is typically of the form language[_''territory''?[.''codeset''?[@''modifier''?, where language is an ISO 639 language code, territory is an ISO 3166 country code, and codeset is a character set or encoding identifier like ISO-8859-1 or UTF-8. For a list of all supported locales, try locale(1).
If locale is NULL, the current locale is only queried, not modified.