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SETLOCALE(3) Library Functions Manual SETLOCALE(3)

setlocale, localeconv — natural language formatting for C

#include <locale.h>

char *
setlocale(int category, const char *locale);

struct lconv *
localeconv(void);

The () function sets the C library's notion of natural language formatting style for particular sets of routines. Each such style is called a “locale” and is invoked using an appropriate name passed as a C string. The localeconv() routine returns the current locale's parameters for formatting numbers.

The () function recognizes several categories of routines. These are the categories and the sets of routines they select:

Set the entire locale generically.
Set a locale for string collation routines. This controls alphabetic ordering in () and ().
Set a locale for the ctype(3) functions. This controls recognition of upper and lower case, alphabetic or non-alphabetic characters, and so on. The real work is done by the () 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 () and (), as well as values returned by localeconv().
Set a locale for formatting dates and times using the () 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 () 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.

The () function returns a pointer to a structure which provides parameters for formatting numbers, especially currency values:

struct lconv {
	char	*decimal_point;
	char	*thousands_sep;
	char	*grouping;
	char	*int_curr_symbol;
	char	*currency_symbol;
	char	*mon_decimal_point;
	char	*mon_thousands_sep;
	char	*mon_grouping;
	char	*positive_sign;
	char	*negative_sign;
	char	int_frac_digits;
	char	frac_digits;
	char	p_cs_precedes;
	char	p_sep_by_space;
	char	n_cs_precedes;
	char	n_sep_by_space;
	char	p_sign_posn;
	char	n_sign_posn;
	char	int_p_cs_precedes;
	char	int_p_sep_by_space;
	char	int_n_cs_precedes;
	char	int_n_sep_by_space;
	char	int_p_sign_posn;
	char	int_n_sign_posn;
};

The individual fields have the following meanings:

decimal_point
The decimal point character, except for currency values.
thousands_sep
The separator between groups of digits before the decimal point, except for currency values.
grouping
The sizes of the groups of digits, except for currency values. This is a pointer to a vector of integers, each of size char, representing group size from low order digit groups to high order (right to left). The list may be terminated with 0 or CHAR_MAX. If the list is terminated with 0, the last group size before the 0 is repeated to account for all the digits. If the list is terminated with CHAR_MAX, no more grouping is performed.
int_curr_symbol
The standardized international currency symbol.
currency_symbol
The local currency symbol.
mon_decimal_point
The decimal point character for currency values.
mon_thousands_sep
The separator for digit groups in currency values.
mon_grouping
Like grouping but for currency values.
positive_sign
The character used to denote non-negative currency values, usually the empty string.
negative_sign
The character used to denote negative currency values, usually a minus sign.
int_frac_digits
The number of digits after the decimal point in an international-style currency value.
frac_digits
The number of digits after the decimal point in the local style for currency values.
p_cs_precedes
1 if the currency symbol precedes the currency value for non-negative values, 0 if it follows.
p_sep_by_space
1 if a space is inserted between the currency symbol and the currency value for non-negative values, 0 otherwise.
n_cs_precedes
Like p_cs_precedes but for negative values.
n_sep_by_space
Like p_sep_by_space but for negative values.
p_sign_posn
The location of the positive_sign with respect to a non-negative quantity and the currency_symbol, coded as follows:

Parentheses around the entire string.
Before the string.
After the string.
Just before currency_symbol.
Just after currency_symbol.
n_sign_posn
Like p_sign_posn but for negative currency values.
int_p_cs_precedes
Like p_cs_precedes but for the international symbol.
int_n_cs_precedes
Like n_cs_precedes but for the international symbol.
int_p_sep_by_space
Like p_sep_by_space but for the international symbol.
int_n_sep_by_space
Like n_sep_by_space but for the international symbol.
int_p_sign_posn
Like p_sign_posn but for the international symbol.
int_n_sign_posn
Like n_sign_posn but for the international symbol.

Unless mentioned above, an empty string as a value for a field indicates a zero length result or a value that is not in the current locale. A CHAR_MAX result similarly denotes an unavailable value.

The setlocale() function returns NULL and fails to change the locale if the given combination of category and locale makes no sense. The localeconv() function returns a pointer to a static object which may be altered by later calls to setlocale() or localeconv().

mklocale(1), strcoll(3), strxfrm(3)

The setlocale() and localeconv() functions conform to ANSI X3.159-1989 (“ANSI C89”).

The setlocale() and localeconv() functions first appeared in 4.4BSD.

The current implementation supports only the "C" and "POSIX" locales for all but the LC_CTYPE locale.

In spite of the gnarly currency support in localeconv(), the standards don't include any functions for generalized currency formatting.

LC_COLLATE does not make sense for many languages. Use of LC_MONETARY could lead to misleading results until we have a real time currency conversion function. LC_NUMERIC and LC_TIME are personal choices and should not be wrapped up with the other categories.

July 14, 2014 OpenBSD-5.6