newlocale, freelocale - create, modify, and free a locale object

#include <locale.h>
locale_t newlocale(int category_mask, const char *locale,
 locale_t base);
void freelocale(locale_t locobj);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

    Since glibc 2.10:
        _XOPEN_SOURCE >= 700
    Before glibc 2.10:
        _GNU_SOURCE

The newlocale() function creates a new locale object, or modifies an existing object, returning a reference to the new or modified object as the function result. Whether the call creates a new object or modifies an existing object is determined by the value of base:

• If base is (locale_t) 0, a new object is created.

• If base refers to valid existing locale object (i.e., an object returned by a previous call to newlocale() or duplocale(3)), then that object is modified by the call. If the call is successful, the contents of base are unspecified (in particular, the object referred to by base may be freed, and a new object created). Therefore, the caller should ensure that it stops using base before the call to newlocale(), and should subsequently refer to the modified object via the reference returned as the function result. If the call fails, the contents of base remain valid and unchanged.

If base is the special locale object LC_GLOBAL_LOCALE (see duplocale(3)), or is not (locale_t) 0 and is not a valid locale object handle, the behavior is undefined.

The category_mask argument is a bit mask that specifies the locale categories that are to be set in a newly created locale object or modified in an existing object. The mask is constructed by a bitwise OR of the constants LC_ADDRESS_MASK, LC_CTYPE_MASK, LC_COLLATE_MASK, LC_IDENTIFICATION_MASK, LC_MEASUREMENT_MASK, LC_MESSAGES_MASK, LC_MONETARY_MASK, LC_NUMERIC_MASK, LC_NAME_MASK, LC_PAPER_MASK, LC_TELEPHONE_MASK, and LC_TIME_MASK. Alternatively, the mask can be specified as LC_ALL_MASK, which is equivalent to ORing all of the preceding constants.

For each category specified in category_mask, the locale data from locale will be used in the object returned by newlocale(). If a new locale object is being created, data for all categories not specified in category_mask is taken from the default ("POSIX") locale.

The following preset values of locale are defined for all categories that can be specified in category_mask:

"POSIX"

A minimal locale environment for C language programs.

"C"

Equivalent to "POSIX".

""

An implementation-defined native environment corresponding to the values of the LC_* and LANG environment variables (see locale(7)).

freelocale()

The freelocale() function deallocates the resources associated with locobj, a locale object previously returned by a call to newlocale() or duplocale(3). If locobj is LC_GLOBAL_LOCALE or is not valid locale object handle, the results are undefined.

Once a locale object has been freed, the program should make no further use of it.

On success, newlocale() returns a handle that can be used in calls to duplocale(3), freelocale(), and other functions that take a locale_t argument. On error, newlocale() returns (locale_t) 0, and sets errno to indicate the error.

The program below takes up to two command-line arguments, which each identify locales. The first argument is required, and is used to set the LC_NUMERIC category in a locale object created using newlocale(). The second command-line argument is optional; if it is present, it is used to set the LC_TIME category of the locale object.

Having created and initialized the locale object, the program then applies it using uselocale(3), and then tests the effect of the locale changes by:

1. Displaying a floating-point number with a fractional part. This output will be affected by the LC_NUMERIC setting. In many European-language locales, the fractional part of the number is separated from the integer part using a comma, rather than a period.

2. Displaying the date. The format and language of the output will be affected by the LC_TIME setting.

The following shell sessions show some example runs of this program.

Set the LC_NUMERIC category to fr_FR (French):

$ ./a.out fr_FR
123456,789
Fri Mar  7 00:25:08 2014

Set the LC_NUMERIC category to fr_FR (French), and the LC_TIME category to it_IT (Italian):

$ ./a.out fr_FR it_IT
123456,789
ven 07 mar 2014 00:26:01 CET

Specify the LC_TIME setting as an empty string, which causes the value to be taken from environment variable settings (which, here, specify mi_NZ, New Zealand Māori):

$ LC_ALL=mi_NZ ./a.out fr_FR ""
123456,789
Te Paraire, te 07 o Poutū-te-rangi, 2014 00:38:44 CET

Program source

#define _XOPEN_SOURCE 700
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                        } while (0)
int
main(int argc, char *argv[])
{
    char buf[100];
    time_t t;
    size_t s;
    struct tm *tm;
    locale_t loc, nloc;
    if (argc < 2) {
        fprintf(stderr, "Usage: %s locale1 [locale2]\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    /* Create a new locale object, taking the LC_NUMERIC settings
       from the locale specified in argv[1]. */
    loc = newlocale(LC_NUMERIC_MASK, argv[1], (locale_t) 0);
    if (loc == (locale_t) 0)
        errExit("newlocale");
    /* If a second command-line argument was specified, modify the
       locale object to take the LC_TIME settings from the locale
       specified in argv[2]. We assign the result of this newlocale()
       call to 'nloc' rather than 'loc', since in some cases, we might
       want to preserve 'loc' if this call fails. */
    if (argc > 2) {
        nloc = newlocale(LC_TIME_MASK, argv[2], loc);
        if (nloc == (locale_t) 0)
            errExit("newlocale");
        loc = nloc;
    }
    /* Apply the newly created locale to this thread. */
    uselocale(loc);
    /* Test effect of LC_NUMERIC. */
    printf("%8.3f\n", 123456.789);
    /* Test effect of LC_TIME. */
    t = time(NULL);
    tm = localtime(&t);
    if (tm == NULL)
        errExit("time");
    s = strftime(buf, sizeof(buf), "%c", tm);
    if (s == 0)
        errExit("strftime");
    printf("%s\n", buf);
    /* Free the locale object. */
    uselocale(LC_GLOBAL_LOCALE);    /* So 'loc' is no longer in use */
    freelocale(loc);
    exit(EXIT_SUCCESS);
}

locale(1), duplocale(3), setlocale(3), uselocale(3), locale(5), locale(7)