DUPLOCALE(3)

NAME
duplocale - duplicate a locale object

SYNOPSIS
#include <locale.h>
locale_t duplocale(locale_t locobj);

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

duplocale():
    Since glibc 2.10:
        _XOPEN_SOURCE >= 700
    Before glibc 2.10:
        _GNU_SOURCE

DESCRIPTION
The duplocale() function creates a duplicate of the locale object referred to by locobj. If locobj is LC_GLOBAL_LOCALE, duplocale() creates a locale object containing a copy of the global locale determined by setlocale(3).

RETURN VALUE
On success, duplocale() returns a handle for the new locale object. On error, it returns (locale_t) 0, and sets errno to indicate the cause of the error.

ERRORS

ENOMEM
    Insufficient memory to create the duplicate locale object.

VERSIONS
The duplocale() function first appeared in version 2.3 of the GNU C library.

CONFORMING TO
POSIX.1-2008.

NOTES
Duplicating a locale can serve the following purposes:

*   To create a copy of a locale object in which one of more categories are to be modified (using newlocale(3)).

*   To obtain a handle for the current locale which can used in other functions that employ a locale handle, such as toupper_l(3). This is done by applying duplocale() to the value returned by the following call:
        loc = uselocale((locale_t) 0);

    This technique is necessary, because the above uselocale(3) call may return the value LC_GLOBAL_LOCALE, which results in undefined behavior if passed to functions such as toupper_l(3). Calling duplocale() can be used to ensure that the LC_GLOBAL_LOCALE value is converted into a usable locale object. See EXAMPLE, below.

Each locale object created by duplocale() should be deallocated using freelocale(3).

EXAMPLE
The program below uses uselocale(3) and duplocale() to obtain a handle for the current locale which is then passed to toupper_l(3). The program takes one command-line argument, a string of characters that is converted to uppercase and displayed on standard output. An example of its use is the following:
$ ./a.out abc
ABC

  Program source
#define _XOPEN_SOURCE 700
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <locale.h>
#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
                        } while (0)
int
main(int argc, char *argv[])
{
    locale_t loc, nloc;
    char *p;
    if (argc != 2) {
        fprintf(stderr, "Usage: %s string\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    /* This sequence is necessary, because uselocale() might return
       the value LC_GLOBAL_LOCALE, which can't be passed as an
       argument to toupper_l() */
    loc = uselocale((locale_t) 0);
    if (loc == (locale_t) 0)
        errExit("uselocale");
    nloc = duplocale(loc);
    if (nloc == (locale_t) 0)
        errExit("duplocale");
    for (p = argv[1]; *p; p++)
        putchar(toupper_l(*p, nloc));
    printf("\n");
    freelocale(nloc);
    exit(EXIT_SUCCESS);
}

SEE ALSO
freelocale(3), newlocale(3), setlocale(3), uselocale(3), locale(5), locale(7)

COLOPHON
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