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 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 EXAMPLES, below.

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

EXAMPLES
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;
        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 (char *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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