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 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

       This  page  is  part  of  release  5.10  of  the  Linux man-pages project.  A description of the project,
       information  about  reporting  bugs,  and  the  latest  version  of  this   page,   can   be   found   at
       https://www.kernel.org/doc/man-pages/.

Linux                                              2020-11-01                                       DUPLOCALE(3)