duplocale(3)               Library Functions Manual               duplocale(3)

NAME
       duplocale - duplicate a locale object

LIBRARY
       Standard C library (libc, -lc)

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.

STANDARDS
       POSIX.1-2008.

HISTORY
       glibc 2.3.

NOTES
       Duplicating a locale can serve the following purposes:

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

       o  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 <locale.h>
       #include <stdio.h>
       #include <stdlib.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)

Linux man-pages 6.7               2023-10-31                      duplocale(3)