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Linux 2.6 - man page for duplocale (linux section 3)

DUPLOCALE(3)						     Linux Programmer's Manual						      DUPLOCALE(3)

duplocale - duplicate a locale object
#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
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).
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.
ENOMEM Insufficient memory to create the duplicate locale object.
The duplocale() function first appeared in version 2.3 of the GNU C library.
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 con- verted into a usable locale object. See EXAMPLE, below. Each locale object created by duplocale() should be deallocated using freelocale(3).
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 exam- ple 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); }
freelocale(3), newlocale(3), setlocale(3), uselocale(3), locale(5), locale(7) Linux 2014-03-12 DUPLOCALE(3)