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)):
Since glibc 2.10:
Before glibc 2.10:

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.

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 converted 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 example of its use is the following:

$  ./a.out abc

#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));

freelocale(3), newlocale(3), setlocale(3), uselocale(3), locale(5), locale(7)
2019-03-06 Linux