source: azure_iot_hub/trunk/musl-1.1.18/src/locale/setlocale.c@ 389

#include <locale.h>
#include <stdlib.h>
#include <string.h>
#include "locale_impl.h"
#include "libc.h"
#include "atomic.h"

static char buf[LC_ALL*(LOCALE_NAME_MAX+1)];

static char *setlocale_one_unlocked(int cat, const char *name)
{
        const struct __locale_map *lm;

        if (name) libc.global_locale.cat[cat] = lm = __get_locale(cat, name);
        else lm = libc.global_locale.cat[cat];

        return lm ? (char *)lm->name : "C";
}

char *__strchrnul(const char *, int);

char *setlocale(int cat, const char *name)
{
        static volatile int lock[2];

        if ((unsigned)cat > LC_ALL) return 0;

        LOCK(lock);

        /* For LC_ALL, setlocale is required to return a string which
         * encodes the current setting for all categories. The format of
         * this string is unspecified, and only the following code, which
         * performs both the serialization and deserialization, depends
         * on the format, so it can easily be changed if needed. */
        if (cat == LC_ALL) {
                int i;
                if (name) {
                        char part[LOCALE_NAME_MAX+1] = "C.UTF-8";
                        const char *p = name;
                        for (i=0; i<LC_ALL; i++) {
                                const char *z = __strchrnul(p, ';');
                                if (z-p <= LOCALE_NAME_MAX) {
                                        memcpy(part, p, z-p);
                                        part[z-p] = 0;
                                        if (*z) p = z+1;
                                }
                                setlocale_one_unlocked(i, part);
                        }
                }
                char *s = buf;
                const char *part;
                int same = 0;
                for (i=0; i<LC_ALL; i++) {
                        const struct __locale_map *lm =
                                libc.global_locale.cat[i];
                        if (lm == libc.global_locale.cat[0]) same++;
                        part = lm ? lm->name : "C";
                        size_t l = strlen(part);
                        memcpy(s, part, l);
                        s[l] = ';';
                        s += l+1;
                }
                *--s = 0;
                UNLOCK(lock);
                return same==LC_ALL ? (char *)part : buf;
        }

        char *ret = setlocale_one_unlocked(cat, name);

        UNLOCK(lock);

        return ret;
}