fusl/src/locale/uselocale.c

#include "locale_impl.h"
#include "pthread_impl.h"
#include "libc.h"

locale_t __uselocale(locale_t new) {
  pthread_t self = __pthread_self();
  locale_t old = self->locale;
  locale_t global = &libc.global_locale;

  if (new)
    self->locale = new == LC_GLOBAL_LOCALE ? global : new;

  return old == global ? LC_GLOBAL_LOCALE : old;
}

weak_alias(__uselocale, uselocale);