Function is_utf8_charset

src/system.h:188–199

Return true if the current charset is UTF-8. */

/* Return true if the current charset is UTF-8.  */
static inline bool
is_utf8_charset (void)
{
  static int is_utf8 = -1;
  if (is_utf8 == -1)
    {
      char32_t w;
      mbstate_t mbs; mbszero (&mbs);
      is_utf8 = mbrtoc32 (&w, "\xe2\x9f\xb8", 3, &mbs) == 3 && w == 0x27F8;
    }
  return is_utf8;
}

#include <locale.h>