source: azure_iot_hub/trunk/musl-1.1.18/src/stdio/fgetwc.c@ 389

#include "stdio_impl.h"
#include "locale_impl.h"
#include <wchar.h>
#include <errno.h>

static wint_t __fgetwc_unlocked_internal(FILE *f)
{
        mbstate_t st = { 0 };
        wchar_t wc;
        int c;
        unsigned char b;
        size_t l;

        /* Convert character from buffer if possible */
        if (f->rpos < f->rend) {
                l = mbrtowc(&wc, (void *)f->rpos, f->rend - f->rpos, &st);
                if (l+2 >= 2) {
                        f->rpos += l + !l; /* l==0 means 1 byte, null */
                        return wc;
                }
                if (l == -1) {
                        f->rpos++;
                        return WEOF;
                }
        } else l = -2;

        /* Convert character byte-by-byte */
        while (l == -2) {
                b = c = getc_unlocked(f);
                if (c < 0) {
                        if (!mbsinit(&st)) errno = EILSEQ;
                        return WEOF;
                }
                l = mbrtowc(&wc, (void *)&b, 1, &st);
                if (l == -1) return WEOF;
        }

        return wc;
}

wint_t __fgetwc_unlocked(FILE *f)
{
        locale_t *ploc = &CURRENT_LOCALE, loc = *ploc;
        if (f->mode <= 0) fwide(f, 1);
        *ploc = f->locale;
        wchar_t wc = __fgetwc_unlocked_internal(f);
        *ploc = loc;
        return wc;
}

wint_t fgetwc(FILE *f)
{
        wint_t c;
        FLOCK(f);
        c = __fgetwc_unlocked(f);
        FUNLOCK(f);
        return c;
}

weak_alias(__fgetwc_unlocked, fgetwc_unlocked);
weak_alias(__fgetwc_unlocked, getwc_unlocked);