getch

/*
 * Scans one character and returns it.
 * This method is multi-byte character sensitive.
 * See also #get_byte.
 *
 *   s = StringScanner.new('ab')
 *   s.getch           # => "a"
 *   s.getch           # => "b"
 *   s.getch           # => nil
 *
 *   $KCODE = 'EUC'
 *   s = StringScanner.new("\244\242")
 *   s.getch           # => "\244\242"   # Japanese hira-kana "A" in EUC-JP
 *   s.getch           # => nil
 */
static VALUE
strscan_getch(VALUE self)
{
    struct strscanner *p;
    long len;

    GET_SCANNER(self, p);
    CLEAR_MATCH_STATUS(p);
    if (EOS_P(p))
        return Qnil;
    len = mbclen(*CURPTR(p));
    if (p->curr + len > S_LEN(p)) {
        len = S_LEN(p) - p->curr;
    }
    p->prev = p->curr;
    p->curr += len;
    MATCHED(p);
    adjust_registers_to_matched(p);
    return extract_range(p, p->prev + p->regs.beg[0],
                            p->prev + p->regs.end[0]);
}