check_until

/*
 * call-seq: check_until(pattern)
 *
 * This returns the value that #scan_until would return, without advancing the
 * scan pointer.  The match register is affected, though.
 *
 *   s = StringScanner.new("Fri Dec 12 1975 14:39")
 *   s.check_until /12/          # -> "Fri Dec 12"
 *   s.pos                       # -> 0
 *   s.matched                   # -> 12
 *
 * Mnemonic: it "checks" to see whether a #scan_until will return a value.
 */
static VALUE
strscan_check_until(VALUE self, VALUE re)
{
    return strscan_do_scan(self, re, 0, 1, 0);
}