/*
 * call-seq:
 *   strio.truncate(integer)    -> 0
 *
 * Truncates the buffer string to at most _integer_ bytes. The *strio*
 * must be opened for writing.
 */
static VALUE
strio_truncate(self, len)
    VALUE self, len;
{
    VALUE string = writable(StringIO(self))->string;
    long l = NUM2LONG(len);
    long plen = RSTRING(string)->len;
    if (l < 0) {
        error_inval("negative legnth");
    }
    rb_str_resize(string, l);
    if (plen < l) {
        MEMZERO(RSTRING(string)->ptr + plen, char, l - plen);
    }
    return len;
}