/** The class defining a handle to an Innodb table */
class ha_innobase: public handler
{
    row_prebuilt_t*    prebuilt;    /*!< prebuilt struct in InnoDB, used
                    to save CPU time with prebuilt data
                    structures*/
        。。。。。
}

ha_innobase::open
    prebuilt = row_create_prebuilt(ib_table, table->s->reclength);
        //成员变量赋值，跟php不一样,php的还需要$this