rd_kafka_producev() var-arg example

producev.c

/*!
 * Partition (int32_t)
 */
#define RD_KAFKA_V_PARTITION(partition)                                 \
        _LRK_TYPECHECK(RD_KAFKA_VTYPE_PARTITION, int32_t, partition),   \
        (int32_t)partition
/*!
 * Message value/payload pointer and length (void *, size_t)
 */
#define RD_KAFKA_V_VALUE(VALUE,LEN)                                     \
        _LRK_TYPECHECK2(RD_KAFKA_VTYPE_VALUE, void *, VALUE, size_t, LEN), \
        (void *)VALUE, (size_t)LEN

...

err = rd_kafka_producev(rk,
          RD_KAFKA_V_TOPIC(topic),
          RD_KAFKA_V_VALUE(buf, sizeof(buf)),
          RD_KAFKA_V_KEY(key, sizeof(key)),
          RD_KAFKA_V_TIMESTAMP(my_timestamp.min),
          RD_KAFKA_V_MSGFLAGS(RD_KAFKA_MSG_F_COPY),
          RD_KAFKA_V_OPAQUE(&msgcounter),
          RD_KAFKA_V_END);