|  | Paho MQTT C Client Library
    | 
#include <MQTTClient.h>
| Data Fields | |
| char | struct_id [4] | 
| int | struct_version | 
| int | payloadlen | 
| void * | payload | 
| int | qos | 
| int | retained | 
| int | dup | 
| int | msgid | 
| MQTTProperties | properties | 
A structure representing the payload and attributes of an MQTT message. The message topic is not part of this structure (see MQTTClient_publishMessage(), MQTTClient_publish(), MQTTClient_receive(), MQTTClient_freeMessage() and MQTTClient_messageArrived()).
| char struct_id[4] | 
The eyecatcher for this structure. must be MQTM.
| int struct_version | 
The version number of this structure. Must be 0 or 1 0 indicates no message properties
| int payloadlen | 
The length of the MQTT message payload in bytes.
| void* payload | 
A pointer to the payload of the MQTT message.
| int qos | 
The quality of service (QoS) assigned to the message. There are three levels of QoS:
| int retained | 
The retained flag serves two purposes depending on whether the message it is associated with is being published or received.
retained = true
 For messages being published, a true setting indicates that the MQTT server should retain a copy of the message. The message will then be transmitted to new subscribers to a topic that matches the message topic. For subscribers registering a new subscription, the flag being true indicates that the received message is not a new one, but one that has been retained by the MQTT server.
retained = false 
 For publishers, this indicates that this message should not be retained by the MQTT server. For subscribers, a false setting indicates this is a normal message, received as a result of it being published to the server. 
| int dup | 
The dup flag indicates whether or not this message is a duplicate. It is only meaningful when receiving QoS1 messages. When true, the client application should take appropriate action to deal with the duplicate message.
| int msgid | 
The message identifier is normally reserved for internal use by the MQTT client and server.
| MQTTProperties properties | 
The MQTT V5 properties associated with the message.
 1.8.17
 1.8.17