97 lines
3.0 KiB
Groff
97 lines
3.0 KiB
Groff
.TH "MQTTClient_message" 3 "Sat Aug 16 2025 14:15:23" "Paho MQTT C Client Library" \" -*- nroff -*-
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.ad l
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.nh
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.SH NAME
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MQTTClient_message
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.SH SYNOPSIS
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.br
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.PP
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.PP
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\fR#include <MQTTClient\&.h>\fP
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.SS "Data Fields"
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.in +1c
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.ti -1c
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.RI "char \fBstruct_id\fP [4]"
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.br
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.ti -1c
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.RI "int \fBstruct_version\fP"
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.br
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.ti -1c
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.RI "int \fBpayloadlen\fP"
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.br
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.ti -1c
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.RI "void * \fBpayload\fP"
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.br
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.ti -1c
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.RI "int \fBqos\fP"
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.br
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.ti -1c
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.RI "int \fBretained\fP"
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.br
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.ti -1c
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.RI "int \fBdup\fP"
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.br
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.ti -1c
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.RI "int \fBmsgid\fP"
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.br
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.ti -1c
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.RI "\fBMQTTProperties\fP \fBproperties\fP"
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.br
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.in -1c
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.SH "Detailed Description"
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.PP
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A structure representing the payload and attributes of an MQTT message\&. The message topic is not part of this structure (see \fBMQTTClient_publishMessage()\fP, \fBMQTTClient_publish()\fP, \fBMQTTClient_receive()\fP, \fBMQTTClient_freeMessage()\fP and \fBMQTTClient_messageArrived()\fP)\&.
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.SH "Field Documentation"
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.PP
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.SS "char struct_id[4]"
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The eyecatcher for this structure\&. must be MQTM\&.
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.SS "int struct_version"
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The version number of this structure\&. Must be 0 or 1 0 indicates no message properties
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.SS "int payloadlen"
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The length of the MQTT message payload in bytes\&.
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.SS "void* payload"
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A pointer to the payload of the MQTT message\&.
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.SS "int qos"
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The quality of service (QoS) assigned to the message\&. There are three levels of QoS:
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.PP
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.IP "\fB\fBQoS0\fP
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.IP "" 1c
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Fire and forget - the message may not be delivered
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.PP
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.IP "\fB\fBQoS1\fP
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.IP "" 1c
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At least once - the message will be delivered, but may be delivered more than once in some circumstances\&.
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.PP
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.IP "\fB\fBQoS2\fP
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.IP "" 1c
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Once and one only - the message will be delivered exactly once\&.
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.PP
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.SS "int retained"
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The retained flag serves two purposes depending on whether the message it is associated with is being published or received\&.
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.PP
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\fBretained = true\fP
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.br
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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\&.
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.PP
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\fBretained = false\fP
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.br
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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\&.
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.SS "int dup"
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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\&.
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.SS "int msgid"
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The message identifier is normally reserved for internal use by the MQTT client and server\&.
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.SS "\fBMQTTProperties\fP properties"
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The MQTT V5 properties associated with the message\&.
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.SH "Author"
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.PP
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Generated automatically by Doxygen for Paho MQTT C Client Library from the source code\&.
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