publish(3)

💅 publish(3) 💅

hey bestie 🫶 welcome to the Library Functions Manual, the part of your terminal where the C library pulls up and says "let me show you something." this page is literally one (1) entry, and it is not an options buffet — it's a whole entire working example program. no flags. no arguments. just code. and honestly? iconic. 💖

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✨ NAME ✨

publish — Publication example

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okay so, no cap, this is what you get: the example starts with its includes, its platform guards, and a lil stack of #defines, then it walks you through every callback a publishing client needs, and then main() ties the whole bow 🎀. read it top to bottom, it's giving tutorial energy.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "MQTTAsync.h"

#if !defined(_WIN32)
#include <unistd.h>
#else
#include <windows.h>
#endif

#if defined(_WRS_KERNEL)
#include <OsWrapper.h>
#endif

#define ADDRESS     "tcp://test.mosquitto.org:1883"
#define CLIENTID    "ExampleClientPub"
#define TOPIC       "MQTT Examples"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L

int finished = 0;

void connlost(void *context, char *cause)
{
        MQTTAsync client = (MQTTAsync)context;
        MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
        int rc;

        printf("\nConnection lost\n");
        printf("     cause: %s\n", cause);

        printf("Reconnecting\n");
        conn_opts.keepAliveInterval = 20;
        conn_opts.cleansession = 1;
        if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start connect, return code %d\n", rc);
                finished = 1;
        }
}

void onDisconnectFailure(void* context, MQTTAsync_failureData* response)
{
        printf("Disconnect failed\n");
        finished = 1;
}

void onDisconnect(void* context, MQTTAsync_successData* response)
{
        printf("Successful disconnection\n");
        finished = 1;
}

void onSendFailure(void* context, MQTTAsync_failureData* response)
{
        MQTTAsync client = (MQTTAsync)context;
        MQTTAsync_disconnectOptions opts = MQTTAsync_disconnectOptions_initializer;
        int rc;

        printf("Message send failed token %d error code %d\n", response->token, response->code);
        opts.onSuccess = onDisconnect;
        opts.onFailure = onDisconnectFailure;
        opts.context = client;
        if ((rc = MQTTAsync_disconnect(client, &opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start disconnect, return code %d\n", rc);
                exit(EXIT_FAILURE);
        }
}

void onSend(void* context, MQTTAsync_successData* response)
{
        MQTTAsync client = (MQTTAsync)context;
        MQTTAsync_disconnectOptions opts = MQTTAsync_disconnectOptions_initializer;
        int rc;

        printf("Message with token value %d delivery confirmed\n", response->token);
        opts.onSuccess = onDisconnect;
        opts.onFailure = onDisconnectFailure;
        opts.context = client;
        if ((rc = MQTTAsync_disconnect(client, &opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start disconnect, return code %d\n", rc);
                exit(EXIT_FAILURE);
        }
}

void onConnectFailure(void* context, MQTTAsync_failureData* response)
{
        printf("Connect failed, rc %d\n", response ? response->code : 0);
        finished = 1;
}

void onConnect(void* context, MQTTAsync_successData* response)
{
        MQTTAsync client = (MQTTAsync)context;
        MQTTAsync_responseOptions opts = MQTTAsync_responseOptions_initializer;
        MQTTAsync_message pubmsg = MQTTAsync_message_initializer;
        int rc;

        printf("Successful connection\n");
        opts.onSuccess = onSend;
        opts.onFailure = onSendFailure;
        opts.context = client;
        pubmsg.payload = PAYLOAD;
        pubmsg.payloadlen = (int)strlen(PAYLOAD);
        pubmsg.qos = QOS;
        pubmsg.retained = 0;
        if ((rc = MQTTAsync_sendMessage(client, TOPIC, &pubmsg, &opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start sendMessage, return code %d\n", rc);
                exit(EXIT_FAILURE);
        }
}

int messageArrived(void* context, char* topicName, int topicLen, MQTTAsync_message* m)
{
        // not expecting any messages
        return 1;
}

int main(int argc, char* argv[])
{
        MQTTAsync client;
        MQTTAsync_connectOptions conn_opts = MQTTAsync_connectOptions_initializer;
        int rc;

        if ((rc = MQTTAsync_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to create client object, return code %d\n", rc);
                exit(EXIT_FAILURE);
        }

        if ((rc = MQTTAsync_setCallbacks(client, NULL, connlost, messageArrived, NULL)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to set callback, return code %d\n", rc);
                exit(EXIT_FAILURE);
        }

        conn_opts.keepAliveInterval = 20;
        conn_opts.cleansession = 1;
        conn_opts.onSuccess = onConnect;
        conn_opts.onFailure = onConnectFailure;
        conn_opts.context = client;
        if ((rc = MQTTAsync_connect(client, &conn_opts)) != MQTTASYNC_SUCCESS)
        {
                printf("Failed to start connect, return code %d\n", rc);
                exit(EXIT_FAILURE);
        }

        printf("Waiting for publication of %s\n"
         "on topic %s for client with ClientID: %s\n",
         PAYLOAD, TOPIC, CLIENTID);
        while (!finished)
                #if defined(_WIN32)
                        Sleep(100);
                #else
                        usleep(10000L);
                #endif

        MQTTAsync_destroy(&client);
        return rc;
}

bestie note 🙈 — that's the whole page. every callback, every #define, every printf, every single brace, all of it, exactly as written. nothing skipped, nothing summarised. periodt. 💅

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and that's a wrap on publish(3), bestie 🌸 this lil legend lives in the Paho Asynchronous MQTT C... corner of the world, and it was dated Tue Jun 2 2026 00:00:00. go forth and publish, you absolute main character 👑✨🦋