官網(wǎng)：http://www.eclipse.org/paho/clients/c/

編譯流程：

git clone https://github.com/eclipse/paho.mqtt.c.git cd org.eclipse.paho.mqtt.c.git make sudo make install

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編譯過(guò)程中報(bào)找不到clock_gettime函數(shù)的錯(cuò)誤，在Makefile中相關(guān)位置添加-lrt就可以了。

make后sample里的測(cè)試代碼也會(huì)跟著成功編譯。

也可以在sample目錄下單獨(dú)用命令編譯：gcc -I../ -L../../../paho.mqtt.c/build/output/ MQTTClient_subscribe.c -lpaho-mqtt3c -o MQTTTest -lrt

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我測(cè)試了訂閱部分，修改了原版demo，同時(shí)和服務(wù)器建立4個(gè)連接，每個(gè)連接又訂閱了4個(gè)主題。通過(guò)對(duì)主題進(jìn)行數(shù)據(jù)發(fā)送和抓包分析，都顯示沒(méi)問(wèn)題。

修改后的代碼如下：

/*******************************************************************************
?* Copyright (c) 2012, 2017 IBM Corp.
?*
?* All rights reserved. This program and the accompanying materials
?* are made available under the terms of the Eclipse Public License v1.0
?* and Eclipse Distribution License v1.0 which accompany this distribution.?
?*
?* The Eclipse Public License is available at?
?* ? http://www.eclipse.org/legal/epl-v10.html
?* and the Eclipse Distribution License is available at?
?* ? http://www.eclipse.org/org/documents/edl-v10.php.
?*
?* Contributors:
?* ? ?Ian Craggs - initial contribution
?*******************************************************************************/

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

//#define ADDRESS ? ? "tcp://localhost:1883"
//#define ADDRESS ? ? "192.168.0.167"
#define ADDRESS ? ? "192.168.0.117"
#define CLIENTID ? ?"ExampleClientSub"
#define TOPIC ? ? ? "1234/qinrenzhi"
#define TOPIC_11 ? ?"1234/qinrenzhi_11"
#define TOPIC_12 ? ?"1234/qinrenzhi_12"
#define TOPIC_13 ? ?"1234/qinrenzhi_13"
#define TOPIC_14 ? ?"1234/qinrenzhi_14"

#define PAYLOAD ? ? "Hello World!"
#define QOS ? ? ? ? 1
#define TIMEOUT ? ? 10000L

#define CLIENTID_2 ? ?"ExampleClientSub_2"
#define TOPIC_2 ? ? ? "1234/qinrenzhi_2"
#define TOPIC_21 ? ? ?"1234/qinrenzhi_21"
#define TOPIC_22 ? ? ?"1234/qinrenzhi_22"
#define TOPIC_23 ? ? ?"1234/qinrenzhi_23"

#define CLIENTID_3 ? ?"ExampleClientSub_3"
#define TOPIC_3 ? ? ? "1234/qinrenzhi_3"
#define TOPIC_31 ? ? ? "1234/qinrenzhi_31"
#define TOPIC_32 ? ? ? "1234/qinrenzhi_32"
#define TOPIC_33 ? ? ? "1234/qinrenzhi_33"

#define CLIENTID_4 ? ?"ExampleClientSub_4"
#define TOPIC_4 ? ? ? "1234/qinrenzhi_4"
#define TOPIC_41 ? ? ?"1234/qinrenzhi_41"
#define TOPIC_42 ? ? ?"1234/qinrenzhi_42"
#define TOPIC_43 ? ? ?"1234/qinrenzhi_43"

volatile MQTTClient_deliveryToken deliveredtoken_2;

void delivered_2(void *context, MQTTClient_deliveryToken dt)
{
? ? printf("2:Message with token value %d delivery confirmed\n", dt);
? ? deliveredtoken_2 = dt;
}

int msgarrvd_2(void *context, char *topicName, int topicLen, MQTTClient_message *message)
{
? ? int i;
? ? char* payloadptr;

? ? printf("2:Message arrived\n");
? ? printf("2: ? ? topic: %s\n", topicName);
? ? printf("2: ? message: ");

? ? payloadptr = message->payload;
? ? for(i=0; i<message->payloadlen; i++)
? ? {
? ? ? ? putchar(*payloadptr++);
? ? }
? ? putchar('\n');
? ? MQTTClient_freeMessage(&message);
? ? MQTTClient_free(topicName);
? ? return 1;
}

void connlost_2(void *context, char *cause)
{
? ? printf("\n2:Connection lost\n");
? ? printf(" ? ? cause: %s\n", cause);
}

volatile MQTTClient_deliveryToken deliveredtoken_3;

void delivered_3(void *context, MQTTClient_deliveryToken dt)
{
? ? printf("3:Message with token value %d delivery confirmed\n", dt);
? ? deliveredtoken_3 = dt;
}

int msgarrvd_3(void *context, char *topicName, int topicLen, MQTTClient_message *message)
{
? ? int i;
? ? char* payloadptr;

? ? printf("3:Message arrived\n");
? ? printf("3: ? ? topic: %s\n", topicName);
? ? printf("3: ? message: ");

? ? payloadptr = message->payload;
? ? for(i=0; i<message->payloadlen; i++)
? ? {
? ? ? ? putchar(*payloadptr++);
? ? }
? ? putchar('\n');
? ? MQTTClient_freeMessage(&message);
? ? MQTTClient_free(topicName);
? ? return 1;
}

void connlost_3(void *context, char *cause)
{
? ? printf("\n3:Connection lost\n");
? ? printf(" ? ? cause: %s\n", cause);
}

volatile MQTTClient_deliveryToken deliveredtoken_4;

void delivered_4(void *context, MQTTClient_deliveryToken dt)
{
? ? printf("4:Message with token value %d delivery confirmed\n", dt);
? ? deliveredtoken_4 = dt;
}

int msgarrvd_4(void *context, char *topicName, int topicLen, MQTTClient_message *message)
{
? ? int i;
? ? char* payloadptr;

? ? printf("4:Message arrived\n");
? ? printf("4: ? ? topic: %s\n", topicName);
? ? printf("4: ? message: ");

? ? payloadptr = message->payload;
? ? for(i=0; i<message->payloadlen; i++)
? ? {
? ? ? ? putchar(*payloadptr++);
? ? }
? ? putchar('\n');
? ? MQTTClient_freeMessage(&message);
? ? MQTTClient_free(topicName);
? ? return 1;
}

void connlost_4(void *context, char *cause)
{
? ? printf("\n4:Connection lost\n");
? ? printf(" ? ? cause: %s\n", cause);
}

volatile MQTTClient_deliveryToken deliveredtoken;

void delivered(void *context, MQTTClient_deliveryToken dt)
{
? ? printf("Message with token value %d delivery confirmed\n", dt);
? ? deliveredtoken = dt;
}

int msgarrvd(void *context, char *topicName, int topicLen, MQTTClient_message *message)
{
? ? int i;
? ? char* payloadptr;

? ? printf("Message arrived\n");
? ? printf(" ? ? topic: %s\n", topicName);
? ? printf(" ? message: ");

? ? payloadptr = message->payload;
? ? for(i=0; i<message->payloadlen; i++)
? ? {
? ? ? ? putchar(*payloadptr++);
? ? }
? ? putchar('\n');
? ? MQTTClient_freeMessage(&message);
? ? MQTTClient_free(topicName);
? ? return 1;
}

void connlost(void *context, char *cause)
{
? ? printf("\nConnection lost\n");
? ? printf(" ? ? cause: %s\n", cause);
}

int main(int argc, char* argv[])
{
? ? MQTTClient client;
? ? MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
? ? int rc;
? ? int ch;

? ? MQTTClient_create(&client, ADDRESS, CLIENTID,
? ? ? ? MQTTCLIENT_PERSISTENCE_NONE, NULL);
? ? conn_opts.keepAliveInterval = 200;
? ? conn_opts.cleansession = 1;

? ? MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered);

? ? if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
? ? {
? ? ? ? printf("Failed to connect, return code %d\n", rc);
? ? ? ? exit(EXIT_FAILURE);
? ? }
? ? printf("Subscribing to topic %s\nfor client %s using QoS%d\n\n"
? ? ? ? ? ?"Press Q<Enter> to quit\n\n", TOPIC, CLIENTID, QOS);
? ? MQTTClient_subscribe(client, TOPIC, QOS);
? ? MQTTClient_subscribe(client, TOPIC_11, QOS);
? ? MQTTClient_subscribe(client, TOPIC_12, QOS);
? ? MQTTClient_subscribe(client, TOPIC_13, QOS);

? ? MQTTClient client_2;
? ? MQTTClient_connectOptions conn_opts_2 = MQTTClient_connectOptions_initializer;
? ? int rc_2;
? ? int ch_2;

? ? MQTTClient_create(&client_2, ADDRESS, CLIENTID_2,
? ? ? ? MQTTCLIENT_PERSISTENCE_NONE, NULL);
? ? conn_opts_2.keepAliveInterval = 200;
? ? conn_opts_2.cleansession = 1;

? ? MQTTClient_setCallbacks(client_2, NULL, connlost_2, msgarrvd_2, delivered_2);

? ? if ((rc_2 = MQTTClient_connect(client_2, &conn_opts_2)) != MQTTCLIENT_SUCCESS)
? ? {
? ? ? ? printf("2:Failed to connect, return code %d\n", rc);
? ? ? ? exit(EXIT_FAILURE);
? ? }
? ? printf("2:Subscribing to topic %s\nfor client %s using QoS%d\n\n"
? ? ? ? ? ?"Press Q<Enter> to quit\n\n", TOPIC_2, CLIENTID_2, QOS);
? ? MQTTClient_subscribe(client_2, TOPIC_2, QOS);
? ? MQTTClient_subscribe(client_2, TOPIC_21, QOS);
? ? MQTTClient_subscribe(client_2, TOPIC_22, QOS);
? ? MQTTClient_subscribe(client_2, TOPIC_23, QOS);

? ? MQTTClient client_3;
? ? MQTTClient_connectOptions conn_opts_3 = MQTTClient_connectOptions_initializer;
? ? int rc_3;
? ? int ch_3;

? ? MQTTClient_create(&client_3, ADDRESS, CLIENTID_3,
? ? ? ? MQTTCLIENT_PERSISTENCE_NONE, NULL);
? ? conn_opts_3.keepAliveInterval = 200;
? ? conn_opts_3.cleansession = 1;

? ? MQTTClient_setCallbacks(client_3, NULL, connlost_3, msgarrvd_3, delivered_3);

? ? if ((rc_3 = MQTTClient_connect(client_3, &conn_opts_3)) != MQTTCLIENT_SUCCESS)
? ? {
? ? ? ? printf("3:Failed to connect, return code %d\n", rc);
? ? ? ? exit(EXIT_FAILURE);
? ? }
? ? printf("3:Subscribing to topic %s\nfor client %s using QoS%d\n\n"
? ? ? ? ? ?"Press Q<Enter> to quit\n\n", TOPIC_3, CLIENTID_3, QOS);
? ? MQTTClient_subscribe(client_3, TOPIC_3, QOS);
? ? MQTTClient_subscribe(client_3, TOPIC_31, QOS);
? ? MQTTClient_subscribe(client_3, TOPIC_32, QOS);
? ? MQTTClient_subscribe(client_3, TOPIC_33, QOS);

? ? MQTTClient client_4;
? ? MQTTClient_connectOptions conn_opts_4 = MQTTClient_connectOptions_initializer;
? ? int rc_4;
? ? int ch_4;

? ? MQTTClient_create(&client_4, ADDRESS, CLIENTID_4,
? ? ? ? MQTTCLIENT_PERSISTENCE_NONE, NULL);
? ? conn_opts_4.keepAliveInterval = 200;
? ? conn_opts_4.cleansession = 1;

? ? MQTTClient_setCallbacks(client_4, NULL, connlost_4, msgarrvd_4, delivered_4);

? ? if ((rc_4 = MQTTClient_connect(client_4, &conn_opts_4)) != MQTTCLIENT_SUCCESS)
? ? {
? ? ? ? printf("4:Failed to connect, return code %d\n", rc);
? ? ? ? exit(EXIT_FAILURE);
? ? }
? ? printf("4:Subscribing to topic %s\nfor client %s using QoS%d\n\n"
? ? ? ? ? ?"Press Q<Enter> to quit\n\n", TOPIC_4, CLIENTID_4, QOS);
? ? MQTTClient_subscribe(client_4, TOPIC_4, QOS);
? ? MQTTClient_subscribe(client_4, TOPIC_41, QOS);
? ? MQTTClient_subscribe(client_4, TOPIC_42, QOS);
? ? MQTTClient_subscribe(client_4, TOPIC_43, QOS);

? ? do?
? ? {
? ? ? ? ch = getchar();
? ? } while(ch!='Q' && ch != 'q');

? ? MQTTClient_unsubscribe(client, TOPIC);
? ? MQTTClient_unsubscribe(client, TOPIC_11);
? ? MQTTClient_unsubscribe(client, TOPIC_12);
? ? MQTTClient_unsubscribe(client, TOPIC_13);
? ? MQTTClient_disconnect(client, 10000);
? ? MQTTClient_destroy(&client);

? ? MQTTClient_unsubscribe(client_2, TOPIC);
? ? MQTTClient_unsubscribe(client_2, TOPIC_21);
? ? MQTTClient_unsubscribe(client_2, TOPIC_22);
? ? MQTTClient_unsubscribe(client_2, TOPIC_23);
? ? MQTTClient_disconnect(client_2, 10000);
? ? MQTTClient_destroy(&client_2);

? ? MQTTClient_unsubscribe(client_3, TOPIC);
? ? MQTTClient_unsubscribe(client_3, TOPIC_31);
? ? MQTTClient_unsubscribe(client_3, TOPIC_32);
? ? MQTTClient_unsubscribe(client_3, TOPIC_33); ?
? ? MQTTClient_disconnect(client_3, 10000);
? ? MQTTClient_destroy(&client_3);

? ? MQTTClient_unsubscribe(client_4, TOPIC);
? ? MQTTClient_unsubscribe(client_4, TOPIC_41);
? ? MQTTClient_unsubscribe(client_4, TOPIC_42);
? ? MQTTClient_unsubscribe(client_4, TOPIC_43);
? ? MQTTClient_disconnect(client_4, 10000);
? ? MQTTClient_destroy(&client_4);

? ? return rc;
}
?

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