linux下mqtt源码交叉编译和应用

1 、下载压缩包解压

paho.mqtt.c-master.zip
直接下载源码即可，根据自己想要的版本下载就好，一般选最新稳定版
下载链接：
github:https://github.com/eclipse/paho.mqtt.c/releases
gitee:https://gitee.com/IOTTS/paho.mqtt.c.git

2、编译linux下源码包直接在目录下执行make命令

生成动态库在 build/output/ 目录下，头文件目录 srt/目录下。可以将动态库和头文件一个拷贝出来，放在自己应用的源码里面可以直接使用。

3、嵌入式linux平台交叉编译

将Makefile中的gcc换成嵌入式交叉编译工具：(注意如果已经生成过bulid文件就不会继续执行makefile,需要删除以前的生成文件，或者直接将压缩包重新解压，直接修改makefile文件后执行make命令编译)
makefile将编译器换掉CC= arm-arago-linux-gnueabi-gcc

操作和步骤2相同，只是生产的文件是响应嵌入式linux平台的动态库

4、MQTT应用开发

Demo程序

#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "src/MQTTClient.h"   /* MQTT头文件的位置  */
#include <sys/time.h>   
#include <termios.h>
#include <iostream>

#define ADDRESS     "tcp://localhost:1883"   /* 指定服务器的ip地址 这里使用本机的 mosquitto 进行测试使用  */
#define CLIENTID    "ExampleClientPub"
#define TOPIC       "MQTT Examples"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L

using namespace std;
int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    MQTTClient_deliveryToken token;

    MQTTClient_message *receivemsg = NULL ;
    char* topicName_rev = NULL;
    int   topicLen_rev;

    int rc;
    int i;

    MQTTClient_create(&client, ADDRESS, CLIENTID,
        MQTTCLIENT_PERSISTENCE_NONE, NULL);
    conn_opts.keepAliveInterval = 60;
    conn_opts.cleansession = 1;

    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %d\n", rc);
        exit(-1);
    }
    pubmsg.payload = (void *)PAYLOAD;
    pubmsg.payloadlen = strlen(PAYLOAD);
    pubmsg.qos = QOS;
    pubmsg.retained = 0;
    MQTTClient_subscribe(client, "test", 1);                        /* 订阅一个客户端 的一个话题*/
    usleep(10000); 
    MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token); /* 发送消息 */
    printf("Waiting for up to %d seconds for publication of %s\n"
            "on topic %s for client with ClientID: %s\n",
            (int)(TIMEOUT/1000), PAYLOAD, TOPIC, CLIENTID);
    rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
    printf("Message with delivery token %d delivered\n", token);
    for(;;)
    {
               if(MQTTClient_isConnected(client) == true)   /* 检测连接状态 */
               {
                   printf("alive \n");
               }else{
                   printf(" no alive \n");
                   break;
               }
            rc = MQTTClient_receive(client,&topicName_rev, &topicLen_rev, &receivemsg,5000); /* 接收消息 */
               if(rc == MQTTCLIENT_SUCCESS)
               {
                printf("Message REv  %d delivered\n", rc);
                printf("topicName: %s  topicName_LEN: %d \n", topicName_rev,topicLen_rev);
                if(topicName_rev != NULL)                          /* 滤掉心跳包 */
                {
                    printf("topicName: ");
                    for(i=0;i<topicLen_rev;i++)
                    {
                        printf(" %c ", topicName_rev[i]);
                    }
                    printf("\n");
                    printf("Data: %s  len:%d msgid: %d \n",(char *)receivemsg->payload,receivemsg->payloadlen,receivemsg->msgid);
                     if(strcmp((char *)receivemsg->payload,"ESC") == 0)
                    {
                        printf("ESC \n");
                        break;
                    }
                }
            }

            usleep(10000); 
            usleep(100000);
    }
    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return rc;
}