[Java知识库]EMQx 基于Eclipse Paho C 实现客户端与服务端的通信

概述

Eclipse Paho C (opens new window)与 Eclipse Paho Embedded C 均为 Eclipse Paho 项目下的 C 语言客户端库（MQTT C Client），均为使用 ANSI C 编写的功能齐全的 MQTT 客户端。

下载编译库文件

Linux/Mac

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

Windows

mkdir build.paho

cd build.paho

call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x64

cmake -G "NMake Makefiles" -DPAHO_WITH_SSL=TRUE -DPAHO_BUILD_DOCUMENTATION=FALSE -DPAHO_BUILD_SAMPLES=TRUE -DCMAKE_BUILD_TYPE=Release -DCMAKE_VERBOSE_MAKEFILE=TRUE ..
nmake

自行编译库文件，然后并对库文件进行安装

完整代码实现如下：

#include "stdlib.h"
#include "string.h"
#include "unistd.h"
#include "MQTTClient.h"

#define ADDRESS     "tcp://34.25.35.21:1883"
#define USERNAME    "emqx"
#define PASSWORD    "public"
#define CLIENTID    "c-client"
#define QOS         0
#define TOPIC       "emqx/c-test"
#define TIMEOUT     10000L

void publish(MQTTClient client, char *topic, char *payload) {
    MQTTClient_message message = MQTTClient_message_initializer;
    message.payload = payload;
    message.payloadlen = strlen(payload);
    message.qos = QOS;
    message.retained = 0;
    MQTTClient_deliveryToken token;
    MQTTClient_publishMessage(client, topic, &message, &token);
    MQTTClient_waitForCompletion(client, token, TIMEOUT);
    printf("Send `%s` to topic `%s` \n", payload, TOPIC);
}

int on_message(void *context, char *topicName, int topicLen, MQTTClient_message *message) {
    char *payload = message->payload;
    printf("Received `%s` from `%s` topic \n", payload, topicName);
    MQTTClient_freeMessage(&message);
    MQTTClient_free(topicName);
    return 1;
}

int main(int argc, char *argv[]) {
    int rc;
    MQTTClient client;

    MQTTClient_create(&client, ADDRESS, CLIENTID, 0, NULL);
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    conn_opts.username = USERNAME;
    conn_opts.password = PASSWORD;
    MQTTClient_setCallbacks(client, NULL, NULL, on_message, NULL);
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) {
        printf("Failed to connect, return code %d\n", rc);
        exit(-1);
    } else {
        printf("Connected to MQTT Broker!\n");
    }
    // subscribe topic
    MQTTClient_subscribe(client, TOPIC, QOS);
    char payload[16];
    for (int i = 0; i < 100; i += 1) {
        // publish message to broker
        snprintf(payload, 16, "message-%d", i);
        publish(client, TOPIC, payload);
        sleep(1);
    }
    MQTTClient_disconnect(client, TIMEOUT);
    MQTTClient_destroy(&client);
    return rc;
}

使用命令编译源文件：

linux 下编译代码

gcc mqtt_c.c -std=c99  -o mqtt_c -L./linux_mqtt_c -lpaho-mqtt3c

执行结果如下：

创作打卡挑战赛

赢取流量/现金/CSDN周边激励大奖