阿里云物联网平台的连接实现 C语言代码

阿里云物联网平台提供了多种设备连接方式，包括 MQTT、CoAP、HTTP 等协议，您可以根据自己的需求选择合适的协议进行连接。

以下是一个基于 MQTT 协议连接阿里云物联网平台的 C 语言示例代码：

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

#define ADDRESS     "tcp://yourproductkey.iot-as-mqtt.cn-shanghai.aliyuncs.com:1883"  // 阿里云物联网平台 MQTT 服务器地址
#define CLIENTID    "yourclientid|securemode=3,signmethod=hmacsha1|"
#define USERNAME    "yourdeviceid&yourproductkey"  // 设备身份标识符
#define PASSWORD    "yourdevicesecret"  // 设备身份凭证

#define TOPIC_SUB   "/yourproductkey/yourdevicename/user/get"  // 订阅主题
#define TOPIC_PUB   "/yourproductkey/yourdevicename/user/update"  // 发布主题
#define QOS         1   // 消息质量

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

    char *payloadptr = message->payload;
    for (int 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;
    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    MQTTClient_deliveryToken token;

    int rc;

    MQTTClient_create(&client, ADDRESS, CLIENTID, MQTTCLIENT_PERSISTENCE_NONE, NULL);
    conn_opts.username = USERNAME;
    conn_opts.password = PASSWORD;
    conn_opts.keepAliveInterval = 20;
    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("Connected to %s\n", ADDRESS);

    if ((rc = MQTTClient_subscribe(client, TOPIC_SUB, QOS)) != MQTTCLIENT_SUCCESS) {
        printf("Failed to subscribe, return code %d\n", rc);
        exit(EXIT_FAILURE);
    }

    printf("Subscribed to %s\n", TOPIC_SUB);

    pubmsg.payload = "Hello, World!";
    pubmsg.payloadlen = strlen(pubmsg.payload);
    pubmsg.qos = QOS;
    pubmsg.retained = 0;
    MQTTClient_publishMessage(client, TOPIC_PUB, &pubmsg, &token);
    printf("Waiting for publication of %s\n"
           "on topic %s for client with ClientID: %s\n",
           pubmsg.payload, TOPIC_PUB, CLIENTID);
    while (deliveredtoken != token) {
        usleep(10000L);  // 暂停 10 毫秒
    }

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

需要注意的是，以上代码中的 `yourproductkey`、`yourdevicename`、`yourdeviceid` 和 `yourdevicesecret` 都需要根据实际情况替换为您的物联网平台中对应的值。同时，为了保证连接的安全性，建议使用 HTTPS 传输协议，并使用 TLS 或 DTLS 加密传输数据。