用c语言实现MQTT协议通信华为云IOT

在C语言中实现MQTT协议通信华为云IOT可以使用MQTT C语言客户端库，以下是具体的实现步骤： 1. 首先需要在华为云IOT上创建设备并获取设备证书以及设备ID和物联网平台的服务地址。 2. 下载MQTT C语言客户端库，例如Eclipse Paho MQTT C库，该库可以在Linux、Windows和Mac OS等平台上使用。下载地址：https://github.com/eclipse/paho.mqtt.c 3. 在代码中引入相关头文件： ```c #include "MQTTClient.h" ``` 4. 创建MQTT客户端并初始化MQTT连接参数： ```c MQTTClient client; MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer; ``` 5. 设置连接参数，包括设备证书、设备ID、服务地址、连接超时时间等： ```c char* address = "ssl://XXXX.iot-mqtts.cn-north-4.myhuaweicloud.com:8883"; char* clientID = "XXXX"; char* username = "XXXX"; char* password = "XXXX"; char* root_ca = "XXXX.pem"; conn_opts.keepAliveInterval = 20; conn_opts.cleansession = 1; conn_opts.username = username; conn_opts.password = password; conn_opts.ssl = &ssl_opts; ``` 其中，`ssl://XXXX.iot-mqtts.cn-north-4.myhuaweicloud.com:8883`为华为云IOT物联网平台的服务地址，`clientID`为设备ID，`username`和`password`为设备证书的用户名和密码，`root_ca`为根证书。 6. 创建MQTT连接： ```c MQTTClient_create(&client, address, clientID, MQTTCLIENT_PERSISTENCE_NONE, NULL); if (MQTTClient_connect(client, &conn_opts) != MQTTCLIENT_SUCCESS) { printf("Failed to connect\n"); return -1; } ``` 7. 发布消息： ```c MQTTClient_message pubmsg = MQTTClient_message_initializer; pubmsg.payload = "Hello world!"; pubmsg.payloadlen = strlen("Hello world!"); pubmsg.qos = QOS; MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token); ``` 其中，`TOPIC`为MQTT主题，`QOS`为消息发布的质量等级。 8. 订阅主题： ```c MQTTClient_subscribe(client, TOPIC, QOS); ``` 9. 接收消息： ```c void messageArrived(void *context, char *topicName, int topicLen, MQTTClient_message *message) { printf("Message arrived\n"); printf(" topic: %s\n", topicName); printf(" message: "); fwrite(message->payload, 1, message->payloadlen, stdout); printf("\n"); MQTTClient_freeMessage(&message); MQTTClient_free(topicName); } ``` 10. 断开MQTT连接： ```c MQTTClient_disconnect(client, 10000); MQTTClient_destroy(&client); ``` 完整的代码示例如下： ```c #include "MQTTClient.h" #include <string.h> #define QOS 1 #define TIMEOUT 10000L void messageArrived(void *context, char *topicName, int topicLen, MQTTClient_message *message) { printf("Message arrived\n"); printf(" topic: %s\n", topicName); printf(" message: "); fwrite(message->payload, 1, message->payloadlen, stdout); printf("\n"); MQTTClient_freeMessage(&message); MQTTClient_free(topicName); } int main(int argc, char* argv[]) { MQTTClient client; MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer; MQTTClient_SSLOptions ssl_opts = MQTTClient_SSLOptions_initializer; char* address = "ssl://XXXX.iot-mqtts.cn-north-4.myhuaweicloud.com:8883"; char* clientID = "XXXX"; char* username = "XXXX"; char* password = "XXXX"; char* root_ca = "XXXX.pem"; char* topic = "XXXX"; MQTTClient_message pubmsg = MQTTClient_message_initializer; MQTTClient_deliveryToken token; int rc; MQTTClient_create(&client, address, clientID, MQTTCLIENT_PERSISTENCE_NONE, NULL); conn_opts.keepAliveInterval = 20; conn_opts.cleansession = 1; conn_opts.username = username; conn_opts.password = password; ssl_opts.enableServerCertAuth = 1; ssl_opts.trustStore = root_ca; conn_opts.ssl = &ssl_opts; if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS) { printf("Failed to connect, return code %d\n", rc); return -1; } MQTTClient_subscribe(client, topic, QOS); MQTTClient_setCallbacks(client, NULL, NULL, messageArrived, NULL); pubmsg.payload = "Hello world!"; pubmsg.payloadlen = strlen("Hello world!"); pubmsg.qos = QOS; pubmsg.retained = 0; MQTTClient_publishMessage(client, topic, &pubmsg, &token); printf("Waiting for up to %d seconds for publication of %s\n" "on topic %s for client with ClientID: %s\n", (int)(TIMEOUT/1000), "Hello world!", topic, clientID); rc = MQTTClient_waitForCompletion(client, token, TIMEOUT); printf("Message with delivery token %d delivered\n", token); MQTTClient_disconnect(client, 10000); MQTTClient_destroy(&client); return rc; } ``` 注意，在使用该代码前需要将其中的`XXXX`替换为对应的设备证书、设备ID和华为云IOT服务地址等信息。