windows c语言使用mqtt向mosquitto服务器推送json数据

在Windows平台下使用C语言向Mosquitto服务器推送JSON数据需要先安装MQTT C客户端库，比如使用Eclipse Paho C库。

下面是一个简单的代码示例，用于将JSON数据发布到Mosquitto服务器：

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

#define ADDRESS     "tcp://localhost:1883"
#define CLIENTID    "ExampleClientPub"
#define TOPIC       "test"
#define QOS         1
#define TIMEOUT     10000L

int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    cJSON *root = NULL;
    char *payload = NULL;
    int rc;

    MQTTClient_create(&client, ADDRESS, CLIENTID,
        MQTTCLIENT_PERSISTENCE_NONE, NULL);

    conn_opts.keepAliveInterval = 20;
    conn_opts.cleansession = 1;

    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %d\n", rc);
        exit(EXIT_FAILURE);
    }

    root = cJSON_CreateObject();
    cJSON_AddStringToObject(root, "name", "John");
    cJSON_AddStringToObject(root, "surname", "Doe");
    cJSON_AddNumberToObject(root, "age", 30);
    payload = cJSON_Print(root);

    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    pubmsg.payload = payload;
    pubmsg.payloadlen = strlen(payload);
    pubmsg.qos = QOS;
    pubmsg.retained = 0;

    MQTTClient_deliveryToken token;
    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), payload, TOPIC, CLIENTID);
    rc = MQTTClient_waitForCompletion(client, token, TIMEOUT);
    printf("Message with delivery token %d delivered\n", token);

    cJSON_Delete(root);
    free(payload);
    MQTTClient_disconnect(client, 10000);
    MQTTClient_destroy(&client);
    return rc;
}

这个例子使用了两个库：MQTT C客户端库和cJSON库。它首先创建了一个MQTT客户端实例，然后连接到Mosquitto服务器。接下来，它使用cJSON库创建一个JSON对象，将其转换为字符串，然后将其作为消息发布到Mosquitto服务器。最后，它断开了MQTT连接并销毁了客户端实例。

需要注意的是，在使用这个例子之前，需要先安装并配置Mosquitto服务器，并使用正确的地址、客户端ID、主题等参数来运行程序。