mqtt上传字符串到onenet c语言

在C语言中使用MQTT上传字符串到OneNet平台，你可以使用MQTT客户端库来实现。以下是一个简单的示例代码：

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

#define ADDRESS     "tcp://mqtt.heclouds.com:1883"
#define CLIENTID    "client_id"
#define TOPIC       "topic"
#define QOS         1
#define TIMEOUT     10000L
#define USERNAME    "your_username"
#define PASSWORD    "your_password"

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: %s\n", message->payload);
    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;
    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;

    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(-1);
    }

    char* payload = "Hello, OneNet!";
    MQTTClient_message pubmsg = MQTTClient_message_initializer;
    MQTTClient_deliveryToken token;
    pubmsg.payload = payload;
    pubmsg.payloadlen = strlen(payload);
    pubmsg.qos = QOS;
    pubmsg.retained = 0;

    MQTTClient_publishMessage(client, TOPIC, &pubmsg, &token);
    printf("Waiting for publication of %s on topic %s for client with ClientID: %s\n",
        payload, 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;
}

请确保在使用此代码之前已安装MQTT C客户端库，并将代码中的`ADDRESS`、`CLIENTID`、`TOPIC`、`USERNAME`和`PASSWORD`替换为你的OneNet平台相关信息。此代码将连接到OneNet平台并发布一个字符串消息到指定的主题。

注意：此示例代码仅用于演示目的，实际使用时可能需要进行错误处理和其他优化。