linux下用c实现传送json数据至mosquitto服务器

要在Linux下使用C语言将JSON数据传输到Mosquitto服务器，需要使用MQTT协议进行通信。下面是简单的步骤：

1. 安装Mosquitto客户端库

在Linux终端中运行以下命令安装Mosquitto客户端库：

sudo apt-get install libmosquitto-dev

2. 编写C程序

使用Mosquitto客户端库编写C程序。以下是示例代码：

#include <stdio.h>
#include <mosquitto.h>
#include <json-c/json.h>

void on_connect(struct mosquitto *mosq, void *obj, int rc)
{
    printf("Connected to Mosquitto\n");
}

void on_publish(struct mosquitto *mosq, void *obj, int mid)
{
    printf("Message %d sent to Mosquitto\n", mid);
}

int main()
{
    struct mosquitto *mosq = NULL;
    const char *topic = "test";
    int qos = 0;
    const char *host = "localhost";
    int port = 1883;
    const char *payload_str = "{\"name\":\"John\", \"age\":30, \"city\":\"New York\"}";
    struct json_object *payload = json_tokener_parse(payload_str);
    const char *payload_formatted = json_object_to_json_string(payload);

    mosquitto_lib_init();

    mosq = mosquitto_new(NULL, true, NULL);
    if (!mosq) {
        fprintf(stderr, "Error: Out of memory.\n");
        return 1;
    }

    mosquitto_connect_callback_set(mosq, on_connect);
    mosquitto_publish_callback_set(mosq, on_publish);

    if (mosquitto_connect(mosq, host, port, 60) != MOSQ_ERR_SUCCESS) {
        fprintf(stderr, "Error: Could not connect to Mosquitto.\n");
        mosquitto_disconnect(mosq);
        mosquitto_destroy(mosq);
        mosquitto_lib_cleanup();
        return 1;
    }

    if (mosquitto_publish(mosq, NULL, topic, strlen(payload_formatted), payload_formatted, qos, false) != MOSQ_ERR_SUCCESS) {
        fprintf(stderr, "Error: Could not publish message to Mosquitto.\n");
        mosquitto_disconnect(mosq);
        mosquitto_destroy(mosq);
        mosquitto_lib_cleanup();
        return 1;
    }

    mosquitto_disconnect(mosq);
    mosquitto_destroy(mosq);
    mosquitto_lib_cleanup();
    return 0;
}

3. 编译程序

在终端中运行以下命令编译程序：

gcc -o program program.c -lmosquitto -ljson-c

4. 运行程序

在终端中运行以下命令运行程序：

./program

程序将连接到Mosquitto服务器，并将JSON数据发布到指定的主题。

请注意，以上示例代码仅用于演示目的，实际使用时需要根据实际情况进行修改和调整。