中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云-接收和发送数据)

B站：https://space.bilibili.com/309103931

中移4G模块-ML302专栏：https://blog.csdn.net/qq_33259323/category_10453372.html

中移4G模块-ML302文集：https://www.bilibili.com/read/readlist/rl328642

1.中移4G模块-ML302-OpenCpu开发-(固件编译和烧录)

https://blog.csdn.net/qq_33259323/article/details/108586847

https://www.bilibili.com/read/cv7876504

2.中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云)

https://blog.csdn.net/qq_33259323/article/details/108638945

https://www.bilibili.com/read/cv7876527

2.1中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云-订阅主题)

https://blog.csdn.net/qq_33259323/article/details/108960540

https://www.bilibili.com/read/cv7879954

2.2中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云-接收和发送数据)

https://blog.csdn.net/qq_33259323/article/details/108964810

https://www.bilibili.com/read/cv7886836

2.3中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云-RRPC通讯)

https://blog.csdn.net/qq_33259323/article/details/108965071

https://www.bilibili.com/read/cv7888259

3.中移4G模块-ML302-OpenCpu开发-串口开发

https://blog.csdn.net/qq_33259323/article/details/108974888

https://www.bilibili.com/read/cv7888865

4.中移4G模块-ML302-OpenCpu开发-51单片机串口转I2C

https://blog.csdn.net/qq_33259323/article/details/109020642

https://www.bilibili.com/read/cv7922942

5.中移4G模块-ML302-OpenCpu开发-MCP23017输入/输出

https://blog.csdn.net/qq_33259323/article/details/109109136

https://www.bilibili.com/read/cv7969395

7.中移4G模块-ML302-OpenCpu开发-PCF8591测量电压

https://blog.csdn.net/qq_33259323/article/details/109109266

https://www.bilibili.com/read/cv7969365

8.中移4G模块-ML302-OpenCpu开发-GPIO

https://blog.csdn.net/qq_33259323/article/details/108960947

https://www.bilibili.com/read/cv7877192

9.中移4G模块-ML302-OpenCpu开发-ADC

https://blog.csdn.net/qq_33259323/article/details/109020864

https://www.bilibili.com/read/cv7922958

10.中移4G模块-ML302-OpenCpu开发-CJSON

https://blog.csdn.net/qq_33259323/article/details/109020898

https://www.bilibili.com/read/cv7923020

11.中移4G模块-ML302-OpenCpu开发-HTTP

https://blog.csdn.net/qq_33259323/article/details/109020904

https://www.bilibili.com/read/cv7923054

根据上一条的学习，如果没看过可以去看一下上面的2.1中移4G模块-ML302-OpenCpu开发-(MQTT连接阿里云-订阅主题)

数据是可以接收了，那怎么发送呢。

int example_publish(void *handle)
{
    int             res = 0;
    const char     *fmt = "/%s/%s/user/get";
    char           *topic = NULL;
    int             topic_len = 0;
    char           *payload = "{"message":"hello!"}";

    //*** 对topic的拼接***

    topic_len = strlen(fmt) + strlen(DEMO_PRODUCT_KEY) + strlen(DEMO_DEVICE_NAME) + 1;
    topic = HAL_Malloc(topic_len);
    if (topic == NULL) {
        cm_printf("[ALIYUN]: memory not enough
");  
        return -1;
    }
    memset(topic, 0, topic_len);
    HAL_Snprintf(topic, topic_len, fmt, DEMO_PRODUCT_KEY, DEMO_DEVICE_NAME);

    //*** 对topic的拼接***
    
    // 调用IOT_MQTT_Publish_Simple发送数据
    res = IOT_MQTT_Publish_Simple(0, topic, IOTX_MQTT_QOS0, payload, strlen(payload));
    
    if (res < 0) {
        cm_printf("[ALIYUN]: publish failed, res = %d
", res);
        HAL_Free(topic);
        return -1;
    }

    HAL_Free(topic);
    return 0;
}

IOT_MQTT_Publish_Simple函数

topic_name：topic名字

qos:qos

data:数据

len:发送数据长度

int IOT_MQTT_Publish_Simple(void *handle, const char *topic_name, int qos, void *data, int len)

这是一个比较简单的MQTT发送程序