关于用邮箱传输变量数据的一些疑问

发布于 2023-02-26 20:33:28 浏览：614 订阅该版

我看站内有个关于邮箱传输变量数据的回答下，关于如何传输是这样的：

![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20230226/bb0597fab7898db9e4a70df8e4fb2236.png.webp)

![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20230226/fb3bf68549300ea1e4dd7679ef266c08.png)

![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20230226/af1928ca00600f1127d883b77854d389.png)

我的问题是为啥整这么复杂，查看rt_mb_send()函数可以看到第二个形参是rt_ubase_t类型的，追溯一下就是unsigned long类型的数。不懂为何看到的帖子里需要做强制类型转换，或者取地址的。
![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20230226/60dd77f660a5765b2459fea1305eab1a.png)

以下是我进行邮箱传输变量的代码：

```c

#include <rtthread.h>

rt_mailbox_t mail = RT_NULL;//创建邮箱指针变量
//创建线程指针变量
rt_thread_t th1 = RT_NULL;
rt_thread_t th2 = RT_NULL;

void thread1_entry(void *parameter)
{
    rt_ubase_t val = RT_NULL;
    while(1)
    {
        if(rt_mb_recv(mail, &val, RT_WAITING_FOREVER) == RT_EOK)
        {
            if(val == 0)
                rt_kprintf("action 1\n");
            if(val == 1)
                rt_kprintf("action 2\n");
            if(val == 2)
                rt_kprintf("action 3\n");
            if(val == 3)
                rt_kprintf("action 4\n");
            if(val == 4)
                rt_kprintf("action 5\n");
            rt_thread_mdelay(100);
        }

}
}

void thread2_entry(void *parameter)
{
    int i=0;
    for (i = 0; i < 5; ++i)
    {
        rt_mb_send(mail, i);
        rt_kprintf("mailbox send number%d\n",i);
        rt_thread_mdelay(500);
    }
    rt_kprintf("mailbox send end");
}

int mailbox_test(void)
{
    //创建邮箱
    mail = rt_mb_create("mb", 5, RT_IPC_FLAG_PRIO);
    if (mail == RT_NULL)
    {
        rt_kprintf("mailbox created failed\n");
    } else
    {
        rt_kprintf("mailbox created success\n");
    }

//创建线程1
    th1 = rt_thread_create("thread1",
                    thread1_entry,
                    RT_NULL,
                    512,
                    10,
                    10);
    if (th1 == RT_NULL)
    {
        rt_kprintf("thread1 create failed\n");
    } else
    {
        rt_kprintf("thread1 create success\n");
    }
    rt_thread_startup(th1);

//创建线程2
    th2 = rt_thread_create("thread2",
                    thread2_entry,
                    RT_NULL,
                    512,
                    10,
                    10);
    if (th2 == RT_NULL)
    {
        rt_kprintf("thread2 create failed\n");
    } else
    {
        rt_kprintf("thread2 create success\n");
    }
    rt_thread_startup(th2);

return 0;
}

```
传输的部分为：

```c
int i=0;
rt_mb_send(mail, i);
```
接受的部分为：
```c
rt_ubase_t val = RT_NULL;
if(rt_mb_recv(mail, &val, RT_WAITING_FOREVER) == RT_EOK)
```
实际调试结果也可以进行正常传输：

![screenshot_image.png](https://oss-club.rt-thread.org/uploads/20230226/0153d49b4b296628603435ec0d60dd68.png.webp)
我的这用法没问题吧，小白虚心请教
还望各位前辈指教！

张世争 2023-02-26

学以致用

超级无敌大王 2023-09-17

这家伙很懒，什么也没写！

您好，请问
如果传递一个结构体数据的话，需要保证结构体是【全局】的，传递时传递结构体变量的指针。
这个结构体必须是全局的吗？
我看到有的例程里面，传递的是局部变量的结构体指针，比方说下面这个

`static rt_mp_t tmp_msg_mp;    `
```c
static rt_mp_t tmp_msg_mp;    
struct recvdata                                    
{
    int timestamp;                               
    float data;                                            
};

static void data_receive_entry(void *parameter)
{
    struct recvdata buf;
    struct recvdata *buf_mp;

while (1)
    {
			/* 将时间戳存至buf */
			buf.timestamp = get_sensor_timestamp(); 
			/* 将传感器数据存至buf */
			buf.data = get_sensor_data(); 
			
            /* 申请一块内存 */
            buf_mp = rt_mp_alloc(tmp_msg_mp, RT_WAITING_FOREVER);
            buf_mp->data = buf.data;
			buf_mp->timestamp = buf.timestamp;
            rt_mb_send(tmp_msg_mb, (rt_ubase_t)buf_mp);
            buf_mp = NULL;
        }
        rt_thread_mdelay(200);
    }
}
```
这里面就是传递的局部变量的结构体指针，似乎是buf解析数据后，避免数据覆盖，先转存到buf_mp中再将buf_mp发送至邮箱，请问这样做会带来什么问题吗？

```c
buf_mp = NULL;
```

但上面这句没明白，如果刚发送完成就赋值NULL，不会造成数据处理线程越界吗，本人小白，虚心请教，感谢指点！🤞 😬