5 为什么rt_pin_get的异常返回值是-RT_ENOSYS (不在RT-Thread error code definitions范围内)，为什么加负号？

发布于 2023-01-18 15:53:13 浏览：492 订阅该版

RT-Thread的error code定义有0~10，一共11种，为什么[rt_pin_get](https://github.com/RT-Thread/rt-thread/blob/7ff64c1cfd2c3392f388ed91cd4955a064265c7f/components/drivers/misc/pin.c#L155)异常时[返回值](https://github.com/RT-Thread/rt-thread/blob/7ff64c1cfd2c3392f388ed91cd4955a064265c7f/components/drivers/misc/pin.c#L165 "返回值")是`-RT_ENOSYS`而不是`RT_ENOSYS`，这个`-`是为什么？

```c
/* RT-Thread error code definitions */
#define RT_EOK 0      /**< There is no error */
#define RT_ERROR 1    /**< A generic error happens */
#define RT_ETIMEOUT 2 /**< Timed out */
#define RT_EFULL 3    /**< The resource is full */
#define RT_EEMPTY 4   /**< The resource is empty */
#define RT_ENOMEM 5   /**< No memory */
#define RT_ENOSYS 6   /**< No system */
#define RT_EBUSY 7    /**< Busy */
#define RT_EIO 8      /**< IO error */
#define RT_EINTR 9    /**< Interrupted system call */
#define RT_EINVAL 10  /**< Invalid argument */
```
```c
rt_base_t rt_pin_get(const char *name)
{
    RT_ASSERT(_hw_pin.ops != RT_NULL);

if (name[0] != 'P' && name[0] != 'p')
    {
        return -RT_EINVAL;
    }
    if (_hw_pin.ops->pin_get == RT_NULL)
    {
        return -RT_ENOSYS;
    }
    return _hw_pin.ops->pin_get(name);
}
```