此文章方法可以一并结局重定向问题[[解决“_close is not implemented and will always fail”等编译警告]]。
重写__io_getchar函数和_read函数，即可重定向scanf输入：

int __io_getchar(void)
{
	uint8_t ch = 0;
	// Clear the Overrun flag just before receiving the first character
	__HAL_UART_CLEAR_OREFLAG(&huart1);
	HAL_UART_Receive(&huart1, (uint8_t *)&ch, 1, 0xFFFF);
	return ch;
}

__attribute__((weak)) int _read(int file, char *ptr, int len)
{
    (void)file;
    int DataIdx;
    for (DataIdx = 0; DataIdx < len; DataIdx++)
    {
        *ptr++ = __io_getchar();
    }
    return len;
}