说明：  对读入一个字节（不带回车）读入一个字符串带回车，发送字符串函数测试成功 由于不清楚keil自带的STDIO.H函数是否是堵塞发送接受，所以本程序使用非堵塞方式发送接受，缺点是占 用一些内存，缓冲区大小可自由配置。
(To read into a byte (not back to the car) read into a string back to the car, send the string function to test the success of its own as a result of the stdio.h keil unclear whether it is to plug a send function to accept, so the program uses non-blocking sent to accept, is occupied by some of the shortcomings of memory, the freedom to configure the buffer size.)