最近经常遇到这个报错：
Implicit declaration of function 'select' is invalid in C99
还有这个：
Declaration of 'select' must be imported from module 'Darwin.POSIX.sys.time' before it is required
如下图：
Screen Shot 2017-10-27 at 15.19.00.png
解决办法：
导入头文件：#include <sys/time.h>