Xcode 9 遇到：Implicit declaration

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>