mac fatal error: 'stdlib.h' file not found

//1.检查头文件是否存在

$clang++ -E -x c++ - -v < /dev/null

ignoring nonexistent directory "/usr/include/c++/v1"
ignoring nonexistent directory "/usr/include"

注：说明macOS SDK 的头文件不存在

//2.安装xcode-select

$xcode-select --install 

//3.获取header pkg

$xcode-select -p 

//4.查看config

$brew config

//5.安装头文件

$ cd /Library/Developer/CommandLineTools/Packages/

$ open macOS_SDK_headers_for_macOS_10.14.pkg