#indef

Question

What's the purpose of "if not defined", if you already define with #define

Answer 1

http://stackoverflow.com/questions/1653958/why-are-ifndef-and-define-used-in-c-header-files

Answer 2

#pragma is a good alternative for #indef and #define if you have a compiler that supports it (most do)

https://en.m.wikipedia.org/wiki/Pragma_once

ref:Nikolay Jivkov