what is the use of #ifndefs

Ahmed Soliman ahmedsoliman0x666 at gmail.com
Mon Jul 20 06:03:07 EDT 2015

currently I started reading through the linux kernel and I started
reading liunx/include/linux/list.h> I understood some of the functions
but still I dont know what does these lines of code do
#ifndef _LINUX_LIST_H
#define _LINUX_LIST_H
which exist at the very beginning of the file
I also noticed that there is many similar ifndefs in almost any .h
file in the kernel
note that I understand wnat does ifndef do bu I dont understand what
goal is it supposed to achieve at the beginning of the headerfile

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