From mboxrd@z Thu Jan  1 00:00:00 1970
From: navych@126.com (Navy)
Date: Tue, 21 Jul 2015 10:24:45 +0800
Subject: what is the use of #ifndefs
In-Reply-To: <CAAGnT3auLPQqtOZv+4sdf4UyesdEz3tdPkzao0AyUmQ5C9Hbcg@mail.gmail.com>
References: <CAAGnT3auLPQqtOZv+4sdf4UyesdEz3tdPkzao0AyUmQ5C9Hbcg@mail.gmail.com>
Message-ID: <20150721022445.GA2368@debian>
To: kernelnewbies@lists.kernelnewbies.org
List-Id: kernelnewbies.lists.kernelnewbies.org

On Mon, Jul 20, 2015 at 12:03:07PM +0200, Ahmed Soliman wrote:
> 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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The whole structure seems to 
#ifndef ...
#define ...
.
.
.
#endif