From:	"DeHackEd" <notgiven AT out DOT com>
Newsgroups:	comp.os.msdos.djgpp
References:	<37245860 DOT 11385716 AT 158 DOT 152 DOT 254 DOT 70>
Subject:	Re: Header files
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Message-ID:	<LNKU2.3222$ho1.938@tundra.ops.attcanada.net>
Date:	Sun, 25 Apr 1999 20:19:55 GMT
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

<sam AT greenaumARSE!ARSE!ARSE!.demon.co.uk> wrote in message
news:37245860 DOT 11385716 AT 158 DOT 152 DOT 254 DOT 70...
> I just don't get header files and what "extern" actually means. I want
Ok, here's the way it works. The following are 2 declarations of a variable:

// This line can only show up in exactly 1 C file
int foo;


// This line can show up anywhere, and is merely informative
extern int foo;

// This is illegal
extern int foo = 27;

If you say extern, then the compiler knows it does exist but not here. If you
don't use extern, it's actually declared. If you declare it in more than 1 file,
the linker rejects it.

> to break up a long program, so I've put all the declarations, from the
> first #define up til main(), into a .h file.
>
> I've put some of the functions into one .C file, and the rest into
> another, and included my .h file in both.
>
> It gives me "multiple definition of blablah" a lot of times.

Remeber that the H file contains the word extern and only 1 C file contains the
real declaration. Both EXTERN and actually declaring the variable in the same
file (or including it) will not conflict or cause errors.

>
> What do I actually do, what does extern mean? I realise it's simple
> but it's a big project and I don't want to mess anything up then have
> some obscure bug pop up later and torment me not knowing what it is.

You're just modifying a project right? As long as you don't modify the actual
code, you have nothing to worry about so long as the linker accepts the file and
does not give errors.


> ------------------------------------------------------------------------
> well I try my best, to be just like I am
> but everybody wants you to be jeeeiiiist like them
> they say "sing while you slave", but I just get bored,
>
>            http://www.greenaum.demon.co.uk/
>
> Protect privacy, boycott Intel: http://www.bigbrotherinside.org

Now this I have got to see.



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"DeHackEd"

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