From: dontmailme AT iname DOT com (Steamer)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Pointers and Arrays (Newbie)
Date: Wed, 28 Jun 2000 12:05:31 GMT
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To: djgpp AT delorie DOT com
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Adrian Smith wrote:

> That seems to cure it ! Could somebody explain to me why and what the
> 'extern' statement is used for in this context.

You should check a good reference book (or even the standard itself)
for full details about 'extern'.  But in this context, the extern
declaration

extern const char * message;

tells the compiler that the object 'message' has type 'const char*'
and has external linkage.  Once the compiler has seen this declaration
it knows enough about 'message' to correctly compile any code that
uses it.  But the extern declaration doesn't actually create an object,
so there needs to be an actual definition somewhere.  You can put the
definition in any source file.  (But you can only put it in one source
file, otherwise you have multiple objects with external linkage all
sharing the same name, which is not possible.  This is what you were
doing wrong, because you were #including a definition into two different
source files.)

S.