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From: ed@mtxinu.UUCP (Ed Gould)
Newsgroups: net.unix,net.bugs.4bsd
Subject: Re: Compiler bug
Message-ID: <364@mtxinu.UUCP>
Date: Tue, 7-May-85 12:15:49 EDT
Article-I.D.: mtxinu.364
Posted: Tue May  7 12:15:49 1985
Date-Received: Sun, 12-May-85 01:46:13 EDT
References: <121@galbp.UUCP>
Distribution: net
Organization: mt Xinu, Berkeley, CA
Lines: 40
Xref: linus net.unix:3876 net.bugs.4bsd:1211

> I noticed this idiosyncrasy with regards to our C compiler.  Given the
> following
> 
> >	int	a;
> >	int	a;
> >
> >	main()
> >	{
> >		for (;;)
> >			;
> >	}
> 
> When compiling this, the compiler generates no error messages.  Seems
> to me, it should give a "redeclaration of a" error message.  It does
> give the error message, if the two int's are made automatic variables
> (i.e., declared within main()).
> 
> ... running 4.2BSD.

The C language allows multiple definitions of *external* variables.
In all (that I know of, anyway) implementations under Unix declarations
made outside of a function are external - not just to the functions
in that file, but to the file as well.

Some AT&T compilers - specifically those on System V - complain about
the construction you describe.  Lots of folks have griped about that!
If the declarations *within* one file aren't consistent, e.g.,

	int a;
	struct {
	    int c;
	    int d;
	} a;

any compiler should complain.  (Of course, there is *no* checking
if the declarations are in separately-compiled files!)

-- 
Ed Gould		    mt Xinu, 2910 Seventh St., Berkeley, CA  94710  USA
{ucbvax,decvax}!mtxinu!ed   +1 415 644 0146