Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!xanth!mcnc!rti!xyzzy!agarn!throopw
From: throopw@agarn.dg.com (Wayne A. Throop)
Newsgroups: comp.lang.c
Subject: Re: Recursive #includes
Keywords: recursive includes, modularity
Message-ID: <3851@xyzzy.UUCP>
Date: 7 Mar 89 20:21:00 GMT
References: <570@marob.MASA.COM> <9727@smoke.BRL.MIL> <964@philmds.UUCP> <3804@xyzzy.UUCP> <7488@june.cs.washington.edu> <11959@haddock.ima.isc.com>
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> karl@haddock.ima.isc.com (Karl Heuer)
>> ka@june.cs.washington.edu (Kenneth Almquist)
>>I've been told that incomplete types cannot be used in function
>>prototypes.  For example,
>>	void f(struct s *);
>>	struct s { ... };
>>	void f(struct s *p) { ... }
>>is illegal ...
> Yes it is illegal, but due to a scoping problem, not a restriction against
> incomplete types.  Adding the empty declaration `struct s;' at the top should
> cause it to become legal.  (I just tested this with gcc.)

Testing it with DG C, this amusing, almost inscrutable, (though in
spirit quite correct) error message resulted:

    You have already declared "f" as a variable,
    enumeration, or typedef in the current block with different type
    attributes.  The following are the previous and current types:
            Previous type: void (struct s *)
            Current  type: void (struct s *)

Note, however, that incompleted types can still be used to break the
kinds of cycles I was talking about, since (as Karl points out) this
is a scoping problem not encountered in derivatives of the example I
gave.

--
"Is it an infinite loop?"
"I dunno... it sure is *persistent*, anyhow."
                              --- unknown
--
Wayne Throop      <the-known-world>!mcnc!rti!xyzzy!throopw