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From: jeenglis@nunki.usc.edu (Joe English)
Newsgroups: comp.lang.c
Subject: Re: on the fringe of C syntax/semantics
Message-ID: <5560@merlin.usc.edu>
Date: 6 Oct 89 19:52:57 GMT
References: <80100001@bonzo> <453@usage.csd.unsw.oz>
Sender: news@merlin.usc.edu
Reply-To: jeenglis@nunki.usc.edu (Joe English)
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Organization: University of Southern California, Los Angeles, CA
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troy@mr_plod.cbme.unsw.oz writes:
>This isn't really on the edge of the language specs.... although I ran into
>a question last night which was... somebody wanted to define a pair of
>structures which were initialised with pointers to eachother. 
[...]
>struct a_struct {
>	void *next;
>	int value;
>};
>
>struct b_struct {
>	struct a_struct *next;
>	int value;
>};


Except you probably shouldn't use void *.  I just tried this,
and both gcc and cc (SunOS) accepted it:

struct foo;	/* forward declaration -- unnecessary, though */

struct bar {
	struct foo *foop; /* this is OK. */
};

struct foo {
	struct bar *barp; /* OK, struct bar seen alrerady */
	struct diddle *diddlep; /* OK, struct diddle defined later */
	struct qwerty *qwertyp; /* OK, struct qwerty *never* defined */
};

struct diddle {
	int asdf;
};


Presumably the compiler would complain if I tried to
use a foo::qwertyp before it had seen the definition
of struct qwerty, but the rest worked just fine.

(BTW, is this behaviour specified in the standard?)

--Joe English

  jeenglis@nunki.usc.edu