Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!ames!haven!adm!smoke!gwyn
From: gwyn@smoke.brl.mil (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: typedefs that need each other
Message-ID: <14826@smoke.brl.mil>
Date: 11 Jan 91 23:11:22 GMT
References: <26261@uflorida.cis.ufl.EDU>
Organization: U.S. Army Ballistic Research Laboratory, APG, MD.
Lines: 20

In article <26261@uflorida.cis.ufl.EDU> jdb@reef.cis.ufl.edu (Brian K. W. Hook) writes:
>typedef struct _struct1 {
>	STRUCT2 *structure;
>} STRUCT1;
>typedef struct _struct2 {
>	STRUCT1 *structure;
>} STRUCT2;

You cannot use an identifier as a typedef before the identifer IS a typedef!
However, you can use incomplete types in contexts such as this.  For instance:

struct _struct2;	/* optional in most cases, but recommended */
struct _struct1 {
	struct _struct2 *structure;
};
struct _struct2 {
	struct _struct1 *structure;
};
typedef struct _struct1 STRUCT1;
typedef struct _struct2 STRUCT2;