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From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.std.c
Subject: Re: Multiple typedefs
Keywords: typedefs, includes, defines
Message-ID: <10190@smoke.BRL.MIL>
Date: 2 May 89 05:38:25 GMT
References: <2322@lethe.UUCP> <10167@smoke.BRL.MIL> <2402@lethe.UUCP>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 13

In article <2402@lethe.UUCP> dave@lethe.UUCP (Dave Collier-Brown) writes:
>  Is there a technical reason for the difference in redefinition rules
>for macros -vs- typedefs, ...?

Yes.

Oh, you want to know what it is?  Well, consider how the compiler is
going to parse a complex declaration containing several typedefs.
How does it know whether you are defining the same typedef a second
time or are just using it to help typedef something else?

There's no analogous problem with #define, due to its unambiguous
syntax that makes it clear what identifier is being defined.