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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: typeof isn't enough to define swap correctly
Message-ID: <8415@mimsy.UUCP>
Date: Fri, 4-Sep-87 19:08:57 EDT
Article-I.D.: mimsy.8415
Posted: Fri Sep  4 19:08:57 1987
Date-Received: Sat, 5-Sep-87 20:57:13 EDT
References: <557@rocky.STANFORD.EDU> <1880@sol.ARPA>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 19

This should work even without typeof().  I do not recommend it.
Note that you will get warnings from PCC if SWAP is applied to
arrays.  You can remove the sizeof/panic code if you dare.

	#define SWAP(a, b) { \
		struct __t { char bytes[sizeof(a)]; }; \
		struct __t *__a = (struct __t *)&(a); \
		struct __t *__b = (struct __t *)&(b); \
		struct __t __t; \
		if (sizeof(struct __t) != sizeof(b)) \
			panic("bad swap() args: %s, line %d", \
				__FILE__, __LINE__); \
		__t = *__a; \
		*__a = *__b; \
		*__b = __t; \
	}
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris