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Path: utzoo!linus!security!genrad!mit-eddie!mp
From: mp@mit-eddie.UUCP (Mark Plotnick)
Newsgroups: net.lang.c
Subject: ++ operator
Message-ID: <1092@mit-eddie.UUCP>
Date: Sun, 25-Dec-83 17:30:47 EST
Article-I.D.: mit-eddi.1092
Posted: Sun Dec 25 17:30:47 1983
Date-Received: Mon, 26-Dec-83 04:10:07 EST
References: <122@taurus.UUCP>
Organization: MIT, Cambridge, MA
Lines: 27

dave@taurus notes:
	Uh-uh:
		if(*in++ == *in++)

	...

	Also, for those of little faith, there are actually C compilers that
	will take the non-obvious meaning of this (e.g. the PDP-11 cc), and do
	the tests then do both increments in one go after the statement,
	so BE WARNED.

I just tried this with the V7 cc, 4.1bsd pcc, and VAX-11 C compilers, and in
each case two increments were done.

The reference manual is vague here, but a good rule of thumb is that
foo++ is equivalent to ((foo=foo+1)-1).  I don't know of any exceptions
to this off-hand, although I heard that a pcc author was once thinking of
delaying the postincrement of function args until after the function call
[i.e. f(i++) would be equivalent to (temp=f(i),i++,temp) ].

Since there are still quite a few C compilers being written from
scratch out there, it would really help if someone were to come up with
a precise, consistent definition for how the postincrement and
postdecrement operators should behave.  Ditto for enum, void,
unsigned chars, non-integer bitfields, etc.

	Mark