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From: rfg@lupine.ncd.com (Ron Guilmette)
Newsgroups: comp.std.c
Subject: A question on volatile accesses
Message-ID: <2388@lupine.NCD.COM>
Date: 3 Nov 90 03:47:00 GMT
Sender: rfg@NCD.COM
Organization: Network Computing Devices, Inc., Mt. View, CA
Lines: 39

Given the following code:

	volatile int *ip;

	void foobar ()
	{
		register int i;

		do
			i = *++ip;
		while (i);
	}

I'd like to know if the standard allows the incrementation of `ip'
to occur *after* the volatile access.

In other words, could the program above legally be treated as:

	volatile int *ip;

	void foobar ()
	{
		register int i;

		do {
			i = *ip;
			++ip;
		} while (i);
	}

This seems entirely counter-intutive to me, and yet one supposedly ANSI
C compiler provides such a treatment.

I guess the question comes down to this: When you dereference a
pre-incremented pointer, can you always safely assume that the
pre-increment has already occured by the time the indirection
through the pointer occurs?

Note that the variable `ip' is not itself volatile.