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From: ark@alice.att.com (Andrew Koenig)
Newsgroups: comp.std.c++
Subject: Re: Zero-length structures and pointer comparisons
Message-ID: <24398@alice.att.com>
Date: 12 Dec 92 19:56:40 GMT
Article-I.D.: alice.24398
References: <9234601.10277@mulga.cs.mu.OZ.AU> <1992Dec11.231131.10956@microsoft.com> <24392@alice.att.com> <1992Dec12.162211.5076@ucc.su.OZ.AU>
Reply-To: ark@alice.UUCP ()
Organization: AT&T Bell Laboratories, Murray Hill NJ
Lines: 38

In article <1992Dec12.162211.5076@ucc.su.OZ.AU> maxtal@extro.ucc.su.OZ.AU (John MAX Skaller) writes:

> >It shouldn't need to do that.  At most one trampoline is ever necessary
> >for a given nested function during its lifetime, namely the one that
> >binds the lexically surrounding context that was current when the
> >block containing the definition of that function was entered.

> 	Are you saying that if I have a recursive function with a nested
> function in it, and store the address of the nested function in scope
> at the time of entering the n'th recursion into an array in slot n,
> then executing the j'th slot will access the n'th activation record
> and not the j'th one? (I.e. all the functions in the array
> access the most recent activation record?)

No, that's just the opposite of that I said.

I said `the context that WAS current.'

Perhaps an example will make it clearer:

	void (*p)(void);
	void f(int n)
	{
		void g() { printf("%d\n", n); }
		if (n == 3)
			p = &g;
		if (n == 5)
			(*p)();
		else f(n+1);
	}

I am claiming that calling f(0) should print 3, not 5, because the
address stored in p should correspond to the stack frame in which
n is 3.  Indeed, that is just what gcc does.  It is also what every
other language I know does that supports such functions at all.
-- 
				--Andrew Koenig
				  ark@europa.att.com