Xref: utzoo comp.lang.c:33907 comp.std.c:3933
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!usc!apple!veritas!amdcad!mozart.amd.com!usenet
From: tim@proton.amd.com (Tim Olson)
Newsgroups: comp.lang.c,comp.std.c
Subject: Parameter mismatch legality question
Message-ID: <1990Nov15.224353.155@mozart.amd.com>
Date: 15 Nov 90 22:43:53 GMT
Sender: usenet@mozart.amd.com (Usenet News)
Organization: Advanced Micro Devices; Sunnyvale, CA
Lines: 47

Here is an interesting question that came up recently.  What is the
"legality" of the following ("dusty deck" K&R, not ANSI) code:
	
	foo();
	
	bar()
	{
		int a;
		.
		.
		foo(a);
		.
		.
	}
	
	foo(a, b, c, d)
	int a, b, c, d;
	{
		.
		.
	}

i.e. the call to a function passes fewer parameters than are declared
in the function declaration.

Since C's parameters are "call-by-value", they can normally be
modified or destroyed by the called function.  What if a compiler with
dataflow analysis decided that the lifetimes for the parameter "b" and
a local variable were non-overlapping, and decided to use the same
space (be it memory or a register) to hold them?  In the case above,
it could end up overwriting some local variable from procedure bar()!

So the question is, is the code:

	a) Legal in all cases (at least for K&R C)

	b) Legal if there is no explicit modification of "optional"
	   variables

	c) Illegal

	d) Other?

--
	-- Tim Olson
	Advanced Micro Devices
	(tim@amd.com)