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From: dir@obo586.UUCP (Dan Rosenblatt)
Newsgroups: net.lang.c
Subject: sizeof() didn't produce expected value, but it wasn't wrong
Message-ID: <126@obo586.UUCP>
Date: Fri, 3-May-85 00:38:27 EDT
Article-I.D.: obo586.126
Posted: Fri May  3 00:38:27 1985
Date-Received: Mon, 6-May-85 01:38:39 EDT
Organization: obo Systems Inc., Aurora, Colorado
Lines: 28

[]
A function I wrote for some graphics software looked something like:

vecmul(invec,inmat,outvec)
double invec[3],inmat[3][3],outvec[3];
{
	int i,j;
	double tmpvec[3];

	for (i=0;i<3;++i) {
		tmpvec[i] = 0.;
		for (j=0;j<3;++j)
			tmpvec[i] += invec[j] * inmat[i][j];
	}
	bcopy((char *)outvec,(char *)tmpvec,sizeof(outvec));
}

The calling sequence for bcopy was: (dst,src,size_in_bytes).
The problem is that 'sizeof(outvec)' produced the value 2
instead of what I expected - 24.  The reason is (as I kick
myself around the room :-}) is that an array which is a parameter
to a function becomes a pointer to that array.  The 2 comes
from the fact that I'm running on a 16-bit 8086 chip. 'nuf said.


Dan Rosenblatt
obo Systems, Inc.
...{ihnp4!denelcor,nbires!gangue}!obo586!dir