Path: utzoo!attcan!uunet!salt.acc.com!ucsd!nprdc!stanonik
From: stanonik@nprdc.navy.mil (Ron Stanonik)
Newsgroups: u3b.misc,comp.unix.wizards
Subject: unsigned sizeof()
Message-ID: <6042@arctic.nprdc.arpa>
Date: 14 Feb 90 16:27:18 GMT
Sender: news@nprdc.arpa
Reply-To: stanonik@nprdc.navy.mil (Ron Stanonik)
Organization: Navy Personnel R&D Center, San Diego
Lines: 27

We ran into a "feature" while porting a program to our 3B2/600G
running sysV rel 3.2.2 V3: sizeof() returns unsigned.

The code looked like

	struct arf buf[MAX-1];
	while ((cnt = read(fd, buf, sizeof(buf))) >= sizeof(buf[0])) {
		do stuff with cnt arfs in buf
	}

The intent, apparently, is to reduce the number of reads by reading
several arf structs at once.  The problem occurs when the read returns
-1; since sizeof is unsigned the -1 is coerced into a big positive
number.

Yes, 2nd edition K&R says the result of sizeof is unsigned (though
it also says the type is implementation-defined, p204, which I find
contradictory).  Why though?  Why make sizeof unsigned?

Sorry if this is old news.  It was a surprise to us; ie, sizeof
on our suns and vax (4bsd) returns signed.

Thanks,

Ron Stanonik
stanonik@nprdc.navy.mil
ucsd!nprdc!stanonik