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From: dave@lsuc.UUCP
Newsgroups: comp.lang.c,comp.unix.questions
Subject: printf %f rounds
Message-ID: <1767@lsuc.UUCP>
Date: Sun, 3-May-87 04:45:43 EDT
Article-I.D.: lsuc.1767
Posted: Sun May  3 04:45:43 1987
Date-Received: Sun, 3-May-87 09:30:59 EDT
Organization: Law Society of Upper Canada, Toronto
Lines: 21

This is probably old news to many people, but I was startled
to have it bite me. I've been programming in C for 11 years
and I thought I knew how printf behaved.

It appears that the behaviour of
	printf("%6.0f", x);
while standardized, is not documented in the v7 or System V manuals.
(X3J11 documents it correctly.)  printf rounds to the appropriate
number of digits.

I've usually written things like
	printf("%6d", (int)(x+0.5));
in the past, rounding by hand. I happened to use %.0f (and no cast)
recently, and I was surprised to find out that the +0.5 produces
wrong results in this case.

David Sherman
The Law Society of Upper Canada
Toronto
-- 
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