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From: wirzeniu@klaava.Helsinki.FI (Lars Wirzenius)
Newsgroups: comp.lang.c
Subject: Re: Time Info
Summary: Use difftime, oops, don't have it, try 'now - then' instead.
Keywords: time accounting
Message-ID: <1991May26.084809.4636@klaava.Helsinki.FI>
Date: 26 May 91 08:48:09 GMT
References: <39@neis.UUCP>
Organization: University of Helsinki
Lines: 44

In article <39@neis.UUCP> molnar@neis.UUCP (Christopher Molnar) writes:
>I am writing a C routine that needs to compare a start time and
>the current time and have the result in minute.
>
>Can any-one suggest where to find this in the Xenix reffereance manuals
>or suggest a way I can accomplish this?

The standard library function difftime returns the difference in seconds
between two times (represented as time_t's, i.e.  whatever time()
returns).  This is easy to convert to minutes:

	time_t then, now;
	double secs, mins;			/* difftime returns
						 * double
						 */

	time(&then);
	.....
	time(&now);

	secs = difftime(then, now);
	mins = secs / 60.0; 			/* you could do some
						 * rounding here, if you
						 * prefer
						 */

Oops. I just checked my manuals for Xenix, and it seems that it
doesn't have difftime. :-(

In that case one needs to take advantage of the fact that time_t on SCO
Xenix (and most of the Unix world) is a long that tells the seconds
since the beginning of the Era (January 1, 1970, at 00:00:00 GMT), so
the difftime can be replaced by

	secs = (double) (now - then);		/* of course, you could
						 * use long for secs now,
						 * but that would make it
						 * more difficult to use
						 * difftime in the future.
						 */

and the rest is identical.
-- 
Lars Wirzenius     wirzeniu@cc.helsinki.fi