Section (3) difftime
difftime — calculate time difference
returns the number of seconds elapsed between time
time1 and time
time0, represented as a
double. Each of the times is
specified in calendar time, which means its value is a
measurement (in seconds) relative to the Epoch, 1970-01-01
00:00:00 +0000 (UTC).
For an explanation of the terms used in this section, see attributes(7).
On a POSIX system, time_t is an arithmetic type, and one could just define
#define difftime(t1,t0) (double)(t1 − t0)
when the possible overflow in the subtraction is not a concern.
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Copyright 1993 David Metcalfe (davidprism.demon.co.uk)
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Linux libc source code
Lewine_zsingle_quotesz_s _POSIX Programmer_zsingle_quotesz_s Guide_ (O_zsingle_quotesz_Reilly & Associates, 1991)
386BSD man pages
Modified Sat Jul 24 19:48:17 1993 by Rik Faith (faithcs.unc.edu)