.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" %%%LICENSE_START(VERBATIM)
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.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
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.\" manual under the conditions for verbatim copying, provided that the
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 19:48:17 1993 by Rik Faith (faith@cs.unc.edu)
.TH DIFFTIME 3  2015-08-08 "GNU" "Linux Programmer's Manual"
.SH NAME
difftime \- calculate time difference
.SH SYNOPSIS
.nf
.B #include <time.h>
.sp
.BI "double difftime(time_t " time1 ", time_t " time0 );
.fi
.SH DESCRIPTION
The
.BR difftime ()
function returns the number of seconds elapsed
between time \fItime1\fP and time \fItime0\fP, represented as a
.IR 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).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lb lb lb
l l l.
Interface	Attribute	Value
T{
.BR difftime ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
.SH NOTES
On a POSIX system,
.I time_t
is an arithmetic type, and one could just
define
.RS
.nf

#define difftime(t1,t0) (double)(t1 \- t0)

.fi
.RE
when the possible overflow in the subtraction is not a concern.
.SH SEE ALSO
.BR date (1),
.BR gettimeofday (2),
.BR time (2),
.BR ctime (3),
.BR gmtime (3),
.BR localtime (3)
.SH COLOPHON
This page is part of release 4.10 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.