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'\" t
.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" 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 2023-07-20 "Linux man-pages 6.05.01"
.SH NAME
difftime \- calculate time difference
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <time.h>
.PP
.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;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR difftime ()
T} Thread safety MT-Safe
.TE
.sp 1
.SH STANDARDS
C11, POSIX.1-2008.
.SH HISTORY
POSIX.1-2001, C89, SVr4, 4.3BSD.
.SH NOTES
On a POSIX system,
.I time_t
is an arithmetic type, and one could just
define
.PP
.in +4n
.EX
#define my_difftime(t1,t0) (double)(t1 \- t0)
.EE
.in
.PP
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)
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