man3/difftime.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\" References consulted:
   6 .\"     Linux libc source code
   7 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
   8 .\"     386BSD man pages
   9 .\" Modified Sat Jul 24 19:48:17 1993 by Rik Faith (faith@cs.unc.edu)
  10 .TH DIFFTIME 3  2021-03-22 "Linux man-pages (unreleased)"
  11 .SH NAME
  12 difftime \- calculate time difference
  13 .SH LIBRARY
  14 Standard C library
  15 .RI ( libc ", " \-lc )
  16 .SH SYNOPSIS
  17 .nf
  18 .B #include <time.h>
  19 .PP
  20 .BI "double difftime(time_t " time1 ", time_t " time0 );
  21 .fi
  22 .SH DESCRIPTION
  23 The
  24 .BR difftime ()
  25 function returns the number of seconds elapsed
  26 between time \fItime1\fP and time \fItime0\fP, represented as a
  27 .IR double .
  28 Each of the times is specified in calendar time, which means its
  29 value is a measurement (in seconds) relative to the
  30 Epoch, 1970-01-01 00:00:00 +0000 (UTC).
  31 .SH ATTRIBUTES
  32 For an explanation of the terms used in this section, see
  33 .BR attributes (7).
  34 .ad l
  35 .nh
  36 .TS
  37 allbox;
  38 lbx lb lb
  39 l l l.
  40 Interface       Attribute       Value
  41 T{
  42 .BR difftime ()
  43 T}      Thread safety   MT-Safe
  44 .TE
  45 .hy
  46 .ad
  47 .sp 1
  48 .SH STANDARDS
  49 POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
  50 .SH NOTES
  51 On a POSIX system,
  52 .I time_t
  53 is an arithmetic type, and one could just
  54 define
  55 .PP
  56 .in +4n
  57 .EX
  58 #define difftime(t1,t0) (double)(t1 \- t0)
  59 .EE
  60 .in
  61 .PP
  62 when the possible overflow in the subtraction is not a concern.
  63 .SH SEE ALSO
  64 .BR date (1),
  65 .BR gettimeofday (2),
  66 .BR time (2),
  67 .BR ctime (3),
  68 .BR gmtime (3),
  69 .BR localtime (3)