man3/difftime.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  25 .\" References consulted:
  26 .\"     Linux libc source code
  27 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  28 .\"     386BSD man pages
  29 .\" Modified Sat Jul 24 19:48:17 1993 by Rik Faith (faith@cs.unc.edu)
  30 .TH DIFFTIME 3  2015-03-02 "GNU" "Linux Programmer's Manual"
  31 .SH NAME
  32 difftime \- calculate time difference
  33 .SH SYNOPSIS
  34 .nf
  35 .B #include <time.h>
  36 .sp
  37 .BI "double difftime(time_t " time1 ", time_t " time0 );
  38 .fi
  39 .SH DESCRIPTION
  40 The
  41 .BR difftime ()
  42 function returns the number of seconds elapsed
  43 between time \fItime1\fP and time \fItime0\fP, represented as a
  44 .IR double .
  45 Each of the times is specified in calendar time, which means its
  46 value is a measurement (in seconds) relative to the
  47 Epoch, 1970-01-01 00:00:00 +0000 (UTC).
  48 .SH ATTRIBUTES
  49 For an explanation of the terms used in this section, see
  50 .BR attributes (7).
  51 .TS
  52 allbox;
  53 lb lb lb
  54 l l l.
  55 Interface       Attribute       Value
  56 T{
  57 .BR difftime ()
  58 T}      Thread safety   MT-Safe
  59 .TE
  60 .SH CONFORMING TO
  61 POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
  62 .SH NOTES
  63 On a POSIX system,
  64 .I time_t
  65 is an arithmetic type, and one could just
  66 define
  67 .RS
  68 .nf
  69
  70 #define difftime(t1,t0) (double)(t1 \- t0)
  71
  72 .fi
  73 .RE
  74 when the possible overflow in the subtraction is not a concern.
  75 .SH SEE ALSO
  76 .BR date (1),
  77 .BR gettimeofday (2),
  78 .BR time (2),
  79 .BR ctime (3),
  80 .BR gmtime (3),
  81 .BR localtime (3)