opendarwin man page for difftime

DIFFTIME(3)                                                  Linux Programmer's Manual                                                 DIFFTIME(3)

NAME
       difftime - calculate time difference

SYNOPSIS
       #include <time.h>

       double difftime(time_t time1, time_t time0);

DESCRIPTION
       The  difftime()  function  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).

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       +-----------+---------------+---------+
       |Interface  | Attribute     | Value   |
       +-----------+---------------+---------+
       |difftime() | Thread safety | MT-Safe |
       +-----------+---------------+---------+
CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

NOTES
       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.

SEE ALSO
       date(1), gettimeofday(2), time(2), ctime(3), gmtime(3), localtime(3)

COLOPHON
       This  page is part of release 4.15 of the Linux 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/.

GNU                                                                 2015-08-08                                                         DIFFTIME(3)