1TIME(P)                    POSIX Programmer's Manual                   TIME(P)
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NAME

6       time - get time
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SYNOPSIS

9       #include <time.h>
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11       time_t time(time_t *tloc);
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13

DESCRIPTION

15       The  time() function shall return the value of time    in seconds since
16       the Epoch.
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18       The tloc argument points to an area where  the  return  value  is  also
19       stored. If tloc is a null pointer, no value is stored.
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RETURN VALUE

22       Upon successful completion, time() shall return the value of time. Oth‐
23       erwise, (time_t)-1 shall be returned.
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ERRORS

26       No errors are defined.
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28       The following sections are informative.
29

EXAMPLES

31   Getting the Current Time
32       The following example uses the time() function to  calculate  the  time
33       elapsed, in seconds, since the Epoch, localtime() to convert that value
34       to a broken-down time, and asctime() to convert  the  broken-down  time
35       values into a printable string.
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37
38              #include <stdio.h>
39              #include <time.h>
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41
42              int main(void)
43              {
44              time_t result;
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46
47                  result = time(NULL);
48                  printf("%s%ju secs since the Epoch\n",
49                      asctime(localtime(&result)),
50                          (uintmax_t)result);
51                  return(0);
52              }
53
54       This example writes the current time to stdout in a form like this:
55
56
57              Wed Jun 26 10:32:15 1996
58              835810335 secs since the Epoch
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60   Timing an Event
61       The  following  example  gets  the  current  time, prints it out in the
62       user's format, and prints the number  of  minutes  to  an  event  being
63       timed.
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65
66              #include <time.h>
67              #include <stdio.h>
68              ...
69              time_t now;
70              int minutes_to_event;
71              ...
72              time(&now);
73              minutes_to_event = ...;
74              printf("The time is ");
75              puts(asctime(localtime(&now)));
76              printf("There are %d minutes to the event.\n",
77                  minutes_to_event);
78              ...
79

APPLICATION USAGE

81       None.
82

RATIONALE

84       The  time()  function  returns  a  value in seconds (type time_t) while
85       times() returns a set of values in clock ticks  (type  clock_t).   Some
86       historical implementations, such as 4.3 BSD, have mechanisms capable of
87       returning more precise times (see below). A generalized  timing  scheme
88       to  unify  these  various  timing  mechanisms has been proposed but not
89       adopted.
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91       Implementations in which time_t is a 32-bit signed integer  (many  his‐
92       torical  implementations)  fail in the year 2038.  IEEE Std 1003.1-2001
93       does not address this problem. However, the use of the time_t  type  is
94       mandated in order to ease the eventual fix.
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96       The use of the <time.h> header instead of <sys/types.h> allows compati‐
97       bility with the ISO C standard.
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99       Many historical implementations (including  Version  7)  and  the  1984
100       /usr/group  standard  use  long  instead  of  time_t.   This  volume of
101       IEEE Std 1003.1-2001 uses the latter type in order to  agree  with  the
102       ISO C standard.
103
104       4.3 BSD includes time() only as an alternate function to the more flex‐
105       ible gettimeofday() function.
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FUTURE DIRECTIONS

108       In a future version of this volume of IEEE Std 1003.1-2001,  time_t  is
109       likely  to  be  required to be capable of representing times far in the
110       future. Whether this will be mandated as a 64-bit type or a requirement
111       that a specific date in the future be representable (for example, 10000
112       AD) is not yet determined.  Systems purchased  after  the  approval  of
113       this  volume  of  IEEE Std 1003.1-2001 should be evaluated to determine
114       whether their lifetime will extend past 2038.
115

SEE ALSO

117       asctime() , clock() , ctime() , difftime() , gettimeofday() ,  gmtime()
118       , localtime() , mktime() , strftime() , strptime() , utime() , the Base
119       Definitions volume of IEEE Std 1003.1-2001, <time.h>
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122       Portions of this text are reprinted and reproduced in  electronic  form
123       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
124       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
125       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
126       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
127       event of any discrepancy between this version and the original IEEE and
128       The Open Group Standard, the original IEEE and The Open Group  Standard
129       is  the  referee document. The original Standard can be obtained online
130       at http://www.opengroup.org/unix/online.html .
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134IEEE/The Open Group                  2003                              TIME(P)
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