1TIME(2) Linux Programmer's Manual TIME(2)
2
6 time - get time in seconds
7
9 #include <time.h>
10 time_t time(time_t *tloc);
12
14 time() returns the time as the number of seconds since the Epoch,
15 1970-01-01 00:00:00 +0000 (UTC).
16 If tloc is non-NULL, the return value is also stored in the memory
18 pointed to by tloc.
19
21 On success, the value of time in seconds since the Epoch is returned.
22 On error, ((time_t) -1) is returned, and errno is set to indicate the
23 error.
24
26 EFAULT tloc points outside your accessible address space (but see
27 BUGS).
28 On systems where the C library time() wrapper function invokes
30 an implementation provided by the vdso(7) (so that there is no
31 trap into the kernel), an invalid address may instead trigger a
32 SIGSEGV signal.
33
35 SVr4, 4.3BSD, C89, C99, POSIX.1-2001. POSIX does not specify any error
36 conditions.
37
39 POSIX.1 defines seconds since the Epoch using a formula that approxi‐
40 mates the number of seconds between a specified time and the Epoch.
41 This formula takes account of the facts that all years that are evenly
42 divisible by 4 are leap years, but years that are evenly divisible by
43 100 are not leap years unless they are also evenly divisible by 400, in
44 which case they are leap years. This value is not the same as the ac‐
45 tual number of seconds between the time and the Epoch, because of leap
46 seconds and because system clocks are not required to be synchronized
47 to a standard reference. The intention is that the interpretation of
48 seconds since the Epoch values be consistent; see POSIX.1-2008 Ratio‐
49 nale A.4.15 for further rationale.
50 On Linux, a call to time() with tloc specified as NULL cannot fail with
52 the error EOVERFLOW, even on ABIs where time_t is a signed 32-bit inte‐
53 ger and the clock ticks past the time 2**31 (2038-01-19 03:14:08 UTC,
54 ignoring leap seconds). (POSIX.1 permits, but does not require, the
55 EOVERFLOW error in the case where the seconds since the Epoch will not
56 fit in time_t.) Instead, the behavior on Linux is undefined when the
57 system time is out of the time_t range. Applications intended to run
58 after 2038 should use ABIs with time_t wider than 32 bits.
59
61 Error returns from this system call are indistinguishable from success‐
62 ful reports that the time is a few seconds before the Epoch, so the C
63 library wrapper function never sets errno as a result of this call.
64 The tloc argument is obsolescent and should always be NULL in new code.
66 When tloc is NULL, the call cannot fail.
67 C library/kernel differences
69 On some architectures, an implementation of time() is provided in the
70 vdso(7).
71
73 date(1), gettimeofday(2), ctime(3), ftime(3), time(7), vdso(7)
74
76 This page is part of release 5.12 of the Linux man-pages project. A
77 description of the project, information about reporting bugs, and the
78 latest version of this page, can be found at
79 https://www.kernel.org/doc/man-pages/.
80Linux 2021-03-22 TIME(2)