Manpage of TIME
TIMESection: Linux Programmer's Manual (2)
NAMEtime - get time in seconds
DESCRIPTIONtime() returns the time as the number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
RETURN VALUEOn success, the value of time in seconds since the Epoch is returned. On error, ((time_t) -1) is returned, and errno is set appropriately.
- tlocpoints outside your accessible address space (but see BUGS).
- On systems where the C library time() wrapper function invokes an implementation provided by the vdso(7) (so that there is no trap into the kernel), an invalid address may instead trigger a SIGSEGVsignal.
CONFORMING TOSVr4, 4.3BSD, C89, C99, POSIX.1-2001. POSIX does not specify any error conditions.
NOTESPOSIX.1 defines seconds since the Epochusing a formula that approximates the number of seconds between a specified time and the Epoch. This formula takes account of the facts that all years that are evenly divisible by 4 are leap years, but years that are evenly divisible by 100 are not leap years unless they are also evenly divisible by 400, in which case they are leap years. This value is not the same as the actual number of seconds between the time and the Epoch, because of leap seconds and because system clocks are not required to be synchronized to a standard reference. The intention is that the interpretation of seconds since the Epoch values be consistent; see POSIX.1-2008 Rationale A.4.15 for further rationale.
On Linux, a call to time() with tlocspecified as NULL cannot fail with the error EOVERFLOW, even on ABIs where time_tis a signed 32-bit integer and the clock ticks past the time 2**31 (2038-01-19 03:14:08 UTC, ignoring leap seconds). (POSIX.1 permits, but does not require, the EOVERFLOWerror in the case where the seconds since the Epoch will not fit in time_t.) Instead, the behavior on Linux is undefined when the system time is out of the time_trange. Applications intended to run after 2038 should use ABIs with time_twider than 32 bits.
BUGSError returns from this system call are indistinguishable from successful reports that the time is a few seconds beforethe Epoch, so the C library wrapper function never sets errnoas a result of this call.
SEE ALSOdate(1), gettimeofday(2), ctime(3), ftime(3), time(7), vdso(7)
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