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time(3p) — Linux manual page

PROLOG \|NAME \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|EXAMPLES \|APPLICATION USAGE \|RATIONALE \|FUTURE DIRECTIONS \|SEE ALSO \|COPYRIGHT

TIME(3P)                POSIX Programmer's ManualTIME(3P)

PROLOG top

       This manual page is part of the POSIX Programmer's Manual.  The       Linux implementation of this interface may differ (consult the       corresponding Linux manual page for details of Linux behavior), or       the interface may not be implemented on Linux.

NAME top

       time — get time

SYNOPSIS top

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

DESCRIPTION top

       The functionality described on this reference page is aligned with       the ISO C standard. Any conflict between the requirements       described here and the ISO C standard is unintentional. This       volume of POSIX.1‐2017 defers to the ISO C standard.       Thetime() function shall return the value of time in seconds       since the Epoch.       Thetloc argument points to an area where the return value is also       stored. Iftloc is a null pointer, no value is stored.

RETURN VALUE top

       Upon successful completion,time() shall return the value of time.       Otherwise, (time_t)-1 shall be returned.

ERRORS top

       Thetime() function may fail if:EOVERFLOW              The number of seconds since the Epoch will not fit in an              object of typetime_t.The following sections are informative.

EXAMPLES top

Getting the Current Time       The following example uses thetime() function to calculate the       time elapsed, in seconds, since the Epoch,localtime() to convert       that value to a broken-down time, andasctime() to convert the       broken-down time values into a printable string.           #include <stdio.h>           #include <time.h>           int main(void)           {           time_t result;               result = time(NULL);               printf("%s%ju secs since the Epoch\n",                   asctime(localtime(&result)),                       (uintmax_t)result);               return(0);           }       This example writes the current time tostdout in a form like       this:           Wed Jun 26 10:32:15 1996           835810335 secs since the EpochTiming an Event       The following example gets the current time, prints it out in the       user's format, and prints the number of minutes to an event being       timed.           #include <time.h>           #include <stdio.h>           ...           time_t now;           int minutes_to_event;           ...           time(&now);           minutes_to_event = ...;           printf("The time is ");           puts(asctime(localtime(&now)));           printf("There are %d minutes to the event.\n",               minutes_to_event);           ...

APPLICATION USAGE top

       None.

RATIONALE top

       Thetime() function returns a value in seconds whileclock_gettime() andgettimeofday() return astruct timespec       (seconds and nanoseconds) andstruct timeval(seconds and       microseconds), respectively, and are therefore capable of       returning more precise times. Thetimes() function is also capable       of more precision thantime() as it returns a value in clock       ticks, although it returns the elapsed time since an arbitrary       point such as system boot time, not since the epoch.       Implementations in whichtime_tis a 32-bit signed integer (many       historical implementations) fail in the year 2038. POSIX.1‐2008       does not address this problem. However, the use of thetime_ttype       is mandated in order to ease the eventual fix.       On some systems thetime() function is implemented using a system       call that does not return an error condition in addition to the       return value. On these systems it is impossible to differentiate       between valid and invalid return values and hence overflow       conditions cannot be reliably detected.       The use of the<time.h> header instead of<sys/types.h> allows       compatibility with the ISO C standard.       Many historical implementations (including Version 7) and the 1984       /usr/group standard uselonginstead oftime_t.  This volume of       POSIX.1‐2017 uses the latter type in order to agree with the ISO C       standard.

FUTURE DIRECTIONS top

       In a future version of this volume of POSIX.1‐2017,time_tis       likely to be required to be capable of representing times far in       the future. Whether this will be mandated as a 64-bit type or a       requirement that a specific date in the future be representable       (for example, 10000 AD) is not yet determined. Systems purchased       after the approval of this volume of POSIX.1‐2017 should be       evaluated to determine whether their lifetime will extend past       2038.

COPYRIGHT top

       Portions of this text are reprinted and reproduced in electronic       form from IEEE Std 1003.1-2017, Standard for Information       Technology -- Portable Operating System Interface (POSIX), The       Open Group Base Specifications Issue 7, 2018 Edition, Copyright       (C) 2018 by the Institute of Electrical and Electronics Engineers,       Inc and The Open Group.  In the event of any discrepancy between       this version and the original IEEE and The Open Group Standard,       the original IEEE and The Open Group Standard is the referee       document. The original Standard can be obtained online athttp://www.opengroup.org/unix/online.html .       Any typographical or formatting errors that appear in this page       are most likely to have been introduced during the conversion of       the source files to man page format. To report such errors, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017TIME(3P)

Pages that refer to this page:time.h(0p), touch(1p), asctime(3p), clock(3p), clock_getres(3p), ctime(3p), difftime(3p), fstatvfs(3p), getrusage(3p), gmtime(3p), localtime(3p), mktime(3p), mq_receive(3p), mq_send(3p), posix_trace_create(3p), pthread_mutex_timedlock(3p), sem_timedwait(3p), strftime(3p), strptime(3p), times(3p)