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3.3. Converting Time and Date Parts to an Epoch Timestamp

3.3.3. Discussion

The functions mktime( ) and gmmktime( ) each take a date and time's parts (hour, minute, second, month, day, year, DST flag) and return the appropriate Unix epoch timestamp. The components are treated as local time by mktime( ), while gmmktime( ) treats them as a date and time in UTC. For both functions, a seventh argument, the DST flag (1 if DST is being observed, 0 if not), is optional. These functions return sensible results only for times within the epoch. Most systems store epoch timestamps in a 32-bit signed integer, so "within the epoch" means between 8:45:51 P.M. December 13, 1901 UTC and 3:14:07 A.M. January 19, 2038 UTC.

In the following example, $stamp_now is the epoch timestamp when mktime( ) is called and $stamp_future is the epoch timestamp for 3:25 P.M. on June 4, 2012:

$stamp_now = mktime( );
$stamp_future = mktime(15,25,0,6,4,2012);

print $stamp_now;
print $stamp_future;

Both epoch timestamps can be fed back to strftime( ) to produce formatted time strings:

print strftime('%c',$stamp_now);
print strftime('%c',$stamp_future);
Thu Aug  8 00:53:41 2002
Mon Jun 4 15:25:00 2012

Because the previous calls to mktime( ) were made on a computer set to EDT (which is four hours behind GMT), using gmmktime( ) instead produces epoch timestamps that are 14400 seconds (four hours) smaller:

$stamp_now = gmmktime( );
$stamp_future = gmmktime(15,25,0,6,4,2012);

print $stamp_now;
print $stamp_future;

Feeding these gmmktime( )-generated epoch timestamps back to strftime( ) produces formatting time strings that are also four hours earlier:

print strftime('%c',$stamp_now);
print strftime('%c',$stamp_future);
Wed Aug  7 20:53:41 2002
Mon Jun 4 11:25:00 2012

3.3.4. See Also

Recipe 3.4 for how to convert an epoch timestamp back to time and date parts; documentation on mktime( ) at http://www.php.net/mktime and gmmktime( ) at http://www.php.net/gmmktime.

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