Page 512 - Beginning PHP 5.3

Part III: Using PHP in Practice
To create a timestamp from a GMT date and time, use gmmktime() . This works in exactly the same way
as mktime() , except that it expects its arguments to be in GMT. For example, let ’ s say the computer
running your PHP script is in the Indianapolis time zone, which is 5 hours behind GMT, and that it is
running the following code:

$localTime = mktime( 14, 32, 12, 1, 6, 1972 );
$gmTime = gmmktime( 14, 32, 12, 1, 6, 1972 );

After this code has run, $localTime holds the timestamp representing Jan 6, 1972 at 7:32:12 pm GMT/
UTC (which is 2:32 pm on the same day Indianapolis time). Meanwhile, $gmtime holds the timestamp
for 2:32:12 pm GMT/UTC; in other words, no time zone conversion has taken place.

mktime() and other date - related functions use the time zone set by the date.timezone directive in
the php.ini file (see Chapter 2 for details). However you can, if desired, change the time zone used by
your PHP script with the date_default_timezone_set() function. See the PHP manual at
http://www.php.net/date_default_timezone_set for more details on this function.

Creating Timestamps from Date and Time Strings
mktime() is great if you already have the individual numeric values for the date and time you want to store.
However, often your PHP script will receive a date or time as a string. For example, if your script works with
emails, it may need to handle message dates, which are normally represented in the following format:

Date: Mon, 22 Dec 2008 02:30:17 +0000

Web server logs tend to use a format such as the following:
15/Dec/2008:20:33:30 +1100

Alternatively, your script might receive a user - input date along the lines of:

15th September 2006 3:12pm
Although you can use PHP ’ s powerful string manipulation functions (see Chapter 5) and regular
expressions (see Chapter 18) to split such strings into their component parts for feeding to mktime() ,
PHP provides a useful function called strtotime() to do the hard work for you. strtotime() expects
a string representing a date, and attempts to convert the string into a timestamp:

$timestamp = strtotime( “15th September 2006 3:12pm” );
You can pass in dates and times in practically any human - readable format you like. Here are some
examples of valid date/time strings that you can pass to strtotime() :

Date/Time String Meaning
6/18/99 3:12:28pm 3:12:28 pm on June 18 , 1999
th
th
15th Feb 04 9:30am 9:30 am on February 15 , 2004
th
February 15th 2004, 9:30am 9:30 am on February 15 , 2004

474

9/21/09 9:15:27 AM
c16.indd 474 9/21/09 9:15:27 AM
c16.indd 474