Page 511 - Beginning PHP 5.3

Chapter 16: PHP and the Outside World
If, when using any of PHP ’ s date - related functions, you get an error message telling you that it is not
safe to rely on the system ’ s time zone settings, you need to configure PHP ’ s time zone. See the “ Setting
Your Time Zone ” section in Chapter 2 for instructions.

Creating Your Own Timestamps

Although time() is useful for getting the current time, often you want to work with other dates and
times. You can use various PHP functions to create timestamps for storing dates and times. The three
that you ’ re likely to use most often are mktime() , gmmktime() , and strtotime() .

Creating Timestamps from Date and Time Values
The mktime() function returns a timestamp based on up to six time/date arguments, as follows:
❑ Hour (0 – 23)
❑ Minute (0 – 59)
❑ Second (0 – 59)

❑ Month (1 – 12)
❑ Day of the month (1 – 31)
❑ Year (1901 – 2038)

For example, the following code displays the timestamp corresponding to 2:32:12 pm on January 6, 1972:
echo mktime( 14, 32, 12, 1, 6, 1972 );

You can leave out as many arguments as you like, and the value corresponding to the current time will
be used instead. For example, if the current date is December 22, 2008, the following code displays the
timestamp representing 10 am on December 22, 2008:

echo mktime( 10, 0, 0 );
If you omit all the arguments, mktime() returns the current date and time, just like time() .
Incidentally, you can pass in arguments that are outside the allowed ranges, and mktime() adjusts the
values accordingly. So passing in a value of 3 for the month and 32 for the day causes mktime() to
return a timestamp representing April 1.
Creating Timestamps from GMT Date and Time Values
mktime() assumes that the arguments you pass are in your computer ’ s time zone — it converts the
supplied time to UTC so that it can be returned as a timestamp. However, sometimes it ’ s useful to be
able to store a date and time that ’ s already in the GMT time zone. For example, many HTTP headers and
other TCP/IP protocols work with dates and times that are always in GMT.

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