PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

478 Chapter 21 Managing the Date and Time
Listing 21.1
$year = 1972;
Continued
// remember you need bday as day month and year
$bdayunix = mktime (0, 0, 0, $month, $day, $year); // get ts for then
$nowunix = time(); // get unix ts for today
$ageunix = $nowunix - $bdayunix; // work out the difference
$age = floor($ageunix / (365 * 24 * 60 * 60)); // convert from seconds to years
echo “Age is $age”;
?>
This script sets the date for calculating the age. In a real application, it is likely that this
information might come from an HTML form.The script begins by calling mktime() to
work out the timestamp for the birthday and for the current time:
$bdayunix = mktime (0, 0, 0, $month, $day, $year);
$nowunix = time(); // get unix ts for today
Now that these dates are in the same format, you can simply subtract them:
$ageunix = $nowunix - $bdayunix;
Now, the slightly tricky part: converting this time period back to a more human-friendly
unit of measure.This is not a timestamp but instead the age of the person measured in
seconds.You can convert it back to years by dividing by the number of seconds in a year.
You then round it down by using the floor() function because a person is not said to
be, for example, 20, until the end of his twentieth year:
$age = floor($ageunix / (365 * 24 * 60 * 60)); // convert from seconds to years
Note, however, that this approach is somewhat flawed because it is limited by the range
of Unix timestamps (generally 32-bit integers). Birthdates are not an ideal application
for timestamps.This example works on all platforms only for people born from 1970
onward.Windows cannot manage timestamps prior to 1970. Even then, this calculation
is not always accurate because it does not allow for leap years and might fail if midnight
on the person’s birthday is the daylight savings switchover time in the local time zone.
Calculating Dates in MySQL
PHP does not have many date manipulation functions built in. Obviously, you can write
your own, but ensuring that you correctly account for leap years and daylight savings time
can be tricky.Another option is to download other people’s functions.You can find many as
user-contributed notes in the PHP manual, but only some of them are well thought out.
Note
Several date calculation functions have been added to PHP 5.3, including date_add(), date_sub(),
and date_diff() among others. These date manipulation functions eliminate having to use MySQL to
provide the easy date manipulation that PHP previously lacked.