PHP why is not "strtotime is not defined"

// why does this not work PHP in XAMMP stack
// error: "strtotime is not def开发者_StackOverflow中文版ined"

$date2 = strtotime('2010-10-01');

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According to http://us3.php.net/manual/en/calendar.installation.php,

To get these functions to work, you have to compile PHP with --enable-calendar.

The Windows version of PHP has built-in support for this extension. You do not need to load any additional extensions in order to use these functions.

or on OS X:

sudo port install php5-calendar

Failing that, try looking for php5-calendar in your system's package manager.