How do you create optional arguments in php?

In the php manual they describe functions like so:

string date ( string $format [, int $timestamp ] )

How would this function look when you define it?

From stackoverflow ghostz00

• function dosomething($var1, $var2, $var3='somevalue'){
  ..
  }
  

  From Jeff Winkworth

• Give the optional argument a default value.

  function date ($format, $timestamp='') {
  }
  

  From mk

• Some notes that I also found useful:

  • Keep your default values on the right side.

    function whatever($var1, $var2, $var3="constant", $var4="another")

  • The default value of the argument must be a constant expression. It can't be a variable or a function call.

  From ghostz00

• The default value of the argument must be a constant expression. It can't be a variable or a function call.

  If you need this functionality however:

  function foo($foo, $bar = false)
  {
      if(!$bar)
      {
          $bar = $foo;
      }
  }
  

  Assuming $bar isn't expected to be a boolean of course.

  From Ross