PHP Functions

Jussi Pohjolainen

Tampere University of Applied Sciences

Intro to php functions

• PHP has lots of predefined functions. [See list]
• For example: $date_str = date("m.d.y");
• It is possible to create your own functions.
• Each function should perform a single simple task

Function example

• All functions start with the word function()
• Every function has a name. Give a name that describes the function
• Function starts with "{" and ends with "}"
• Example

  function say_hello()
  {
      print "Hello!";
  }
  

• Usage:

say_hello();

Parameters

• Adding parameters is easy. Parameter is a variable which value is given in a function call.
• Example:

  function say_hello($name)
  {
      print "Hello! " . $name;
  }
  

• Usage:

say_hello("Jack Bauer");

More Parameters

• You can have as many parameters as you want.
• Example:

  function say_hello($name, $amount)
  {
      for($i=0; $i<$amount; $i++)
      {
          print "Hello! " . $name . "\n";
      }
  }
  

• Usage:

say_hello("Jack Bauer", 12);

Default parameters

• It's possible to give a default value to a parameter
• Example:

  function say_hello($name, $amount=1)
  {
      for($i=0; $i<$amount; $i++)
      {
          print "Hello! " . $name . "\n";
      }
  }
  

• Usage:

say_hello("Jack Bauer");

say_hello("Jack Bauer", 12);

Reference arguments

• By default all the arguments are passed by value.
• If you want to pass the argument by reference use & in front of the argument
• Example:

  function do_something(&$variable)
  {
      $variable++;
  }
  

• Example:

  function &do_something()
  {
      ...
         return $variable;
  }
  

Function return values

• Functions can also be used to return values.
• Example:

  function hello($name, $amount=1)
  {
      $greeting = "";
      for($i=0; $i<$amount; $i++)
      {
          $greeting = $greeting . "Hello! " . $name . "\n";
      }
      return $greeting;
  }
  

• Usage:

$text = hello("Jack Bauer", 12);

Commenting functions

• It is wise to comment every function
• Use PhpDocumentor coding style, see example
• Example:

  
  /**
  * Checks if given string is valid e-mail address
  *
  * @param string $email address that is needs to be checked
  * @return bool true if $email is valid e-mail address, false if it's not.
  */
  function check_email($email)
  {
      ...
  }
  

Namespacing

• Namespacing is critical in large code base.
• PHP does not have real namespaces.. use classes instead.
• Classes can have static and non-static methods. If class holds only static methods, you can think that the class is like a namespace

Namespacing example

• class CheckInput
  {
      public static function check_email($email)
      {
      }
      public static function check_age($age)
      {
      }
  }    
  

• Usage: CheckInput::check_email(...);

Dividing code

• Try to separate GUI (html) and BL (Business logic) from each other
• Simple way is to use functions. Put as much as logic you can in to functions and call them from GUI. This way the code is much easier to read and maintain.
• See bad- vs. good-examples.

Intro to OO (Object-orientated) programming

• The biggest change in PHP 5 is the support for OO-techniques
• Traditional way of programming in PHP is to use procedural programming concepts
• When the software project gets large, it's recommerend to use OO-techniques
• OO-programming holds many concepts: class, object, inheritance, encapsulation, methods, polymorphism
• See OO-example