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<HTML
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>class</TITLE
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>PHP Manual</TH
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>Chapter 11. Control Structures</TD
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="KEYWORD.CLASS"
><TT
CLASS="LITERAL"
>class</TT
></A
></H1
><P
>     A class is a collection of variables and functions working with
     these variables.  A class is defined using the following syntax:
 
     <DIV
CLASS="INFORMALEXAMPLE"
><P
></P
><PRE
CLASS="PROGRAMLISTING"
> &lt;?php
 class Cart {
     var $items;  // Items in our shopping cart
   
     // Add $num articles of $artnr to the cart
 
     function add_item ($artnr, $num) {
         $this-&#62;items[$artnr] += $num;
     }
   
     // Take $num articles of $artnr out of the cart
 
     function remove_item ($artnr, $num) {
         if ($this-&#62;items[$artnr] &#62; $num) {
             $this-&#62;items[$artnr] -= $num;
             return true;
         } else {
             return false;
         }   
     }
 }
 ?&#62;
      </PRE
><P
></P
></DIV
>
 
    </P
><P
>     This defines a class named Cart that consists of an associative
     array of articles in the cart and two functions to add and remove
     items from this cart.
 
    </P
><P
>     Classes are types, that is, they are blueprints for actual
     variables. You have to create a variables of the desired type with
     the new operator.
    </P
><DIV
CLASS="INFORMALEXAMPLE"
><P
></P
><PRE
CLASS="PROGRAMLISTING"
> $cart = new Cart;
 $cart-&#62;add_item("10", 1);
     </PRE
><P
></P
></DIV
><P
>     This creates an object $cart of the class Cart. The function
     add_item() of that object is being called to add 1 item of article
     number 10 to the cart.
    </P
><P
>     Classes can be extensions of other classes. The extended or
     derived class has all variables and functions of the base class
     and what you add in the extended definition.  This is done using
     the extends keyword.
    </P
><DIV
CLASS="INFORMALEXAMPLE"
><P
></P
><PRE
CLASS="PROGRAMLISTING"
> class Named_Cart extends Cart {
     var $owner;
  
     function set_owner ($name) {
         $this-&#62;owner = $name;
     }
 }
     </PRE
><P
></P
></DIV
><P
>     This defines a class Named_Cart that has all variables and
     functions of Cart plus an additional variable $owner and an
     additional function set_owner(). You create a named cart the usual
     way and can now set and get the carts owner. You can still use
     normal cart functions on named carts:
    </P
><DIV
CLASS="INFORMALEXAMPLE"
><P
></P
><PRE
CLASS="PROGRAMLISTING"
> $ncart = new Named_Cart;    // Create a named cart
 $ncart-&#62;set_owner ("kris"); // Name that cart
 print $ncart-&#62;owner;        // print the cart owners name
 $ncart-&#62;add_item ("10", 1); // (inherited functionality from cart)
     </PRE
><P
></P
></DIV
><P
>     Within functions of a class the variable $this means this
     object. You have to use $this-&#62;something to access any variable or
     function named something within your current object.
    </P
><P
>     Constructors are functions in a class that are automatically 
     called when you create a new instance of a class. A function 
     becomes a constructor when it has the same name as the class.
    </P
><DIV
CLASS="INFORMALEXAMPLE"
><P
></P
><PRE
CLASS="PROGRAMLISTING"
> class Auto_Cart extends Cart {
     function Auto_Cart () {
         $this-&#62;add_item ("10", 1);
     }
 }
     </PRE
><P
></P
></DIV
><P
>     This defines a class Auto_Cart that is a Cart plus a constructor
     which initializes the cart with one item of article number "10"
     each time a new Auto_Cart is being made with "new". Constructors
     can also take arguments and these arguments can be optional, which
     makes them much more useful.
    </P
><DIV
CLASS="INFORMALEXAMPLE"
><P
></P
><PRE
CLASS="PROGRAMLISTING"
> class Constructor_Cart {
     function Constructor_Cart ($item = "10", $num = 1) {
         $this-&#62;add_item ($item, $num);
     }
 }
 
 // Shop the same old boring stuff.
 
 $default_cart   = new Constructor_Cart;
 
 // Shop for real...
 
 $different_cart = new Constructor_Cart ("20", 17);
     </PRE
><P
></P
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><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
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><P
>      For derived classes, the constructor of the parent class is not
      automatically called when the derived class's constructor is called.
    </P
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