Sophie: php-manual-en-4.3.0-2mdk noarch

php-manual-en-4.3.0-2mdk.noarch.rpm

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><DIV
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><H1
><A
NAME="language.oop"
>Chapter 14. Classes and Objects</A
></H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="language.oop.html#keyword.class"
><TT
CLASS="literal"
>class</TT
></A
></DT
><DT
><A
HREF="keyword.extends.html"
><TT
CLASS="literal"
>extends</TT
></A
></DT
><DT
><A
HREF="language.oop.constructor.html"
><TT
CLASS="literal"
>Constructors</TT
></A
></DT
><DT
><A
HREF="keyword.paamayim-nekudotayim.html"
><TT
CLASS="literal"
>::</TT
></A
></DT
><DT
><A
HREF="keyword.parent.html"
><TT
CLASS="literal"
>parent</TT
></A
></DT
><DT
><A
HREF="language.oop.serialization.html"
>Serializing objects - objects in sessions</A
></DT
><DT
><A
HREF="language.oop.magic-functions.html"
>The magic functions <TT
CLASS="literal"
>__sleep</TT
> and <TT
CLASS="literal"
>__wakeup</TT
></A
></DT
><DT
><A
HREF="language.oop.newref.html"
>References inside the constructor</A
></DT
></DL
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="keyword.class"
></A
><TT
CLASS="literal"
>class</TT
></H1
><P
>&#13;    A class is a collection of variables and functions working with
    these variables.  A class is defined using the following syntax:
 
    <DIV
CLASS="informalexample"
><A
NAME="AEN5433"
></A
><P
></P
><TABLE
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><TR
><TD
><PRE
CLASS="php"
>&#60;?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
></TD
></TR
></TABLE
><P
></P
></DIV
>
   </P
><P
>&#13;    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
><DIV
CLASS="caution"
><P
></P
><TABLE
CLASS="caution"
BORDER="1"
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><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
>&#13;     The following cautionary notes are valid for PHP 4.
    </P
><P
>&#13;     The name <TT
CLASS="literal"
>stdClass</TT
> is used interally by
     Zend and is reserved. You cannot have a class named
     <TT
CLASS="literal"
>stdClass</TT
> in PHP.
    </P
><P
>&#13;      The function names <TT
CLASS="literal"
>__sleep</TT
> and
      <TT
CLASS="literal"
>__wakeup</TT
> are magical in PHP classes. You
      cannot have functions with these names in any of your
      classes unless you want the magic functionality associated
      with them. See below for more information.
    </P
><P
>&#13;      PHP reserves all function names starting with __ as magical.
      It is recommended that you do not use function names with
      __ in PHP unless you want some documented magic functionality.
    </P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
     In PHP 4, only constant initializers for <TT
CLASS="literal"
>var</TT
>
     variables are allowed. To initialize variables with non-constant
     values, you need an initialization function which is called
     automatically when an object is being constructed from the
     class. Such a function is called a constructor (see below).
    </P
><DIV
CLASS="informalexample"
><A
NAME="AEN5448"
></A
><P
></P
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><TD
><PRE
CLASS="php"
>&#60;?php
/* None of these will work in PHP 4. */
class Cart
{
    var $todays_date = date("Y-m-d");
    var $name = $firstname;
    var $owner = 'Fred ' . 'Jones';
    var $items = array("VCR", "TV");
}

/* This is how it should be done. */
class Cart
{
    var $todays_date;
    var $name;
    var $owner;
    var $items;

    function Cart()
    {
        $this-&#62;todays_date = date("Y-m-d");
        $this-&#62;name = $GLOBALS['firstname'];
        /* etc. . . */
    }
}
?&#62;</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
></BLOCKQUOTE
></DIV
><P
>&#13;    Classes are types, that is, they are blueprints for actual
    variables. You have to create a variable of the desired type with
    the <TT
CLASS="literal"
>new</TT
> operator.
   </P
><DIV
CLASS="informalexample"
><A
NAME="AEN5452"
></A
><P
></P
><TABLE
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><TR
><TD
><PRE
CLASS="php"
>&#60;?php
$cart = new Cart;
$cart-&#62;add_item("10", 1);

$another_cart = new Cart;
$another_cart-&#62;add_item("0815", 3);</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
><P
>&#13;    This creates the objects $cart and $another_cart, both of
    the class Cart. The function add_item() of the $cart object
    is being called to add 1 item of article number 10 to the
    $cart. 3 items of article number 0815 are being added to
    $another_cart.
   </P
><P
>&#13;    Both, $cart and $another_cart, have functions add_item(),
    remove_item() and a variable items. These are distinct
    functions and variables. You can think of the objects as
    something similar to directories in a filesystem. In a
    filesystem you can have two different files README.TXT, as
    long as they are in different directories.  Just like with
    directories where you'll have to type the full pathname in
    order to reach each file from the toplevel directory, you
    have to specify the complete name of the function you want
    to call: In PHP terms, the toplevel directory would be the
    global namespace, and the pathname separator would be -&#62;. 
    Thus, the names $cart-&#62;items and $another_cart-&#62;items
    name two different variables. Note that the variable is
    named $cart-&#62;items, not $cart-&#62;$items, that is, a
    variable name in PHP has only a single dollar sign.
   </P
><DIV
CLASS="informalexample"
><A
NAME="AEN5456"
></A
><P
></P
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><TR
><TD
><PRE
CLASS="php"
>// correct, single $
$cart-&#62;items = array("10" =&#62; 1); 

// invalid, because $cart-&#62;$items becomes $cart-&#62;""
$cart-&#62;$items = array("10" =&#62; 1);

// correct, but may or may not be what was intended:
// $cart-&#62;$myvar becomes $cart-&#62;items
$myvar = 'items';
$cart-&#62;$myvar = array("10" =&#62; 1);</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
><P
>&#13;    Within a class definition, you do not know under which name the object will
    be accessible in your program: at the time the Cart class was 
    written, it was unknown that the object will be named $cart or
    $another_cart later. Thus, you cannot write $cart-&#62;items within
    the Cart class itself. Instead, in order to be able to access it's own
    functions and variables from within a class, one can use the
    pseudo-variable $this which can be read as 'my own' or
    'current object'. Thus, '$this-&#62;items[$artnr] += $num' can
    be read as 'add $num to the $artnr counter of my own items
    array' or 'add $num to the $artnr counter of the items array
    within the current object'.
   </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
    There are some nice functions to handle classes and objects. You might want
    to take a look at the <A
HREF="ref.classobj.html"
>Class/Object
    Functions</A
>
    </P
></BLOCKQUOTE
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