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><H1
><A
NAME="language.oop"
>Cap. 13. Classes and Objects (PHP 4)</A
></H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Cuprins</B
></DT
><DT
><A
HREF="language.oop.html#keyword.class"
><VAR
CLASS="literal"
>class</VAR
></A
></DT
><DT
><A
HREF="keyword.extends.html"
><VAR
CLASS="literal"
>extends</VAR
></A
></DT
><DT
><A
HREF="language.oop.constructor.html"
><VAR
CLASS="literal"
>Constructors</VAR
></A
></DT
><DT
><A
HREF="keyword.paamayim-nekudotayim.html"
><VAR
CLASS="literal"
>::</VAR
></A
></DT
><DT
><A
HREF="keyword.parent.html"
><VAR
CLASS="literal"
>parent</VAR
></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 <VAR
CLASS="literal"
>__sleep</VAR
> and <VAR
CLASS="literal"
>__wakeup</VAR
></A
></DT
><DT
><A
HREF="language.oop.newref.html"
>References inside the constructor</A
></DT
><DT
><A
HREF="language.oop.object-comparison.html"
>Comparing objects</A
></DT
></DL
></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="keyword.class"
><VAR
CLASS="literal"
>class</VAR
></A
></H1
><P
> A class is a collection of variables and functions working with
these variables. A class is defined using the following syntax:
</P
><P
> <DIV
CLASS="informalexample"
><P
></P
><A
NAME="AEN3129"
></A
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#007700">class </font><font color="#0000BB">Cart </font><font color="#007700">{<br /> var </font><font color="#0000BB">$items</font><font color="#007700">; </font><font color="#FF8000">// Items in our shopping cart<br /> <br /> // Add $num articles of $artnr to the cart<br /> <br /> </font><font color="#007700">function </font><font color="#0000BB">add_item</font><font color="#007700">(</font><font color="#0000BB">$artnr</font><font color="#007700">, </font><font color="#0000BB">$num</font><font color="#007700">) {<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">items</font><font color="#007700">[</font><font color="#0000BB">$artnr</font><font color="#007700">] += </font><font color="#0000BB">$num</font><font color="#007700">;<br /> }<br /> <br /> </font><font color="#FF8000">// Take $num articles of $artnr out of the cart<br /> <br /> </font><font color="#007700">function </font><font color="#0000BB">remove_item</font><font color="#007700">(</font><font color="#0000BB">$artnr</font><font color="#007700">, </font><font color="#0000BB">$num</font><font color="#007700">) {<br /> if (</font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">items</font><font color="#007700">[</font><font color="#0000BB">$artnr</font><font color="#007700">] > </font><font color="#0000BB">$num</font><font color="#007700">) {<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">items</font><font color="#007700">[</font><font color="#0000BB">$artnr</font><font color="#007700">] -= </font><font color="#0000BB">$num</font><font color="#007700">;<br /> return </font><font color="#0000BB">true</font><font color="#007700">;<br /> } else {<br /> return </font><font color="#0000BB">false</font><font color="#007700">;<br /> } <br /> }<br />}<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><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
><DIV
CLASS="warning"
><P
></P
><TABLE
CLASS="warning"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Avertisment</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> You can <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>NOT</I
></SPAN
> break up a class definition into
multiple files, or multiple PHP blocks. The following will not work:
</P
><P
> <DIV
CLASS="informalexample"
><P
></P
><A
NAME="AEN3136"
></A
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#007700">class </font><font color="#0000BB">test </font><font color="#007700">{<br /></font><font color="#0000BB">?><br /><?php<br /> </font><font color="#007700">function </font><font color="#0000BB">test</font><font color="#007700">() {<br /> print </font><font color="#DD0000">'OK'</font><font color="#007700">;<br /> }<br />}<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><P
></P
></DIV
>
</P
></TD
></TR
></TABLE
></DIV
><P
> The following cautionary notes are valid for PHP 4.
</P
><DIV
CLASS="caution"
><P
></P
><TABLE
CLASS="caution"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Atenþie</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> The name <VAR
CLASS="literal"
>stdClass</VAR
> is used interally by
Zend and is reserved. You cannot have a class named
<VAR
CLASS="literal"
>stdClass</VAR
> in PHP.
</P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="caution"
><P
></P
><TABLE
CLASS="caution"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Atenþie</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> The function names <VAR
CLASS="literal"
>__sleep</VAR
> and
<VAR
CLASS="literal"
>__wakeup</VAR
> 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
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="caution"
><P
></P
><TABLE
CLASS="caution"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
>Atenþie</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
> 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
><P
> In PHP 4, only constant initializers for <VAR
CLASS="literal"
>var</VAR
>
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"
><P
></P
><A
NAME="AEN3151"
></A
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#007700">class </font><font color="#0000BB">Cart </font><font color="#007700">{<br /> </font><font color="#FF8000">/* None of these will work in PHP 4. */<br /> </font><font color="#007700">var </font><font color="#0000BB">$todays_date </font><font color="#007700">= </font><font color="#0000BB">date</font><font color="#007700">(</font><font color="#DD0000">"Y-m-d"</font><font color="#007700">);<br /> var </font><font color="#0000BB">$name </font><font color="#007700">= </font><font color="#0000BB">$firstname</font><font color="#007700">;<br /> var </font><font color="#0000BB">$owner </font><font color="#007700">= </font><font color="#DD0000">'Fred ' </font><font color="#007700">. </font><font color="#DD0000">'Jones'</font><font color="#007700">;<br /> </font><font color="#FF8000">/* Arrays containing constant values will, though. */<br /> </font><font color="#007700">var </font><font color="#0000BB">$items </font><font color="#007700">= array(</font><font color="#DD0000">"VCR"</font><font color="#007700">, </font><font color="#DD0000">"TV"</font><font color="#007700">);<br />}<br /><br /></font><font color="#FF8000">/* This is how it should be done. */<br /></font><font color="#007700">class </font><font color="#0000BB">Cart </font><font color="#007700">{<br /> var </font><font color="#0000BB">$todays_date</font><font color="#007700">;<br /> var </font><font color="#0000BB">$name</font><font color="#007700">;<br /> var </font><font color="#0000BB">$owner</font><font color="#007700">;<br /> var </font><font color="#0000BB">$items </font><font color="#007700">= array(</font><font color="#DD0000">"VCR"</font><font color="#007700">, </font><font color="#DD0000">"TV"</font><font color="#007700">);<br /><br /> function </font><font color="#0000BB">Cart</font><font color="#007700">() {<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">todays_date </font><font color="#007700">= </font><font color="#0000BB">date</font><font color="#007700">(</font><font color="#DD0000">"Y-m-d"</font><font color="#007700">);<br /> </font><font color="#0000BB">$this</font><font color="#007700">-></font><font color="#0000BB">name </font><font color="#007700">= </font><font color="#0000BB">$GLOBALS</font><font color="#007700">[</font><font color="#DD0000">'firstname'</font><font color="#007700">];<br /> </font><font color="#FF8000">/* etc. . . */<br /> </font><font color="#007700">}<br />}<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><P
></P
></DIV
><P
> Classes are types, that is, they are blueprints for actual
variables. You have to create a variable of the desired type with
the <VAR
CLASS="literal"
>new</VAR
> operator.
</P
><DIV
CLASS="informalexample"
><P
></P
><A
NAME="AEN3155"
></A
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br />$cart </font><font color="#007700">= new </font><font color="#0000BB">Cart</font><font color="#007700">;<br /></font><font color="#0000BB">$cart</font><font color="#007700">-></font><font color="#0000BB">add_item</font><font color="#007700">(</font><font color="#DD0000">"10"</font><font color="#007700">, </font><font color="#0000BB">1</font><font color="#007700">);<br /><br /></font><font color="#0000BB">$another_cart </font><font color="#007700">= new </font><font color="#0000BB">Cart</font><font color="#007700">;<br /></font><font color="#0000BB">$another_cart</font><font color="#007700">-></font><font color="#0000BB">add_item</font><font color="#007700">(</font><font color="#DD0000">"0815"</font><font color="#007700">, </font><font color="#0000BB">3</font><font color="#007700">);<br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><P
></P
></DIV
><P
> This creates the objects <VAR
CLASS="varname"
>$cart</VAR
> and
<VAR
CLASS="varname"
>$another_cart</VAR
>, both of the class Cart. The function
add_item() of the <VAR
CLASS="varname"
>$cart</VAR
> object is being called to add 1
item of article number 10 to the <VAR
CLASS="varname"
>$cart</VAR
>. 3 items of
article number 0815 are being added to <VAR
CLASS="varname"
>$another_cart</VAR
>.
</P
><P
> Both, <VAR
CLASS="varname"
>$cart</VAR
> and <VAR
CLASS="varname"
>$another_cart</VAR
>, 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 <TT
CLASS="filename"
>README.TXT</TT
>, 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 <VAR
CLASS="literal"
>-></VAR
>. Thus, the names
<VAR
CLASS="varname"
>$cart->items</VAR
> and
<VAR
CLASS="varname"
>$another_cart->items</VAR
> name two different variables.
Note that the variable is named <VAR
CLASS="varname"
>$cart->items</VAR
>, not
<VAR
CLASS="varname"
>$cart->$items</VAR
>, that is, a variable name in PHP has
only a single dollar sign.
</P
><DIV
CLASS="informalexample"
><P
></P
><A
NAME="AEN3172"
></A
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><code><font color="#000000">
<font color="#0000BB"><?php<br /></font><font color="#FF8000">// correct, single $<br /></font><font color="#0000BB">$cart</font><font color="#007700">-></font><font color="#0000BB">items </font><font color="#007700">= array(</font><font color="#DD0000">"10" </font><font color="#007700">=> </font><font color="#0000BB">1</font><font color="#007700">); <br /><br /></font><font color="#FF8000">// invalid, because $cart->$items becomes $cart->""<br /></font><font color="#0000BB">$cart</font><font color="#007700">-></font><font color="#0000BB">$items </font><font color="#007700">= array(</font><font color="#DD0000">"10" </font><font color="#007700">=> </font><font color="#0000BB">1</font><font color="#007700">);<br /><br /></font><font color="#FF8000">// correct, but may or may not be what was intended:<br />// $cart->$myvar becomes $cart->items<br /></font><font color="#0000BB">$myvar </font><font color="#007700">= </font><font color="#DD0000">'items'</font><font color="#007700">;<br /></font><font color="#0000BB">$cart</font><font color="#007700">-></font><font color="#0000BB">$myvar </font><font color="#007700">= array(</font><font color="#DD0000">"10" </font><font color="#007700">=> </font><font color="#0000BB">1</font><font color="#007700">); <br /></font><font color="#0000BB">?></font>
</font>
</code></TD
></TR
></TABLE
><P
></P
></DIV
><P
> 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
<VAR
CLASS="varname"
>$cart</VAR
> or <VAR
CLASS="varname"
>$another_cart</VAR
> later. Thus,
you cannot write <VAR
CLASS="varname"
>$cart->items</VAR
> within the Cart class
itself. Instead, in order to be able to access it's own functions and
variables from within a class, one can use the pseudo-variable
<VAR
CLASS="varname"
>$this</VAR
> which can be read as 'my own' or 'current
object'. Thus, '<VAR
CLASS="varname"
>$this->items[$artnr]</VAR
> +=
<VAR
CLASS="varname"
>$num</VAR
>' can be read as 'add <VAR
CLASS="varname"
>$num</VAR
> to
the <VAR
CLASS="varname"
>$artnr</VAR
> counter of my own items array' or 'add
<VAR
CLASS="varname"
>$num</VAR
> to the <VAR
CLASS="varname"
>$artnr</VAR
> counter of the
items array within the current object'.
</P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Notã: </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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