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>Chapter 15. References Explained</TD
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>What References Do</H1
><P
>&#13;    PHP references allow you to make two variables to refer to the
    same content. Meaning, when you do:
    <DIV
CLASS="informalexample"
><A
NAME="AEN5601"
></A
><P
></P
><TABLE
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><TR
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><PRE
CLASS="php"
>$a =&#38; $b</PRE
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>
    it means that <TT
CLASS="varname"
>$a</TT
> and <TT
CLASS="varname"
>$b</TT
>
    point to the same variable.
    <DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
      <TT
CLASS="varname"
>$a</TT
> and <TT
CLASS="varname"
>$b</TT
> are completely
      equal here, that's not <TT
CLASS="varname"
>$a</TT
> is pointing to
      <TT
CLASS="varname"
>$b</TT
> or vice versa, that's
      <TT
CLASS="varname"
>$a</TT
> and <TT
CLASS="varname"
>$b</TT
> pointing to the
      same place.
     </P
></BLOCKQUOTE
></DIV
>
   </P
><P
>&#13;   The same syntax can be used with functions, that return references,
   and with <TT
CLASS="literal"
>new</TT
> operator (in PHP 4.0.4 and later):
    <DIV
CLASS="informalexample"
><A
NAME="AEN5615"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
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><TR
><TD
><PRE
CLASS="php"
>$bar =&#38; new fooclass();
$foo =&#38; find_var ($bar);</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    </P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>
     Not using the <TT
CLASS="literal"
>&#38;</TT
> operator causes a copy of the
     object to be made. If you use <TT
CLASS="literal"
>$this</TT
> in the class it
     will operate on the current instance of the class. The assignment without
     <TT
CLASS="literal"
>&#38;</TT
> will copy the instance (i.e. the object) and
     <TT
CLASS="literal"
>$this</TT
> will operate on the copy, which is not always
     what is desired. Usually you want to have a single instance to work with,
     due to performance and memory consumption issues.
     </P
><P
>&#13;      While you can use the <TT
CLASS="literal"
>@</TT
> operator to
      <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>mute</I
></SPAN
> any errors in the constructor when using it as
      <TT
CLASS="literal"
>@new</TT
>, this does not work when using the
      <TT
CLASS="literal"
>&#38;new</TT
> statement. This is a limitation of the Zend
      Engine and will therefore result in a parser error.
     </P
></BLOCKQUOTE
></DIV
><P
>&#13;    The second thing references do is to pass variables
    by-reference. This is done by making a local variable in a function and
    a variable in the calling scope reference to the same content. Example:
    <DIV
CLASS="informalexample"
><A
NAME="AEN5629"
></A
><P
></P
><TABLE
BORDER="0"
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><TR
><TD
><PRE
CLASS="php"
>function foo (&#38;$var)
{
    $var++;
}

$a=5;
foo ($a);</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    will make <TT
CLASS="varname"
>$a</TT
> to be 6. This happens because in
    the function <TT
CLASS="varname"
>foo</TT
> the variable
    <TT
CLASS="varname"
>$var</TT
> refers to the same content as
    <TT
CLASS="varname"
>$a</TT
>. See also more detailed explanations about <A
HREF="language.references.pass.html"
>passing by reference</A
>.
   </P
><P
>&#13;    The third thing reference can do is <A
HREF="language.references.return.html"
>return by reference</A
>.
   </P
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