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<h2 class="title">Passing by Reference</h2>
<p class="para">
You can pass a variable by reference to a function so the function
can modify the variable. The syntax is as follows:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">foo</span><span style="color: #007700">(&</span><span style="color: #0000BB">$var</span><span style="color: #007700">)<br />{<br /> </span><span style="color: #0000BB">$var</span><span style="color: #007700">++;<br />}<br /><br /></span><span style="color: #0000BB">$a</span><span style="color: #007700">=</span><span style="color: #0000BB">5</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">(</span><span style="color: #0000BB">$a</span><span style="color: #007700">);<br /></span><span style="color: #FF8000">// $a is 6 here<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
There is no reference sign on a function call - only on
function definitions. Function definitions alone are enough to
correctly pass the argument by reference. As of PHP 5.3.0,
you will get a warning saying that "call-time pass-by-reference" is
deprecated when you use & in <em>foo(&$a);</em>.
And as of PHP 5.4.0, call-time pass-by-reference was removed, so
using it will raise a fatal error.
</span>
</p></blockquote>
</p>
<p class="para">
The following things can be passed by reference:
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
Variables, i.e. <em>foo($a)</em>
</span>
</li>
<li class="listitem">
<span class="simpara">
New statements, i.e. <em>foo(new foobar())</em>
</span>
</li>
<li class="listitem">
<p class="para">
References returned from functions, i.e.:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">foo</span><span style="color: #007700">(&</span><span style="color: #0000BB">$var</span><span style="color: #007700">)<br />{<br /> </span><span style="color: #0000BB">$var</span><span style="color: #007700">++;<br />}<br />function &</span><span style="color: #0000BB">bar</span><span style="color: #007700">()<br />{<br /> </span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">5</span><span style="color: #007700">;<br /> return </span><span style="color: #0000BB">$a</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">(</span><span style="color: #0000BB">bar</span><span style="color: #007700">());<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
See more about <a href="language.references.return.html" class="link">returning by reference</a>.
</p>
</li>
</ul>
</p>
<p class="para">
No other expressions should be passed by reference, as the
result is undefined. For example, the following examples of passing
by reference are invalid:
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">foo</span><span style="color: #007700">(&</span><span style="color: #0000BB">$var</span><span style="color: #007700">)<br />{<br /> </span><span style="color: #0000BB">$var</span><span style="color: #007700">++;<br />}<br />function </span><span style="color: #0000BB">bar</span><span style="color: #007700">() </span><span style="color: #FF8000">// Note the missing &<br /></span><span style="color: #007700">{<br /> </span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">5</span><span style="color: #007700">;<br /> return </span><span style="color: #0000BB">$a</span><span style="color: #007700">;<br />}<br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">(</span><span style="color: #0000BB">bar</span><span style="color: #007700">()); </span><span style="color: #FF8000">// Produces fatal error since PHP 5.0.5<br /><br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">(</span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">5</span><span style="color: #007700">); </span><span style="color: #FF8000">// Expression, not variable<br /></span><span style="color: #0000BB">foo</span><span style="color: #007700">(</span><span style="color: #0000BB">5</span><span style="color: #007700">); </span><span style="color: #FF8000">// Produces fatal error<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
These requirements are for PHP 4.0.4 and later.
</p>
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