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<title>Dumps a string representation of an internal zend value to output</title>
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</div><hr /><div id="function.debug-zval-dump" class="refentry">
<div class="refnamediv">
<h1 class="refname">debug_zval_dump</h1>
<p class="verinfo">(PHP 4 >= 4.2.0, PHP 5)</p><p class="refpurpose"><span class="refname">debug_zval_dump</span> — <span class="dc-title">Dumps a string representation of an internal zend value to output</span></p>
</div>
<div class="refsect1 description" id="refsect1-function.debug-zval-dump-description">
<h3 class="title">Description</h3>
<div class="methodsynopsis dc-description">
<span class="type"><span class="type void">void</span></span> <span class="methodname"><strong>debug_zval_dump</strong></span>
( <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$variable</code></span>
[, <span class="methodparam"><span class="type"><a href="language.pseudo-types.html#language.types.mixed" class="type mixed">mixed</a></span> <code class="parameter">$...</code></span>
] )</div>
<p class="para rdfs-comment">
Dumps a string representation of an internal zend value to output.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-function.debug-zval-dump-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term"><em><code class="parameter">variable</code></em></span>
<dd>
<p class="para">
The variable being evaluated.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-function.debug-zval-dump-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
No value is returned.
</p>
</div>
<div class="refsect1 examples" id="refsect1-function.debug-zval-dump-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-5244">
<p><strong>Example #1 <span class="function"><strong>debug_zval_dump()</strong></span> example</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$var1 </span><span style="color: #007700">= </span><span style="color: #DD0000">'Hello World'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$var2 </span><span style="color: #007700">= </span><span style="color: #DD0000">''</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$var2 </span><span style="color: #007700">=& </span><span style="color: #0000BB">$var1</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">debug_zval_dump</span><span style="color: #007700">(&</span><span style="color: #0000BB">$var1</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>The above example will output:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
&string(11) "Hello World" refcount(3)
</pre></div>
</div>
</div>
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<strong>Beware the <em>refcount</em></strong><br />
<p class="para">
The <em>refcount</em> value returned by this function is
non-obvious in certain circumstances. For example, a developer might
expect the above example to indicate a <em>refcount</em> of
<em>2</em>. The third reference is created when actually
calling <span class="function"><strong>debug_zval_dump()</strong></span>.
</p>
<p class="para">
This behavior is further compounded when a variable is not passed to
<span class="function"><strong>debug_zval_dump()</strong></span> by reference. To illustrate, consider
a slightly modified version of the above example:
</p>
<p class="para">
<div class="example" id="example-5245">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$var1 </span><span style="color: #007700">= </span><span style="color: #DD0000">'Hello World'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$var2 </span><span style="color: #007700">= </span><span style="color: #DD0000">''</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">$var2 </span><span style="color: #007700">=& </span><span style="color: #0000BB">$var1</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">debug_zval_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$var1</span><span style="color: #007700">); </span><span style="color: #FF8000">// not passed by reference, this time<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>The above example will output:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
string(11) "Hello World" refcount(1)
</pre></div>
</div>
</div>
</p>
<p class="para">
Why <em>refcount(1)</em>? Because a copy of <em>$var1</em> is
being made, when the function is called.
</p>
<p class="para">
This function becomes even <em class="emphasis">more</em> confusing when a
variable with a <em>refcount</em> of <em>1</em> is
passed (by copy/value):
</p>
<p class="para">
<div class="example" id="example-5246">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$var1 </span><span style="color: #007700">= </span><span style="color: #DD0000">'Hello World'</span><span style="color: #007700">;<br /><br /></span><span style="color: #0000BB">debug_zval_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$var1</span><span style="color: #007700">);<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
<div class="example-contents"><p>The above example will output:</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
string(11) "Hello World" refcount(2)
</pre></div>
</div>
</div>
</p>
<p class="para">
A <em>refcount</em> of <em>2</em>, here, is extremely
non-obvious. Especially considering the above examples. So what's
happening?
</p>
<p class="para">
When a variable has a single reference (as did <em>$var1</em>
before it was used as an argument to <span class="function"><strong>debug_zval_dump()</strong></span>),
PHP's engine optimizes the manner in which it is passed to a function.
Internally, PHP treats <em>$var1</em> like a reference (in that
the <em>refcount</em> is increased for the scope of this
function), with the caveat that <em class="emphasis">if</em> the passed reference
happens to be written to, a copy is made, but only at the moment of
writing. This is known as "copy on write."
</p>
<p class="para">
So, if <span class="function"><strong>debug_zval_dump()</strong></span> happened to write to its sole
parameter (and it doesn't), then a copy would be made. Until then, the
parameter remains a reference, causing the <em>refcount</em> to
be incremented to <em>2</em> for the scope of the function call.
</p>
</p></blockquote>
</div>
<div class="refsect1 seealso" id="refsect1-function.debug-zval-dump-seealso">
<h3 class="title">See Also</h3>
<p class="para">
<ul class="simplelist">
<li class="member"> <span class="function"><a href="function.var-dump.html" class="function" rel="rdfs-seeAlso">var_dump()</a> - Dumps information about a variable</span></li>
<li class="member"> <span class="function"><a href="function.debug-backtrace.html" class="function" rel="rdfs-seeAlso">debug_backtrace()</a> - Generates a backtrace</span></li>
<li class="member"><a href="language.references.html" class="link">References Explained</a></li>
<li class="member"><a href="http://derickrethans.nl/php_references_article.php" class="link external">» References Explained (by Derick Rethans)</a></li>
</ul>
</p>
</div>
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