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<title>Comparison Operators</title>
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</div><hr /><div id="language.operators.comparison" class="sect1">
<h2 class="title">Comparison Operators</h2>
<p class="simpara">
Comparison operators, as their name implies, allow you to compare
two values. You may also be interested in viewing
<a href="types.comparisons.html" class="link">the type comparison tables</a>,
as they show examples of various type related comparisons.
</p>
<table class="doctable table">
<caption><strong>Comparison Operators</strong></caption>
<thead>
<tr>
<th>Example</th>
<th>Name</th>
<th>Result</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td>$a == $b</td>
<td>Equal</td>
<td><strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is equal to <var class="varname"><var class="varname">$b</var></var> after type juggling.</td>
</tr>
<tr>
<td>$a === $b</td>
<td>Identical</td>
<td>
<strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is equal to <var class="varname"><var class="varname">$b</var></var>, and they are of the same
type.
</td>
</tr>
<tr>
<td>$a != $b</td>
<td>Not equal</td>
<td><strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is not equal to <var class="varname"><var class="varname">$b</var></var> after type juggling.</td>
</tr>
<tr>
<td>$a <> $b</td>
<td>Not equal</td>
<td><strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is not equal to <var class="varname"><var class="varname">$b</var></var> after type juggling.</td>
</tr>
<tr>
<td>$a !== $b</td>
<td>Not identical</td>
<td>
<strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is not equal to <var class="varname"><var class="varname">$b</var></var>, or they are not of the same
type.
</td>
</tr>
<tr>
<td>$a < $b</td>
<td>Less than</td>
<td><strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is strictly less than <var class="varname"><var class="varname">$b</var></var>.</td>
</tr>
<tr>
<td>$a > $b</td>
<td>Greater than</td>
<td><strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is strictly greater than <var class="varname"><var class="varname">$b</var></var>.</td>
</tr>
<tr>
<td>$a <= $b</td>
<td>Less than or equal to </td>
<td><strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is less than or equal to <var class="varname"><var class="varname">$b</var></var>.</td>
</tr>
<tr>
<td>$a >= $b</td>
<td>Greater than or equal to </td>
<td><strong><code>TRUE</code></strong> if <var class="varname"><var class="varname">$a</var></var> is greater than or equal to <var class="varname"><var class="varname">$b</var></var>.</td>
</tr>
</tbody>
</table>
<p class="para">
If you compare a number with a string or the comparison involves numerical
strings, then each string is
<a href="language.types.string.html#language.types.string.conversion" class="link">converted to a number</a>
and the comparison performed numerically. These rules also apply to the
<a href="control-structures.switch.html" class="link">switch</a> statement. The
type conversion does not take place when the comparison is === or !== as
this involves comparing the type as well as the value.
<div class="informalexample">
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">0 </span><span style="color: #007700">== </span><span style="color: #DD0000">"a"</span><span style="color: #007700">); </span><span style="color: #FF8000">// 0 == 0 -> true<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #DD0000">"1" </span><span style="color: #007700">== </span><span style="color: #DD0000">"01"</span><span style="color: #007700">); </span><span style="color: #FF8000">// 1 == 1 -> true<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #DD0000">"10" </span><span style="color: #007700">== </span><span style="color: #DD0000">"1e1"</span><span style="color: #007700">); </span><span style="color: #FF8000">// 10 == 10 -> true<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">100 </span><span style="color: #007700">== </span><span style="color: #DD0000">"1e2"</span><span style="color: #007700">); </span><span style="color: #FF8000">// 100 == 100 -> true<br /><br /></span><span style="color: #007700">switch (</span><span style="color: #DD0000">"a"</span><span style="color: #007700">) {<br />case </span><span style="color: #0000BB">0</span><span style="color: #007700">:<br /> echo </span><span style="color: #DD0000">"0"</span><span style="color: #007700">;<br /> break;<br />case </span><span style="color: #DD0000">"a"</span><span style="color: #007700">: </span><span style="color: #FF8000">// never reached because "a" is already matched with 0<br /> </span><span style="color: #007700">echo </span><span style="color: #DD0000">"a"</span><span style="color: #007700">;<br /> break;<br />}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
For various types, comparison is done according to the following
table (in order).
</p>
<table id="language.operators.comparison.types" class="doctable table">
<caption><strong>Comparison with Various Types</strong></caption>
<thead>
<tr>
<th>Type of Operand 1</th>
<th>Type of Operand 2</th>
<th>Result</th>
</tr>
</thead>
<tbody class="tbody">
<tr>
<td><span class="type"><a href="language.types.null.html" class="type null">null</a></span> or <span class="type"><a href="language.types.string.html" class="type string">string</a></span></td>
<td><span class="type"><a href="language.types.string.html" class="type string">string</a></span></td>
<td>Convert <strong><code>NULL</code></strong> to "", numerical or lexical comparison</td>
</tr>
<tr>
<td><span class="type"><a href="language.types.boolean.html" class="type bool">bool</a></span> or <span class="type"><a href="language.types.null.html" class="type null">null</a></span></td>
<td>anything</td>
<td>Convert both sides to <span class="type"><a href="language.types.boolean.html" class="type bool">bool</a></span>, <strong><code>FALSE</code></strong> < <strong><code>TRUE</code></strong></td>
</tr>
<tr>
<td><span class="type"><a href="language.types.object.html" class="type object">object</a></span></td>
<td><span class="type"><a href="language.types.object.html" class="type object">object</a></span></td>
<td>Built-in classes can define its own comparison, different classes
are uncomparable, same class - compare properties the same way as
arrays (PHP 4), PHP 5 has its own <a href="language.oop5.object-comparison.html" class="link">explanation</a>
</td>
</tr>
<tr>
<td><span class="type"><a href="language.types.string.html" class="type string">string</a></span>, <span class="type"><a href="language.types.resource.html" class="type resource">resource</a></span> or <span class="type"><a href="language.pseudo-types.html#language.types.number" class="type number">number</a></span></td>
<td><span class="type"><a href="language.types.string.html" class="type string">string</a></span>, <span class="type"><a href="language.types.resource.html" class="type resource">resource</a></span> or <span class="type"><a href="language.pseudo-types.html#language.types.number" class="type number">number</a></span></td>
<td>Translate strings and resources to numbers, usual math</td>
</tr>
<tr>
<td><span class="type"><a href="language.types.array.html" class="type array">array</a></span></td>
<td><span class="type"><a href="language.types.array.html" class="type array">array</a></span></td>
<td>Array with fewer members is smaller, if key from operand 1 is not
found in operand 2 then arrays are uncomparable, otherwise - compare
value by value (see following example)</td>
</tr>
<tr>
<td><span class="type"><a href="language.types.object.html" class="type object">object</a></span></td>
<td>anything</td>
<td><span class="type"><a href="language.types.object.html" class="type object">object</a></span> is always greater</td>
</tr>
<tr>
<td><span class="type"><a href="language.types.array.html" class="type array">array</a></span></td>
<td>anything</td>
<td><span class="type"><a href="language.types.array.html" class="type array">array</a></span> is always greater</td>
</tr>
</tbody>
</table>
<p class="para">
<div class="example" id="example-121">
<p><strong>Example #1 Boolean/null comparison</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// Bool and null are compared as bool always<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">1 </span><span style="color: #007700">== </span><span style="color: #0000BB">TRUE</span><span style="color: #007700">); </span><span style="color: #FF8000">// TRUE - same as (bool)1 == TRUE<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">0 </span><span style="color: #007700">== </span><span style="color: #0000BB">FALSE</span><span style="color: #007700">); </span><span style="color: #FF8000">// TRUE - same as (bool)0 == FALSE<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">100 </span><span style="color: #007700">< </span><span style="color: #0000BB">TRUE</span><span style="color: #007700">); </span><span style="color: #FF8000">// FALSE - same as (bool)100 < TRUE<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(-</span><span style="color: #0000BB">10 </span><span style="color: #007700">< </span><span style="color: #0000BB">FALSE</span><span style="color: #007700">);</span><span style="color: #FF8000">// FALSE - same as (bool)-10 < FALSE<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">min</span><span style="color: #007700">(-</span><span style="color: #0000BB">100</span><span style="color: #007700">, -</span><span style="color: #0000BB">10</span><span style="color: #007700">, </span><span style="color: #0000BB">NULL</span><span style="color: #007700">, </span><span style="color: #0000BB">10</span><span style="color: #007700">, </span><span style="color: #0000BB">100</span><span style="color: #007700">)); </span><span style="color: #FF8000">// NULL - (bool)NULL < (bool)-100 is FALSE < TRUE<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
<div class="example" id="example-122">
<p><strong>Example #2 Transcription of standard array comparison</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// Arrays are compared like this with standard comparison operators<br /></span><span style="color: #007700">function </span><span style="color: #0000BB">standard_array_compare</span><span style="color: #007700">(</span><span style="color: #0000BB">$op1</span><span style="color: #007700">, </span><span style="color: #0000BB">$op2</span><span style="color: #007700">)<br />{<br /> if (</span><span style="color: #0000BB">count</span><span style="color: #007700">(</span><span style="color: #0000BB">$op1</span><span style="color: #007700">) < </span><span style="color: #0000BB">count</span><span style="color: #007700">(</span><span style="color: #0000BB">$op2</span><span style="color: #007700">)) {<br /> return -</span><span style="color: #0000BB">1</span><span style="color: #007700">; </span><span style="color: #FF8000">// $op1 < $op2<br /> </span><span style="color: #007700">} elseif (</span><span style="color: #0000BB">count</span><span style="color: #007700">(</span><span style="color: #0000BB">$op1</span><span style="color: #007700">) > </span><span style="color: #0000BB">count</span><span style="color: #007700">(</span><span style="color: #0000BB">$op2</span><span style="color: #007700">)) {<br /> return </span><span style="color: #0000BB">1</span><span style="color: #007700">; </span><span style="color: #FF8000">// $op1 > $op2<br /> </span><span style="color: #007700">}<br /> foreach (</span><span style="color: #0000BB">$op1 </span><span style="color: #007700">as </span><span style="color: #0000BB">$key </span><span style="color: #007700">=> </span><span style="color: #0000BB">$val</span><span style="color: #007700">) {<br /> if (!</span><span style="color: #0000BB">array_key_exists</span><span style="color: #007700">(</span><span style="color: #0000BB">$key</span><span style="color: #007700">, </span><span style="color: #0000BB">$op2</span><span style="color: #007700">)) {<br /> return </span><span style="color: #0000BB">null</span><span style="color: #007700">; </span><span style="color: #FF8000">// uncomparable<br /> </span><span style="color: #007700">} elseif (</span><span style="color: #0000BB">$val </span><span style="color: #007700">< </span><span style="color: #0000BB">$op2</span><span style="color: #007700">[</span><span style="color: #0000BB">$key</span><span style="color: #007700">]) {<br /> return -</span><span style="color: #0000BB">1</span><span style="color: #007700">;<br /> } elseif (</span><span style="color: #0000BB">$val </span><span style="color: #007700">> </span><span style="color: #0000BB">$op2</span><span style="color: #007700">[</span><span style="color: #0000BB">$key</span><span style="color: #007700">]) {<br /> return </span><span style="color: #0000BB">1</span><span style="color: #007700">;<br /> }<br /> }<br /> return </span><span style="color: #0000BB">0</span><span style="color: #007700">; </span><span style="color: #FF8000">// $op1 == $op2<br /></span><span style="color: #007700">}<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<p class="para">
See also <span class="function"><a href="function.strcasecmp.html" class="function">strcasecmp()</a></span>,
<span class="function"><a href="function.strcmp.html" class="function">strcmp()</a></span>,
<a href="language.operators.array.html" class="link">Array operators</a>,
and the manual section on
<a href="language.types.html" class="link">Types</a>.
</p>
<div class="warning"><strong class="warning">Warning</strong>
<h1 class="title">Comparison of floating point numbers</h1>
<p class="para">
Because of the way <span class="type"><a href="language.types.float.html" class="type float">float</a></span>s are represented internally, you
should not test two <span class="type"><a href="language.types.float.html" class="type float">float</a></span>s for equality.
</p>
<p class="para">
See the documentation for <span class="type"><a href="language.types.float.html" class="type float">float</a></span> for more information.
</p>
</div>
<div class="sect2" id="language.operators.comparison.ternary">
<h3 class="title">Ternary Operator</h3>
<p class="para">
Another conditional operator is the "?:" (or ternary) operator.
<div class="example" id="example-123">
<p><strong>Example #3 Assigning a default value</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// Example usage for: Ternary Operator<br /></span><span style="color: #0000BB">$action </span><span style="color: #007700">= (empty(</span><span style="color: #0000BB">$_POST</span><span style="color: #007700">[</span><span style="color: #DD0000">'action'</span><span style="color: #007700">])) ? </span><span style="color: #DD0000">'default' </span><span style="color: #007700">: </span><span style="color: #0000BB">$_POST</span><span style="color: #007700">[</span><span style="color: #DD0000">'action'</span><span style="color: #007700">];<br /><br /></span><span style="color: #FF8000">// The above is identical to this if/else statement<br /></span><span style="color: #007700">if (empty(</span><span style="color: #0000BB">$_POST</span><span style="color: #007700">[</span><span style="color: #DD0000">'action'</span><span style="color: #007700">])) {<br /> </span><span style="color: #0000BB">$action </span><span style="color: #007700">= </span><span style="color: #DD0000">'default'</span><span style="color: #007700">;<br />} else {<br /> </span><span style="color: #0000BB">$action </span><span style="color: #007700">= </span><span style="color: #0000BB">$_POST</span><span style="color: #007700">[</span><span style="color: #DD0000">'action'</span><span style="color: #007700">];<br />}<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
The expression <em>(expr1) ? (expr2) : (expr3)</em>
evaluates to <span class="replaceable">expr2</span> if
<span class="replaceable">expr1</span> evaluates to <strong><code>TRUE</code></strong>, and
<span class="replaceable">expr3</span> if
<span class="replaceable">expr1</span> evaluates to <strong><code>FALSE</code></strong>.
</p>
<p class="para">
Since PHP 5.3, it is possible to leave out the middle part of the ternary
operator. Expression <em>expr1 ?: expr3</em> returns
<span class="replaceable">expr1</span> if <span class="replaceable">expr1</span>
evaluates to <strong><code>TRUE</code></strong>, and <span class="replaceable">expr3</span> otherwise.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<span class="simpara">
Please note that the ternary operator is a statement, and that it
doesn't evaluate to a variable, but to the result of a statement. This
is important to know if you want to return a variable by reference.
The statement <em>return $var == 42 ? $a : $b;</em> in a
return-by-reference function will therefore not work and a warning is
issued in later PHP versions.
</span>
</p></blockquote>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
It is recommended that you avoid "stacking" ternary expressions. PHP's
behaviour when using more than one ternary operator within a single
statement is non-obvious:
<div class="example" id="example-124">
<p><strong>Example #4 Non-obvious Ternary Behaviour</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">// on first glance, the following appears to output 'true'<br /></span><span style="color: #007700">echo (</span><span style="color: #0000BB">true</span><span style="color: #007700">?</span><span style="color: #DD0000">'true'</span><span style="color: #007700">:</span><span style="color: #0000BB">false</span><span style="color: #007700">?</span><span style="color: #DD0000">'t'</span><span style="color: #007700">:</span><span style="color: #DD0000">'f'</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// however, the actual output of the above is 't'<br />// this is because ternary expressions are evaluated from left to right<br /><br />// the following is a more obvious version of the same code as above<br /></span><span style="color: #007700">echo ((</span><span style="color: #0000BB">true </span><span style="color: #007700">? </span><span style="color: #DD0000">'true' </span><span style="color: #007700">: </span><span style="color: #0000BB">false</span><span style="color: #007700">) ? </span><span style="color: #DD0000">'t' </span><span style="color: #007700">: </span><span style="color: #DD0000">'f'</span><span style="color: #007700">);<br /><br /></span><span style="color: #FF8000">// here, you can see that the first expression is evaluated to 'true', which<br />// in turn evaluates to (bool)true, thus returning the true branch of the<br />// second ternary expression.<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
</p></blockquote>
</div>
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