Source of: /manual/en/language.types.integer.php
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<div id="language.types.integer" class="sect1">
<h2 class="title">Integers</h2>
<p class="simpara">
An <a href="language.types.integer.php" class="type integer">integer</a> is a number of the set
Z = {..., -2, -1, 0, 1, 2, ...}.
</p>
<p class="para">
See also:
</p>
<ul class="itemizedlist">
<li class="listitem">
<span class="simpara">
<a href="ref.gmp.php" class="link">Arbitrary length integer / GMP</a>
</span>
</li>
<li class="listitem">
<span class="simpara">
<a href="language.types.float.php" class="link">Floating point numbers</a>
</span>
</li>
<li class="listitem">
<span class="simpara">
<a href="ref.bc.php" class="link">Arbitrary precision / BCMath</a>
</span>
</li>
</ul>
<div id="language.types.integer.syntax" class="sect2">
<h3 class="title">Syntax</h3>
<p class="simpara">
<a href="language.types.integer.php" class="type Integer">Integer</a>s can be specified in decimal (base 10), hexadecimal
(base 16), or octal (base 8) notation, optionally preceded by a sign
(- or +).
</p>
<p class="para">
To use octal notation, precede the number with a <i>0</i> (zero).
To use hexadecimal notation precede the number with <i>0x</i>.
</p>
<div class="example">
<p><b>Example #1 Integer literals</b></p>
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$a </span><span style="color: #007700">= </span><span style="color: #0000BB">1234</span><span style="color: #007700">; </span><span style="color: #FF8000">// decimal number<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= -</span><span style="color: #0000BB">123</span><span style="color: #007700">; </span><span style="color: #FF8000">// a negative number<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">0123</span><span style="color: #007700">; </span><span style="color: #FF8000">// octal number (equivalent to 83 decimal)<br /></span><span style="color: #0000BB">$a </span><span style="color: #007700">= </span><span style="color: #0000BB">0x1A</span><span style="color: #007700">; </span><span style="color: #FF8000">// hexadecimal number (equivalent to 26 decimal)<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<p class="para">
Formally, the structure for <a href="language.types.integer.php" class="type integer">integer</a> literals is:
</p>
<div class="informalexample">
<div class="example-contents programlisting">
<div class="cdata"><pre>
decimal : [1-9][0-9]*
| 0
hexadecimal : 0[xX][0-9a-fA-F]+
octal : 0[0-7]+
integer : [+-]?decimal
| [+-]?hexadecimal
| [+-]?octal
</pre></div>
</div>
</div>
<p class="para">
The size of an <a href="language.types.integer.php" class="type integer">integer</a> is platform-dependent, although a maximum
value of about two billion is the usual value (that's 32 bits signed).
64-bits platforms usually have the maximum value of about 9E18. PHP
does not support unsigned <a href="language.types.integer.php" class="type integer">integer</a>s. <a href="language.types.integer.php" class="type Integer">Integer</a> size
can be determined using the constant <b><tt class="constant">PHP_INT_SIZE</tt></b>, and
maximum value using the constant <b><tt class="constant">PHP_INT_MAX</tt></b> since
PHP 4.4.0 and PHP 5.0.5.
</p>
<div class="warning"><b class="warning">Warning</b>
<p class="para">
If an invalid digit is given in an octal <a href="language.types.integer.php" class="type integer">integer</a> (i.e. 8 or 9),
the rest of the number is ignored.
</p>
<div class="example">
<p><b>Example #2 Octal weirdness</b></p>
<div class="example-contents programlisting">
<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">01090</span><span style="color: #007700">); </span><span style="color: #FF8000">// 010 octal = 8 decimal<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</div>
</div>
<div id="language.types.integer.overflow" class="sect2">
<h3 class="title">Integer overflow</h3>
<p class="para">
If PHP encounters a number beyond the bounds of the <a href="language.types.integer.php" class="type integer">integer</a>
type, it will be interpreted as a <a href="language.types.float.php" class="type float">float</a> instead. Also, an
operation which results in a number beyond the bounds of the
<a href="language.types.integer.php" class="type integer">integer</a> type will return a <a href="language.types.float.php" class="type float">float</a> instead.
</p>
<div class="informalexample">
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br />$large_number </span><span style="color: #007700">= </span><span style="color: #0000BB">2147483647</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$large_number</span><span style="color: #007700">);<br /></span><span style="color: #FF8000">// output: int(2147483647)<br /><br /></span><span style="color: #0000BB">$large_number </span><span style="color: #007700">= </span><span style="color: #0000BB">2147483648</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$large_number</span><span style="color: #007700">);<br /></span><span style="color: #FF8000">// output: float(2147483648)<br /><br />// it's true also for hexadecimal specified integers between 2^31 and 2^32-1:<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">( </span><span style="color: #0000BB">0xffffffff </span><span style="color: #007700">);<br /></span><span style="color: #FF8000">// output: float(4294967295)<br /><br />// this doesn't go for hexadecimal specified integers above 2^32-1:<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">( </span><span style="color: #0000BB">0x100000000 </span><span style="color: #007700">);<br /></span><span style="color: #FF8000">// output: int(2147483647)<br /><br /></span><span style="color: #0000BB">$million </span><span style="color: #007700">= </span><span style="color: #0000BB">1000000</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$large_number </span><span style="color: #007700">= </span><span style="color: #0000BB">50000 </span><span style="color: #007700">* </span><span style="color: #0000BB">$million</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">$large_number</span><span style="color: #007700">);<br /></span><span style="color: #FF8000">// output: float(50000000000)<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<div class="warning"><b class="warning">Warning</b>
<p class="simpara">
Unfortunately, there was a bug in PHP which caused this to not always work
correctly when negative numbers were involved. For example, the result of
<i>-50000 * $million</i> is <i>-429496728</i>.
However, when both operands were positive, there was no problem.
</p>
<p class="simpara">
This was fixed in PHP 4.1.0.
</p>
</div>
<p class="para">
There is no <a href="language.types.integer.php" class="type integer">integer</a> division operator in PHP.
<i>1/2</i> yields the <a href="language.types.float.php" class="type float">float</a> <i>0.5</i>.
The value can be casted to an <a href="language.types.integer.php" class="type integer">integer</a> to round it downwards, or
the <a href="function.round.php" class="function">round()</a> function provides finer control over rounding.
</p>
<div class="informalexample">
<div class="example-contents programlisting">
<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">25</span><span style="color: #007700">/</span><span style="color: #0000BB">7</span><span style="color: #007700">); </span><span style="color: #FF8000">// float(3.5714285714286) <br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">((int) (</span><span style="color: #0000BB">25</span><span style="color: #007700">/</span><span style="color: #0000BB">7</span><span style="color: #007700">)); </span><span style="color: #FF8000">// int(3)<br /></span><span style="color: #0000BB">var_dump</span><span style="color: #007700">(</span><span style="color: #0000BB">round</span><span style="color: #007700">(</span><span style="color: #0000BB">25</span><span style="color: #007700">/</span><span style="color: #0000BB">7</span><span style="color: #007700">)); </span><span style="color: #FF8000">// float(4) <br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</div>
<div id="language.types.integer.casting" class="sect2">
<h3 class="title">Converting to integer</h3>
<p class="simpara">
To explicitly convert a value to <a href="language.types.integer.php" class="type integer">integer</a>, use either the
<i>(int)</i> or <i>(integer)</i> casts. However, in
most cases the cast is not needed, since a value will be automatically
converted if an operator, function or control structure requires an
<a href="language.types.integer.php" class="type integer">integer</a> argument. A value can also be converted to
<a href="language.types.integer.php" class="type integer">integer</a> with the <a href="function.intval.php" class="function">intval()</a> function.
</p>
<p class="simpara">
See also: <a href="language.types.type-juggling.php" class="link">type-juggling</a>.
</p>
<div id="language.types.integer.casting.from-boolean" class="sect3">
<h4 class="title">From <a href="language.types.boolean.php" class="link">booleans</a></h4>
<p class="simpara">
<b><tt class="constant">FALSE</tt></b> will yield <i>0</i> (zero), and <b><tt class="constant">TRUE</tt></b> will yield
<i>1</i> (one).
</p>
</div>
<div id="language.types.integer.casting.from-float" class="sect3">
<h4 class="title">
From <a href="language.types.float.php" class="link">floating point numbers</a>
</h4>
<p class="simpara">
When converting from <a href="language.types.float.php" class="type float">float</a> to <a href="language.types.integer.php" class="type integer">integer</a>, the number
will be rounded <em class="emphasis">towards zero</em>.
</p>
<p class="para">
If the float is beyond the boundaries of <a href="language.types.integer.php" class="type integer">integer</a> (usually
<i>+/- 2.15e+9 = 2^31</i>), the result is undefined, since the
<a href="language.types.float.php" class="type float">float</a> doesn't have enough precision to give an exact
<a href="language.types.integer.php" class="type integer">integer</a> result. No warning, not even a notice will be issued
when this happens!
</p>
<div class="warning"><b class="warning">Warning</b>
<p class="para">
Never cast an unknown fraction to <a href="language.types.integer.php" class="type integer">integer</a>, as this can
sometimes lead to unexpected results.
</p>
<div class="informalexample">
<div class="example-contents programlisting">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #007700">echo (int) ( (</span><span style="color: #0000BB">0.1</span><span style="color: #007700">+</span><span style="color: #0000BB">0.7</span><span style="color: #007700">) * </span><span style="color: #0000BB">10 </span><span style="color: #007700">); </span><span style="color: #FF8000">// echoes 7!<br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<p class="para">
See also the <a href="language.types.float.php#warn.float-precision" class="link">warning about float
precision</a>.
</p>
</div>
</div>
<div id="language.types.integer.casting.from-string" class="sect3">
<h4 class="title">From strings</h4>
<p class="simpara">
See <a href="language.types.string.php#language.types.string.conversion" class="link">String conversion to
numbers</a>
</p>
</div>
<div id="language.types.integer.casting.from-other" class="sect3">
<h4 class="title">From other types</h4>
<div class="caution"><b class="caution">Caution</b>
<p class="simpara">
The behaviour of converting to <a href="language.types.integer.php" class="type integer">integer</a> is undefined for other
types. Do <em class="emphasis">not</em> rely on any observed behaviour, as it
can change without notice.
</p>
</div>
</div>
</div>
</div><?php manual_footer(); ?>
