<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en"
lang="en" dir="ltr">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>
sizeof [C++ Reference]
</title>
<meta name="generator" content="DokuWiki Release 2009-12-25c "Lemming"" />
<meta name="robots" content="index,follow" />
<meta name="date" content="2009-11-30T06:51:08-0800" />
<meta name="keywords" content="keywords,sizeof" />
<link rel="search" type="application/opensearchdescription+xml" href="/wiki/lib/exe/opensearch.php" title="C++ Reference" />
<link rel="start" href="/wiki/" />
<link rel="contents" href="/wiki/keywords/sizeof?do=index" title="Index" />
<link rel="alternate" type="application/rss+xml" title="Recent Changes" href="/wiki/feed.php" />
<link rel="alternate" type="application/rss+xml" title="Current Namespace" href="/wiki/feed.php?mode=list&ns=keywords" />
<link rel="edit" title="Edit this page" href="/wiki/keywords/sizeof?do=edit" />
<link rel="alternate" type="text/html" title="Plain HTML" href="/wiki/_export/xhtml/keywords/sizeof" />
<link rel="alternate" type="text/plain" title="Wiki Markup" href="/wiki/_export/raw/keywords/sizeof" />
<link rel="canonical" href="http://www.cppreference.com/wiki/keywords/sizeof" />
<link rel="stylesheet" media="all" type="text/css" href="/wiki/lib/exe/css.php?s=all&t=custom1&tseed=1272971091" />
<link rel="stylesheet" media="screen" type="text/css" href="/wiki/lib/exe/css.php?t=custom1&tseed=1272971091" />
<link rel="stylesheet" media="print" type="text/css" href="/wiki/lib/exe/css.php?s=print&t=custom1&tseed=1272971091" />
<script type="text/javascript" charset="utf-8" ><!--//--><![CDATA[//><!--
var NS='keywords';var JSINFO = {"id":"keywords:sizeof","namespace":"keywords"};
//--><!]]></script>
<script type="text/javascript" charset="utf-8" src="/wiki/lib/exe/js.php?tseed=1272971091" ></script>
<link rel="shortcut icon" href="/wiki/lib/tpl/custom1/images/favicon.png" />
</head>
<body>
<div class="dokuwiki">
<div class="stylehead">
<div class="breadcrumbs">
<span class="bchead">You are here: </span><a href="../start.html" title="start">C++ Reference</a> » <a href="../keywords/start.html" title="keywords:start">C++ Keywords</a> » <a href="../keywords/sizeof.html" title="keywords:sizeof">sizeof</a> </div>
</div>
<div class="page">
<script src="http://www.google-analytics.com/urchin.js" type="text/javascript">
</script>
<script type="text/javascript">
_uacct = "UA-2828341-1";
urchinTracker();
</script>
<!-- wikipage start -->
<h2><a name="sizeof" id="sizeof">sizeof</a></h2>
<div class="level2">
<p>
The <code>sizeof</code> operator is a compile-time operator that returns the size of the
argument passed to it.
</p>
<p>
The size is a multiple of the size of a <code>char</code>, which on
many personal computers is 1 byte (or 8 bits). The number of bits in a <code>char</code> is
stored in the <code>CHAR_BIT</code> constant defined in the <code><climits></code> header file.
</p>
<p>
For example, the following code uses <code>sizeof</code> to display the sizes of a number of
variables:
</p>
<pre class="c code c++" style="font-family:monospace;"> <span class="kw4">struct</span> EmployeeRecord <span class="br0">{</span>
<span class="kw4">int</span> ID<span class="sy0">;</span>
<span class="kw4">int</span> age<span class="sy0">;</span>
<span class="kw4">double</span> salary<span class="sy0">;</span>
EmployeeRecord<span class="sy0">*</span> boss<span class="sy0">;</span>
<span class="br0">}</span><span class="sy0">;</span>
...
<a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0"><<</span> <span class="st0">"sizeof(int): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span> <span class="sy0"><<</span> endl
<span class="sy0"><<</span> <span class="st0">"sizeof(float): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">float</span><span class="br0">)</span> <span class="sy0"><<</span> endl
<span class="sy0"><<</span> <span class="st0">"sizeof(double): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">double</span><span class="br0">)</span> <span class="sy0"><<</span> endl
<span class="sy0"><<</span> <span class="st0">"sizeof(char): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">char</span><span class="br0">)</span> <span class="sy0"><<</span> endl
<span class="sy0"><<</span> <span class="st0">"sizeof(EmployeeRecord): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span>EmployeeRecord<span class="br0">)</span> <span class="sy0"><<</span> endl<span class="sy0">;</span>
<span class="kw4">int</span> i<span class="sy0">;</span>
<span class="kw4">float</span> f<span class="sy0">;</span>
<span class="kw4">double</span> d<span class="sy0">;</span>
<span class="kw4">char</span> c<span class="sy0">;</span>
EmployeeRecord er<span class="sy0">;</span>
<a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0"><<</span> <span class="st0">"sizeof(i): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span>i<span class="br0">)</span> <span class="sy0"><<</span> endl
<span class="sy0"><<</span> <span class="st0">"sizeof(f): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span>f<span class="br0">)</span> <span class="sy0"><<</span> endl
<span class="sy0"><<</span> <span class="st0">"sizeof(d): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span>d<span class="br0">)</span> <span class="sy0"><<</span> endl
<span class="sy0"><<</span> <span class="st0">"sizeof(c): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span>c<span class="br0">)</span> <span class="sy0"><<</span> endl
<span class="sy0"><<</span> <span class="st0">"sizeof(er): "</span> <span class="sy0"><<</span> <span class="kw4">sizeof</span><span class="br0">(</span>er<span class="br0">)</span> <span class="sy0"><<</span> endl<span class="sy0">;</span></pre>
<p>
On some machines, the above code displays this output:
</p>
<pre class="c code c++" style="font-family:monospace;"> <span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy0">:</span> 4
<span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">float</span><span class="br0">)</span><span class="sy0">:</span> 4
<span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">double</span><span class="br0">)</span><span class="sy0">:</span> 8
<span class="kw4">sizeof</span><span class="br0">(</span><span class="kw4">char</span><span class="br0">)</span><span class="sy0">:</span> 1
<span class="kw4">sizeof</span><span class="br0">(</span>EmployeeRecord<span class="br0">)</span><span class="sy0">:</span> 20
<span class="kw4">sizeof</span><span class="br0">(</span>i<span class="br0">)</span><span class="sy0">:</span> 4
<span class="kw4">sizeof</span><span class="br0">(</span>f<span class="br0">)</span><span class="sy0">:</span> 4
<span class="kw4">sizeof</span><span class="br0">(</span>d<span class="br0">)</span><span class="sy0">:</span> 8
<span class="kw4">sizeof</span><span class="br0">(</span>c<span class="br0">)</span><span class="sy0">:</span> 1
<span class="kw4">sizeof</span><span class="br0">(</span>er<span class="br0">)</span><span class="sy0">:</span> <span class="nu0">20</span></pre>
<p>
Note that sizeof can either take a variable type (such as <code>int</code>) or a variable
name (such as <code>i</code> in the example above).
</p>
<p>
It is also important to note that the sizes of various types of variables can
change depending on what system you're on. Check out <a href="../data_types.html" class="wikilink1" title="data_types">the data types page</a> for more information.
</p>
<p>
The parentheses around the argument are only required if you are using sizeof
with a variable type (e.g. <code>sizeof(int)</code>). Parentheses can be left out if the argument is a variable or array (e.g. <code>sizeof x</code>, <code>sizeof myArray</code>).
</p>
<p>
Related Topics: <a href="../data_types.html" class="wikilink1" title="data_types">C++ Data Types</a>
</p>
</div>
<!-- wikipage stop -->
</div>
<div class="clearer"> </div>
<div class="stylefoot">
<div class="meta">
<div class="user">
</div>
<!--
<div class="doc">
keywords/sizeof.txt · Last modified: 11/30/2009 06:51 by nate </div>
-->
</div>
</div></div></body>
</html>