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<p>Provides the default initial value to a new object.
</p>
<table id="toc" class="toc"><tr><td>
<div id="toctitle"><h2>Contents</h2></div>
<ul>
<li class="toclevel-1 tocsection-1"><a href="#Syntax"><span class="tocnumber">1</span> <span class="toctext">Syntax</span></a></li>
<li class="toclevel-1 tocsection-2"><a href="#Explanation"><span class="tocnumber">2</span> <span class="toctext">Explanation</span></a></li>
<li class="toclevel-1 tocsection-3"><a href="#Notes"><span class="tocnumber">3</span> <span class="toctext">Notes</span></a></li>
<li class="toclevel-1 tocsection-4"><a href="#Example"><span class="tocnumber">4</span> <span class="toctext">Example</span></a></li>
<li class="toclevel-1 tocsection-5"><a href="#See_also"><span class="tocnumber">5</span> <span class="toctext">See also</span></a></li>
</ul>
</td></tr></table>
<h3>
<span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php" title="Edit section: Syntax">edit</a>]</span> <span class="mw-headline" id="Syntax">Syntax</span>
</h3>
<table class="t-sdsc-begin">

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<td colspan="10" class="t-sdsc-sep">
</td>
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<tr class="t-sdsc">
<td> <span class="t-spar">T</span> <span class="t-spar">object</span> <code><b>;</b></code>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td>
</tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td>
</tr>
<tr class="t-sdsc">
<td> <code><b>new </b></code> <span class="t-spar">T</span> <code><b>;</b></code>
</td>
<td> (2)
</td>
<td class="t-sdsc-nopad">
</td>
</tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
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<h3>
<span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php" title="Edit section: Explanation">edit</a>]</span> <span class="mw-headline" id="Explanation">Explanation</span>
</h3>
<p>Default initialization is performed in three situations:
</p>
<div class="t-li1">
<span class="t-li">1)</span> when a variable with automatic storage duration is declared with no initializer</div>
<div class="t-li1">
<span class="t-li">2)</span> when an object with dynamic storage duration is created by a new-expression without an initializer</div>
<div class="t-li1">
<span class="t-li">3)</span> when a base class or a non-static data member is not mentioned in a constructor <a href="initializer_list.html" title="cpp/language/initializer list">initializer list</a> and that constructor is called.</div>
<p>The effects of default initialization are:
</p>
<ul><li> If <code>T</code> is a class type, the <a href="default_constructor.html" title="cpp/language/default constructor">default constructor</a> is called to provide the initial value for the new object.
</li></ul>
<ul><li> If <code>T</code> is an array type, every element of the array is default-initialized.
</li></ul>
<ul><li> Otherwise, nothing is done.
</li></ul>
<p>If <code>T</code> is a const-qualified type, it must be a class type with a user-provided default constructor.
</p>
<h3>
<span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php" title="Edit section: Notes">edit</a>]</span> <span class="mw-headline" id="Notes">Notes</span>
</h3>
<p>Default initialization of non-class variables with automatic and dynamic storage duration produces objects with indeterminate values (static and thread-local objects get <a href="zero_initialization.html" title="cpp/language/zero initialization">zero initialized</a>)
</p>
<p>Reference cannot be default-initialized.
</p>
<h3>
<span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php" title="Edit section: Example">edit</a>]</span> <span class="mw-headline" id="Example">Example</span>
</h3>
<div class="t-example">
<div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">Run this code</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;string&gt;</span>
<span class="kw1">struct</span> T1 <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">class</span> T2 <span class="br0">{</span> 
    <span class="kw4">int</span> mem<span class="sy4">;</span>
 <span class="kw1">public</span><span class="sy4">:</span>
    T2<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span> <span class="co1">// "mem" not in initializer list</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> n<span class="sy4">;</span> <span class="co1">// This is not default-initialization, the value is zero.</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">int</span> n<span class="sy4">;</span>            <span class="co1">// non-class: the value is undeterminate</span>
    <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a> s<span class="sy4">;</span>    <span class="co1">// calls default ctor, the value is "" (empty string)</span>
    <a href="../string/basic_string.html"><span class="kw1045">std::<span class="me2">string</span></span></a> a<span class="br0">[</span><span class="nu0">2</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// calls default ctor, creates two empty strings</span>
<span class="co1">//    int&amp; r;         // error: default-initializing a reference</span>
<span class="co1">//    const int n;    // error: const non-class type</span>
<span class="co1">//    const T1 nd;    // error: const class type with implicit ctor</span>
    T1 t1<span class="sy4">;</span> <span class="co1">// ok, calls implicit default ctor</span>
    <span class="kw4">const</span> T2 t2<span class="sy4">;</span> <span class="co1">// ok, calls the user-provided default ctor </span>
                 <span class="co1">// t2.mem is default-initialized (to indeterminate value)</span>
<span class="br0">}</span></pre></div></div>
<p><br> 
</p>
</div>
<h3>
<span class="editsection">[<a href="http://en.cppreference.com/mwiki/index.php" title="Edit section: See also">edit</a>]</span> <span class="mw-headline" id="See_also">See also</span>
</h3>
<ul>
<li> <a href="direct_initialization.html" title="cpp/language/direct initialization">direct initialization</a>
</li>
<li> <a href="copy_initialization" title="cpp/language/copy initialization">copy initialization</a>
</li>
<li> <a href="list_initialization.html" title="cpp/language/list initialization">list initialization</a>
</li>
</ul>

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