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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head>  <meta name="generator" content=  "HTML Tidy for Linux/x86 (vers 1 September 2005), see www.w3.org">  <title>Container constructors</title>  <link href="../cppreference.css" rel="stylesheet" type="text/css"></head><body><table>  <tr>  <td>  <div class="body-content">  <div class="header-box">    <a href="../index.html">cppreference.com</a> &gt; <a href=    "index.html">C++ Lists</a> &gt; <a href=    "container_constructors2.html">Container constructors</a>  </div>  <div class="name-format">    Container constructors  </div>  <div class="syntax-name-format">    Syntax:  </div>  <pre class="syntax-box">  #include &lt;list&gt;  container();  container( const container&amp; c );  container( <strong>size_type</strong> num, const <a href="../containers.html">TYPE</a>&amp; val = <a href="../containers.html">TYPE</a>() );  container( <a href="../iterators.html">input_iterator</a> start, <a href="../iterators.html">input_iterator</a> end );  ~container();</pre>  <p>The default list constructor takes no arguments, creates a new  instance of that list.</p>  <p>The second constructor is a default copy constructor that can be  used to create a new list that is a copy of the given list  <em>c</em>.</p>  <p>The third constructor creates a list with space for <em>num</em>  objects. If <em>val</em> is specified, each of those objects will be  given that value. For example, the following code creates a vector  consisting of five copies of the integer 42:</p>  <pre class="example-code"> vector&lt;int&gt; v1( 5, 42 );         </pre>  <p>The last constructor creates a list that is initialized to contain  the elements between <em>start</em> and <em>end</em>. For  example:</p>  <pre class="example-code"> // create a vector of random integers cout &lt;&lt; &quot;original vector: &quot;; vector&lt;int&gt; v; for( int i = 0; i &lt; 10; i++ ) {   int num = (int) rand() % 10;   cout &lt;&lt; num &lt;&lt; &quot; &quot;;   v.push_back( num ); } cout &lt;&lt; endl;             // find the first element of v that is even vector&lt;int&gt;::iterator iter1 = v.begin(); while( iter1 != v.end() &amp;&amp; *iter1 % 2 != 0 ) {   iter1++; }               // find the last element of v that is even vector&lt;int&gt;::iterator iter2 = v.end(); do {   iter2--; } while( iter2 != v.begin() &amp;&amp; *iter2 % 2 != 0 );               cout &lt;&lt; &quot;first even number: &quot; &lt;&lt; *iter1 &lt;&lt; &quot;, last even number: &quot; &lt;&lt; *iter2 &lt;&lt; endl;          cout &lt;&lt; &quot;new vector: &quot;; vector&lt;int&gt; v2( iter1, iter2 ); for( int i = 0; i &lt; v2.size(); i++ ) {   cout &lt;&lt; v2[i] &lt;&lt; &quot; &quot;; } cout &lt;&lt; endl;            </pre>  <p>When run, this code displays the following output:</p>  <pre class="example-code"> original vector: 1 9 7 9 2 7 2 1 9 8 first even number: 2, last even number: 8 new vector: 2 7 2 1 9          </pre>  <p>All of these constructors run in <a href=  "../complexity.html">linear time</a> except the first, which runs in  <a href="../complexity.html">constant time</a>.</p>  <p>The default destructor is called when the list should be  destroyed.</p>  </div>  </td>    </tr>  </table></body></html>
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