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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>insert</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> > <a href= "index.html">C++ Vectors</a> > <a href="insert.html">insert</a> </div> <div class="name-format"> insert </div> <div class="syntax-name-format"> Syntax: </div> <pre class="syntax-box"> #include <vector> iterator insert( iterator loc, const <a href="../containers.html">TYPE</a>& val ); void insert( iterator loc, <strong>size_type</strong> num, const <a href="../containers.html">TYPE</a>& val ); template<<a href="../containers.html">TYPE</a>> void insert( iterator loc, <a href="../iterators.html">input_iterator</a> start, <a href="../iterators.html">input_iterator</a> end );</pre> <p>The insert() function either:</p> <ul> <li>inserts <em>val</em> before <em>loc</em>, returning an iterator to the element inserted,</li> <li>inserts <em>num</em> copies of <em>val</em> before <em>loc</em>, or</li> <li>inserts the elements from <em>start</em> to <em>end</em> before <em>loc</em>.</li> </ul> <p>Note that inserting elements into a vector can be relatively time-intensive, since the underlying data structure for a vector is an array. In order to insert data into an array, you might need to displace a lot of the elements of that array, and this can take <a href="../complexity.html">linear time</a>. If you are planning on doing a lot of insertions into your vector and you care about speed, you might be better off using a container that has a linked list as its underlying data structure (such as a <a href="../cpplist/index.html">List</a> or a <a href="../cppdeque/index.html">Deque</a>).</p> <p>For example, the following code uses the insert() function to splice four copies of the character 'C' into a vector of characters:</p> <pre class="example-code"> // Create a vector, load it with the first 10 characters of the alphabet vector<char> alphaVector; for( int i=0; i < 10; i++ ) { alphaVector.push_back( i + 65 ); } // Insert four C's into the vector vector<char>::iterator theIterator = alphaVector.begin(); alphaVector.insert( theIterator, 4, 'C' ); // Display the vector for( theIterator = alphaVector.begin(); theIterator != alphaVector.end(); theIterator++ ) { cout << *theIterator; } </pre> <p>This code would display:</p> <pre class="example-code"> CCCCABCDEFGHIJ </pre> <p>Here is another example of the insert() function. In this code, insert() is used to append the contents of one vector onto the end of another:</p> <pre class="example-code"> vector<int> v1; v1.push_back( 0 ); v1.push_back( 1 ); v1.push_back( 2 ); v1.push_back( 3 ); vector<int> v2; v2.push_back( 5 ); v2.push_back( 6 ); v2.push_back( 7 ); v2.push_back( 8 ); cout << "Before, v2 is: "; for( int i = 0; i < v2.size(); i++ ) { cout << v2[i] << " "; } cout << endl; v2.insert( v2.end(), v1.begin(), v1.end() ); cout << "After, v2 is: "; for( int i = 0; i < v2.size(); i++ ) { cout << v2[i] << " "; } cout << endl;</pre> <p>When run, this code displays:</p> <pre class="example-code"> Before, v2 is: 5 6 7 8 After, v2 is: 5 6 7 8 0 1 2 3</pre> <div class="related-name-format"> Related topics: </div> <div class="related-content"> <a href="assign.html">assign</a><br> <a href="erase.html">erase</a><br> <a href="push_back.html">push_back</a><br> (C++ Lists) <a href="../cpplist/merge.html">merge</a><br> (C++ Lists) <a href="../cpplist/push_front.html">push_front</a><br> (C++ Lists) <a href="../cpplist/splice.html">splice</a> </div> </div> </td> </tr> </table></body></html>⌨️ 快捷键说明
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