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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>at</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++ Double-ended Queues</a> > <a href= "at.html">at</a> </div> <div class="name-format"> at </div> <div class="syntax-name-format"> Syntax: </div> <pre class="syntax-box"> #include <deque> <a href="../containers.html">TYPE</a>& at( <strong>size_type</strong> loc ); const <a href="../containers.html">TYPE</a>& at( <strong>size_type</strong> loc ) const;</pre> <p>The at() function returns a reference to the element in the dequeue at index <em>loc</em>. The at() function is safer than the [] operator, because it won't let you reference items outside the bounds of the dequeue.</p> <p>For example, consider the following code:</p> <pre class="example-code"> vector<int> v( 5, 1 ); for( int i = 0; i < 10; i++ ) { cout << "Element " << i << " is " << v[i] << endl; } </pre> <p>This code overrunns the end of the vector, producing potentially dangerous results. The following code would be much safer:</p> <pre class="example-code"> vector<int> v( 5, 1 ); for( int i = 0; i < 10; i++ ) { cout << "Element " << i << " is " << v.at(i) << endl; } </pre> <p>Instead of attempting to read garbage values from memory, the at() function will realize that it is about to overrun the vector and will throw an exception.</p> <div class="related-name-format"> Related topics: </div> <div class="related-content"> (C++ Multimaps) <a href= "../cppmultimap/multimap_operators.html">Multimap operators</a><br> <a href="container_operators.html">Deque operators</a> </div> </div> </td> </tr> </table></body></html>⌨️ 快捷键说明
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