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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>begin</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++ Maps</a> > <a href="begin.html">begin</a> </div> <div class="name-format"> begin </div> <div class="syntax-name-format"> Syntax: </div> <pre class="syntax-box"> #include <map> iterator begin(); const_iterator begin() const;</pre> <p>The function begin() returns an iterator to the first element of the map. begin() should run in <a href="../complexity.html">constant time</a>.</p> <p>For example, the following code uses begin() to initialize an iterator that is used to traverse a list:</p> <pre class="example-code"> map<string,int> stringCounts; string str; while( cin >> str ) stringCounts[str]++; map<string,int>::iterator iter; for( iter = stringCounts.begin(); iter != stringCounts.end(); iter++ ) { cout << "word: " << iter->first << ", count: " << iter->second << endl; }</pre> <p>When given this input:</p> <pre class="example-code"> here are some words and here are some more words</pre> <p>...the above code generates this output:</p> <pre class="example-code"> word: and, count: 1 word: are, count: 2 word: here, count: 2 word: more, count: 1 word: some, count: 2 word: words, count: 2</pre> <div class="related-name-format"> Related topics: </div> <div class="related-content"> <a href="end.html">end</a><br> <a href="rbegin.html">rbegin</a><br> <a href="rend.html">rend</a> </div> </div> </td> </tr> </table></body></html>⌨️ 快捷键说明
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