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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>C++ I/O Examples</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++ I/O</a> &gt; <a href="examples.html">Examples</a>  </div>  <div class="name-format">    C++ I/O Examples  </div>  <h2>Reading From Files</h2>  <p>Assume that we have a file named <em>data.txt</em> that  contains this text:</p>  <pre class="example-data">  Fry: One Jillion dollars.  [Everyone gasps.]  Auctioneer: Sir, that's not a number.  [Everyone gasps.] </pre>  <p>We could use this code to read data from the file, word by word:</p>  <pre class="example-code">  ifstream fin("data.txt");  string s;  while( fin &gt;&gt; s ) {    cout &lt;&lt; "Read from file: " &lt;&lt; s &lt;&lt; endl;  }</pre>  <p>When used in this manner, we'll get space-delimited bits of text  from the file:</p>  <pre class="example-output">  Read from file: Fry:  Read from file: One  Read from file: Jillion  Read from file: dollars.  Read from file: [Everyone  Read from file: gasps.]  Read from file: Auctioneer:  Read from file: Sir,  Read from file: that's  Read from file: not  Read from file: a  Read from file: number.  Read from file: [Everyone  Read from file: gasps.]</pre>  <p>Note that in the previous example, all of the whitespace that  separated words (including newlines) was lost.  If we were  interested in preserving whitespace, we could read the file in  line-by-line using the <a href="getline.html">I/O getline() function</a>.</p>  <pre class="example-code">  ifstream fin("data.txt");  const int LINE_LENGTH = 100;  char str[LINE_LENGTH];  while( fin.getline(str,LINE_LENGTH) ) {    cout &lt;&lt; "Read from file: " &lt;&lt; str &lt;&lt; endl;  }</pre>  <p>Reading line-by-line produces the following output:</p>  <pre class="example-output">  Read from file: Fry: One Jillion dollars.  Read from file: [Everyone gasps.]  Read from file: Auctioneer: Sir, that's not a number.  Read from file: [Everyone gasps.]</pre>  <p>If you want to avoid reading into character arrays, you can use  the <a href="../cppstring/getline.html">C++ string getline()</a> function  to read lines into <a href="../cppstring/index.html">strings</a>:</p>  <pre class="example-code">  ifstream fin("data.txt");  string s;  while( getline(fin,s) ) {    cout &lt;&lt; "Read from file: " &lt;&lt; s &lt;&lt; endl;  }</pre>  <h2>Checking For Errors</h2>  <p>Simply evaluating an I/O object in a boolean context will return  false if any errors have occurred:</p>  <pre class="example-code">  string filename = "data.txt";  ifstream fin( filename.c_str() );  if( !fin ) {    cout &lt;&lt; "Error opening " &lt;&lt; filename &lt;&lt; " for input" &lt;&lt; endl;    exit(-1);  }</pre>  </div>  </td>    </tr>  </table></body></html>
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