title: Difference between file.is_open() and file.fail()
body: <p>Initialization of <code>file</code>:</p>
  
  <pre><code>ifstream file("filename.txt");
  </code></pre>
  
  <p>What's is the difference between <code>if ( file.is_open() )</code> and <code>if (! file.fail() )</code> ?</p>
  
  <p>What Should I use to make sure if the file is ready for I/O ?</p>
  
  <p>We assume that variable <code>file</code> contains a object of a file stream. </p>