title: ifstream: how to tell if specified file doesn't exist
body: <p>I want to open a file for reading. However, in the context of this program, it's OK if the file doesn't exist, I just move on. I want to be able to identify when the error is "file not found" and when the error is otherwise. Otherwise means I need to quit and error.</p>
  
  <p>I don't see an obvious way to do this with <code>fstream</code>.</p>
  
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  <p>I can do this with C's <code>open()</code> and <code>perror()</code>. I presumed that there was a <code>fstream</code> way to do this as well.</p>