title: What are "cerr" and "stderr"?
body: <p>What is the difference between them and how are they used?
  Can anyone point me to examples?</p>
  
  <p>Specifically, how do you "write" to the stream in both cases and how do you recover and output (i.e. to the screen) the text that had been written to it?</p>
  
  <p>Also, the "screen" output is itself a stream right? Maybe I don't understand streams well enough. This can also be saved to a file of course, I know. Would all of these use <code>fprintf</code> / <code>fscanf</code>, etc?</p>