title: C++ append to existing file
body: <p>I'm trying to take data from multiple files and append them into one file using fstream, however whenever I try to output to an existing file using</p>
  
  <pre><code> std::ofstream Out("mushroom.csv", std::ofstream::app);
  </code></pre>
  
  <p>it outputs to the end of the file, I want it to append to the same line, for example if this is the previous file:</p>
  
  <pre><code> 1,2,3,4,5,6,7
   8,9,10,11,12,13
  </code></pre>
  
  <p>I want it to become:</p>
  
  <pre><code> 1,2,3,4,5,6,7,a,b,c
   8,9,10,11,12,13,c,d,e
  </code></pre>