title: Visual Studio warning about copies of files with different contents
body: <p>When I go to debug my C++ project in Visual Studio, up pops a little warning dialogue box that tells me:</p>
  
  <pre><code>A copy of datum.h was found in
  c:/users/brad/desktop/source/binary/datum.h, but the current
  source code is different from the version built into
  c:/users/brad/desktop/source/binary/datum.h.
  </code></pre>
  
  <p>I'm having trouble understanding what this is even trying to tell me, let alone how to fix it. At first I thought it might be complaining that I'd accidentally duplicated a file in the directory, which I checked, and found nothing of the sort, which leaves me pretty stumped. I also tried excluding the file from the solution and adding it again, which didn't fix the problem either.</p>
  
  <p>The warning doesn't appear to actually hinder the development of my project, but I suppose warnings exist for a reason, so if anyone knows what's gone wrong, any advice would be greatly appreciated. To my knowledge, I didn't change anything to cause the message to appear, it just popped up one time I went to debug the solution and has kept on appearing ever since.</p>
  
  <p>Also, more copies of the same warning have started popping up, pertaining to other header files in my solution (I haven't recieved any about .cpp files yet, but it could be a coincidence, because it's only been going on for about 20 minutes).</p>