title: VC++ Visual Studio added .hpp files in subdirectory but get "Error: cannot open source file ..."
body: <p>This is driving me nuts - I've added a number of .hpp files in subdirectories in the root of an existing VC++ projects source directory.</p>
  
  <p>Visual Studio complains "Error: cannot open source file ..." but if I right click on the  and select open document, VS can display it.</p>
  
  <p>I've tried:</p>
  
  <ul>
  <li>"Rescan solution" which appears to do nothing.</li>
  <li>Adding existing item (both on it's own and with a "filter" - which appears to be a directory?)</li>
  <li>Closing the project and VStudio in the vain hope it would eventually discover the directories/files I'd added</li>
  </ul>
  
  <p>VStudio complains it cannot find these files when it is capable of opening them?  My question is simply this:  "How can I add a directory containing source files to a VC++ project such that the linker/complier can see them?</p>
  
  <p>(disclaimer; i've never used Visual Studio before or many Microsoft products, so am finding this all very alien)</p>