title: cmake rm -rf build best practice
body: <p>I have seen that cmake does not have <code>cmake clean</code> 
  from <a href="https://stackoverflow.com/q/9680420/6329006">Looking for a &#39;cmake clean&#39; command to clear up cmake output</a>, When using cmake as to the following situation:</p>
  
  <ol>
  <li><p>source file change</p></li>
  <li><p>CMakeLists.txt change</p></li>
  <li><p>add new file or directory</p></li>
  <li><p>subdirectory(cmake) change</p></li>
  </ol>
  
  <p>and do on.</p>
  
  <p>We may need rebuild the project, lots of people will do <code>rm -rf *</code> in the build directory to clear the last build, and then <code>cmake ..</code> <code>make</code> to rebuild the project.This maybe very slow if the project is very big.And in some situation there is no need, just do make is enough.</p>
  
  <p>So my question is when should we do <code>rm -rf *</code> in the build directory and then rebuild the project and when not ? Is there any best practice?</p>