title: How to append to a C++ preprocessor macro?
body: <p>A macro like <code>M_PI</code> is pretty useful, but it defines its value as a <code>double</code>. When using it as a float, you can't write <code>M_PIf</code>, because that obviously changes the name of the macro.</p>
  
  <p><em>How can I append text to a macro?</em></p>