title: Double slash comment substituition within a macro
body: <p>I am developing a PIC MCU program on an ansi-compliant compiler (Microchip XC8).
  There are two operation modes, determined via macros during compilation time.
  So that I don't want to duplicate one function-like macro due to one line of code, I would like to know if there is any way to write a macro such as</p>
  
  <pre><code>#define FOO //
  </code></pre>
  
  <p>so that when FOO is substituted it will actually cancel the rest of the line.</p>
  
  <p>Writing a function instead of a macro is out of the question because the delay generated by function calls would disrupt the tight timings of my program (around some microseconds).</p>