title: control conditional Openmp in #define macro
body: <p>I want to use a <code>#define</code> flag to control using openmp or not.  Since <code>#pragma</code> can't not be inside a <code>#define</code>, so I tried </p>
  
  <pre><code>#define USE_OPENMP  // Toggle this on/off
  
  #ifdef USE_OPENMP
      #define OMP_FOR(n)   __pragma("omp parallel for if(n&gt;10)") 
  #else
      #define OMP_FOR(n)   // do nothing        
  #endif
  </code></pre>
  
  <p>then in my code I can:</p>
  
  <pre><code>int size_of_the_loop = 11;
  OMP_FOR(size_of_the_loop) // activate openmp if(n&gt;10)
  for(){
      //do stuff
  }
  </code></pre>
  
  <p>I'm not familiar with the <code>#define</code> related stuff, and wondering if it's possible achieve this? Thanks.</p>