title: How to create #define that does nothing?
body: <p>I would like to use #define for locking/unlocking mutex. But on other platform where I only use single thread, I would like to disable locking and unlocking and do nothing.</p>
  
  <p>In this case, how can I safely define it on apps that I don't use the feature?</p>
  
  <p>For example, </p>
  
  <pre><code>#define SYS_LOCK sys_lock();
  #define SYS_UNLOCK sys_unlock();
  </code></pre>
  
  <p>This is what I use in platforms that support multithreads.</p>
  
  <p>But I want to disable it in on other platforms.</p>
  
  <p>Is it safe to define like this so calling SYS_LOCK and SYS_UNLOCK does nothing?</p>
  
  <pre><code>#define SYS_LOCK
  #define SYS_UNLOCK
  </code></pre>