title: How to tell if program is running on x86/x64 or ARM Linux platforms
body: <p>In a <code>c</code> program I want to do different things. This program will run on x86/x64 based GNU/Linux system as well as ARM based one e.g. on a PC or RaspberryPI.</p>
  
  <p>Is there predefined macros in GCC to tell the platform?</p>
  
  <p>something like</p>
  
  <pre><code>#ifdef _X64_
     /do x64 stuff
  #elif _ARM_
  //do arm stuff
  #endif
  </code></pre>
  
  <p>Or maybe that is the wrong approach? I will be using <code>Makefile</code>to compile and I could get away with my own defines. </p>
  
  <p>What would be the best/safest approach?</p>