title: How to obtain (almost) unique system identifier in a cross platform way?
body: <p>I'm looking for a way to get a number which will almost surely change when running the code on different machines and almost surely stay the same between two runs on the same machine.</p>
  
  <p>If I were doing this as a shell script in Linux, I would use something like this:</p>
  
  <pre><code>{ uname -n ; cat /proc/meminfo | head -n1 ; cat /proc/cpuinfo ; } | md5sum
  </code></pre>
  
  <p>But I need this in C++ (with boost) and at least on Windows, Linux and Mac.</p>