title: difference of pid_t and int in C
body: <p>what's the difference between pid_t datatype and int when getting process id?
  I saw something like:</p>
  
  <pre><code>pid_t getpid(void);
  </code></pre>
  
  <p>but whats the difference between it and </p>
  
  <pre><code>int getpid(void);
  </code></pre>