title: Should functions be made "extern" in header files?
body: <p>Should functions be made <code>extern</code> in header files? Or are they <code>extern</code> by default?</p>
  
  <p>For example, should I write this:</p>
  
  <pre><code>// birthdays.h
  struct person find_birthday(const char* name);
  </code></pre>
  
  <p>or this:</p>
  
  <pre><code>// birthdays.h
  extern struct person find_birthday(const char* name);
  </code></pre>