title: Extern functions in C vs C++
body: <p>In <code>*.h</code> header files of a <code>C</code> library, should one declare functions</p>
  
  <pre><code>extern void f();
  
  // or only 
  
  void f();
  </code></pre>
  
  <ol>
  <li>when using only in <code>C</code></li>
  <li>when using from <code>C++</code>.</li>
  </ol>