title: Can't assign variable to an extern'd variable in C
body: <p>Why does this not work</p>
  
  <pre><code>extern int externed_variable;
  int variable = externed_variable;
  </code></pre>
  
  <p>While this does</p>
  
  <pre><code>extern int externed_variable;
  int *variable_ptr = &amp;externed_variable;
  </code></pre>
  
  <p>The compiler error I get from the former is "expression must have a constant value". I am using MSVC.</p>