title: Implicit declaration of function objc_getAssociatedObject is invalid in C99
body: <p>I'm trying to use Associated Objects on my objective-c category and I'm getting this warning.</p>
  
  <pre><code>Implicit declaration of function 'objc_getAssociatedObject' is invalid in C99
  </code></pre>
  
  <p>Also I'm using arc if that makes a difference.</p>