title: Why I can't see the extern function in the project?
body: <p>In my static lib project(target:sdk.a), I used an extern function like this:</p>
  
  <pre><code>// in the PlatformUnity.h file
  extern "C"{
      extern UIView * UnityGetGLView();  
      extern UIViewController * UnityGetGLViewController();
  
  }
  
  // in the PlatformUnity.mm file (*.mm NOT the *.m)
  
  UIView * funcA(){
      return UnityGetGLView();
  }
  
  UIViewController * funcB(){
      return UnityGetGLViewController();
  }
  </code></pre>
  
  <p>In another project named Unity-iPhone.xcodeproj, I used the SDK.a .
  And there's a file named AppController.mm contains the code below:</p>
  
  <pre><code>static UIViewController* sGLViewController = nil;
  UIViewController* UnityGetGLViewController()
  {
     return sGLViewController;
  }
  static UIView* sGLView = nil;
  UIView* UnityGetGLView()
  {
      return sGLView;
  }
  </code></pre>
  
  <p>When I build the Unity-iPhone.xcodeproj, It tells me that it can't find the function UnityGetGLView(). link error below:</p>
  
  <pre><code>Undefined symbols for architecture armv7:
    "_UnityGetGLViewController", referenced from:_funcB in SDK.a(PlatformUnity.o)
    "_UnityGetGLView", referenced from:_funcA in SDK.a(PlatformUnity.o)
  </code></pre>
  
  <p>This two function are really defined in AppController.mm But why I can't find it when link? The other linker flag of Unity-iPhone.xcodeproj is below:</p>
  
  <pre><code>-all_load -weak_framework CoreMotion -weak-lSystem
  </code></pre>