title: Qt link library (C++ mix with objective C) error
body: <ol>
  <li>I am using Qt to build UI Application, </li>
  <li>The Qt application supposed to link to a static library (.a file)</li>
  <li>The library is written by C++ and Objective C (*.mm) files.</li>
  <li>I setup the Qt project file and linked the static library, but Qt Creator always gets linking error, and error is related with the function implement on *.mm which locates in the static library.
  <hr></li>
  </ol>
  
  <p>Question:<br>
  The Qt application how to link the library? 
  that's pure C++ application (Qt application) link to static library with C++ and ObjectiveC mixed (.a file).</p>
  
  <hr>
  
  <p>update: link error</p>
  
  <pre><code>Undefined symbols for architecture x86_64:
    "_OBJC_CLASS_$_QTCaptureDevice", referenced from:
    objc-class-ref in libmyapi.a(myTestFunction_mac.o)
    "_QTMediaTypeVideo", referenced from:
        myTestFunction() in myapi.a(myTestFunction_mac.o)
  ld: symbol(s) not found for architecture x86_64
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  make: *** [myApp.app/Contents/MacOS/myApp] Error 1
  14:38:06: The process "/usr/bin/make" exited with code 2.
  Error while building/deploying project myApp (kit: Desktop Qt 5.1.0 clang 64bit)
  </code></pre>
  
  <ol>
  <li>Qt5.1 with clang, support C++11</li>
  <li>static library myapi.a, built by Xcode4.6 without error. Only one file is myTestFunction_mac, using QTKit framework.</li>
  <li>myApp links myapi.a, but the myTestFunction_mac.mm implantation file has linking error. </li>
  </ol>