title: Trouble adding Obj-C++ subproject into a Xcode Obj-C project
body: <p>I created a Objective-C++ project that runs some C++ (OpenCV) code. It runs fine and everything works well. But then I decided to add these routines as a subproject to my MAIN PROJECT, I get errors whenever I try to use the subproject classes.</p>
  
  <p>The thing is, my SUBPROJECT uses <strong>.mm</strong> source files whereas my MAIN PROJECT uses only <strong>.m</strong> source files: <img src="https://i.stack.imgur.com/cVWxJ.png" alt="enter image description here"></p>
  
  <p>Every time I try to allocate a the class DyOpenCV (<code>DyOpenCv *opencv = [DyOpenCv alloc]</code>), I get a lot of errors: <img src="https://i.stack.imgur.com/I5zi3.png" alt="Compilation errors"></p>
  
  <p>Is that a tip to merge Obj-C with Obj-Cpp projects? 
  Is that a special interface to use, once I am trying to run <strong>.mm</strong> files from <strong>.m</strong> ones? Even if the <strong>.mm</strong> files are from a subproject?
  Is it necessary to add all libraries of my subproject to my project (I already did that)?</p>
  
  <p>Cheers,</p>