title: Cmake find header files matching cpp code
body: <p>I know there are a thousand questions like this but I'm struggling even after looking at those. </p>
  
  <p>My directory tree</p>
  
  <pre><code>./src/main/cpp/main.cpp
  ./src/main/cpp/CascadeLoader.cpp
  ./resources/headers/CascadeLoader.h
  </code></pre>
  
  <p>If in main.cpp I use </p>
  
  <pre><code>#include "CascadeLoader.cpp"
  </code></pre>
  
  <p>my code works but if I do a </p>
  
  <pre><code>#include "CascadeLoader.h"
  </code></pre>
  
  <p>I get a build error of </p>
  
  <pre><code>undefined reference to CascadeLoader::CascadeLoader()
  </code></pre>
  
  <p>my CMakeLists.txt I added</p>
  
  <pre><code>cmake_minimum_required(VERSION 2.8)
  project( ASLInterpreter )
  find_package ( OpenCV REQUIRED )
  include_directories( ${OpenCV_INCLUDE_DIRS} )
  add_executable( ASLInterpreter src/main/cpp/main.cpp )
  target_link_libraries( ASLInterpreter ${OpenCV_LIBS} )
  </code></pre>