title: how to use object-Cpp in Xcode
body: <p>I created a new cocoa application in Xcode with 3 *.m files (main.m, AppDelegate.m, and projectnameTests.m). 
  In order to to use object-cpp, I renamed the 3 *.m files to *.mm files. </p>
  
  <p>Then I get this following error from Xcode: </p>
  
  <blockquote>
    <p>"Undefined symbols for architecture x86_64:
      "_NSApplicationMain", referenced from:
          _main in main.o
    ld: symbol(s) not found for architecture x86_64
    clang: error: linker command failed with exit code 1 (use -v to see invocation)"</p>
  </blockquote>
  
  <p>I have never dealt .o files, so am not sure what's wrong.
  Please help.</p>
  
  <p>P.S.: I use the latest Xcode, version(6.1.1).</p>