Xcode build failure “Undefined symbols for architecture x86_64”
问题 An Xcode beginner's question: It is my first experience with Xcode 4.6.3. I am trying to write a very simple console program, that searches for paired BT devices and prints them to an NSLog. It builds with the following error: Undefined symbols for architecture x86_64: "_OBJC_CLASS_$_IOBluetoothDevice", referenced from: objc-class-ref 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) I searched like crazy.