Here is the link.

From the first page

"However, an important factor in the logging facility's design is the ability to effectively "no-op" the logging statements at compile time."

Note that a stream based compile time on/off method works easily

// in header
#ifdef NDEBUG
  #define MY_DEBUG if( 0 ) cerr
#else
  #define MY_DEBUG if( should_runtime_show() ) \
    get_real_stream_reference(); \
  else \
    get_null_stream_reference();
#endif

 // in program
  MY_DEBUG << "foo" << endl;