I found that for CFO compensation, there is the module named "costas_loop_cc ()" Use it in this way: gr.costas_loop_cc(alpha, beta, max_freq, min_freq, order)
where I can find this C++ file? I search the files, only found one "gr_costas_loop_cc.cc" in ~/gnuradio-3.2.2/gnuradio-core/src/lib/general
But It seems like this C++ function is not the one they use. As I tried to print out some variable, but no observations.