When I add variable in ardupilot, firmware can not be passed compilation

ArduPlane Plane 3.7
1 
Now I plan to use RC6 to switch on/off a servo. I try to add variable in https://github.com/ArduPilot/ardupilot/blob/master/ArduPlane/Parameters.h. I have created a file and add some subfunctionsin ArduPlane.

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However my firmware can not be passed compilation. Is there something wrong with it?
I'm looking forward your reply.Thanks  a lot.
2

Looking at your very first file (Parameters.h) it looks like you misspelled AP_ as Ap_. Identifiers in C/C++ are case sensitive. So:

AP_Int8 model_channel;