Lesson/Example please

[Hal Murray]

[Context is cleaning up ntp_control]

This will probably be simple after somebody gives me a good example and/or 
explains things to me.

I want to put a (pointer to a) function in a field of a struct.
The type of that function includes a pointer to the struct.
I need to make several functions of that type.

I assume I want a typedef for the type of the function.

Can anybody give me a pointer to code that does this?  Or steer me in the 
right direction, or ...

There is a recursive tangle of struct needs function and function needs struct, but the function only needs a pointer to the struct so I think that should work.

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