[WUYing]

Hi, I am new to OpenFOAM coding and have a few questions when studying the sample code.

1. The source file XXX.C generally includes a few parts, such as Static Member Functions, Protected Member Functions, Constructors, Destructor and Member Functions.
Q1. What is the difference between Protected Member Functions and Member Functions?
Q2. If I understand correctly, the Constructors is equivalent to the main function, determining how the solver is been used. (Please correct me if I make mistake)

2. I notice that some functions are virtual, so in what cases can a function be defined as a virtual function?

3. In the sample code, there are one fixed entry "A" (must be run) and two optional entries "B" and "C" (run if the entries are included in fvOptions file). Now I modify the sample code to change "A" as an optional entry like "B" and "C" and I don't define "A" in the fvOptions file. So "A" would not be executed during running, but I always receive the error :
keyword A is undefined in dictionary ".....fvOptions".

The output error only show the absent definition of A in fvOptions, is there any way to find the location of the error in the source code?

Any suggestion is welcome! Thanks!