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Referencing variable from different code

Hello, I am modifying scalartransportFoam to make some multiple scalar properties I need. I first modified to create scalar named 'zeta', by modifying PDE from scalarTransport.c and changing name of scalar from 's' to 'zeta'. Then, i made another code which is also modified version of scalarTransport.c, which uses 'zeta' scalar for transport equation.

So, I tried to make the code gets data of 'zeta' as it does to rho and phi, so I wrote the line 'zetaName_ = dict.lookupOrDefault<word>("zeta", "zeta");' and 'mesh_.lookupObject<volScalarField>(zetaName_);' each below the part they reference rho and phi. However it seems like the code doesn't compile well.

Below is the error code

Code:

avgageTransport.C: In member function ‘virtual bool Foam::functionObjects::avgageTransport::read(const Foam::dictionary&)’:

avgageTransport.C:212:5: error: ‘zetaName_’ was not declared in this scope

  212 |     zetaName_ = dict.lookupOrDefault<word>("zeta", "zeta");

      |     ^~~~~~~~~

avgageTransport.C: In member function ‘virtual bool Foam::functionObjects::avgageTransport::execute()’:

avgageTransport.C:252:44: error: ‘zetaName_’ was not declared in this scope

  252 |         mesh_.lookupObject<volScalarField>(zetaName_);

      |                                            ^~~~~~~~~

avgageTransport.C:263:27: warning: unused variable ‘fvModels’ [-Wunused-variable]

  263 |     const Foam::fvModels& fvModels(Foam::fvModels::New(mesh_));

      |                           ^~~~~~~~

make: *** [/opt/openfoam11/wmake/rules/General/transform:26: Make/linux64GccDPInt32Opt/avgageTransport.o] Error 1

What may have caused the problem? Do these lookupOrDefault and lookupObject functions work different to rho/phi and zeta? I am not sure about how OF saves and load variable data

Quote:

error: ‘zetaName_’ was not declared in this scope

Looks like you forgot to declare the variable, zetaName_.

Do I have to externally declare the 'zetaName_'?

I thought the dict.lookupOrDefault is the function that creates the variable, since the function was doing the same job for rho and phi on original code, and they didn't have declared themselves before the 'rhoName_ = dict.lookupOrDefault<word>("rho", "rho");" stuffs... I am confused how the rhoName_ and phiName_ managed to compile without error but zetaName didn't.

Also, how does this function actually work? It seems like it searches for field named "zeta" from the dictionary, and uses the latter "zeta", i have no idea what actually means by the way.

Since zeta is also created from my another code which is modification of scalartransport, I'm not sure if it is actually stored in the so called 'dict', since I don't know how they do input on to the dictionary. Sorry for my low understanding in OF structure since I've just started OF programming...

Lots to unpack here!

Quote:

Do I have to externally declare the 'zetaName_'?

Yes - you have to declare it somewhere!

Quote:

I thought the dict.lookupOrDefault is the function that creates the variable, since the function was doing the same job for rho and phi on original code, and they didn't have declared themselves before the 'rhoName_ = dict.lookupOrDefault<word>("rho", "rho");" stuffs...

Nope. The lookupOrDefault function is just that - a function that returns an object. Look earlier in the coding and you'll see that both rho and phi are explicitly declared, eg

Code:

      const volScalarField& rho =

             mesh_.lookupObject<volScalarField>(rhoName_);

Quote:

I am confused how the rhoName_ and phiName_ managed to compile without error but zetaName didn't.

Check in scalarTransport.H and you'll find that they are defined as private members of the class.

Quote:

Also, how does this function actually work? It seems like it searches for field named "zeta" from the dictionary, and uses the latter "zeta", i have no idea what actually means by the way.

I assume you are talking about the lines like:

Code:

rhoName_ = dict.lookupOrDefault<word>("rho", "rho");

This line searches dictionary dict for keyword "rho" ... if it finds it, it reads the value and sets rhoName_ to it (i.e. uses that as the name for the rho field); if it doesn't find it, it uses the default name, which is the second "rho" in the brackets. i.e. it's just setting the name for the field. It's an optional dictionary entry, as you'll see from the .H file.

Quote:

Since zeta is also created from my another code which is modification of scalartransport, I'm not sure if it is actually stored in the so called 'dict', since I don't know how they do input on to the dictionary. Sorry for my low understanding in OF structure since I've just started OF programming...

Don't worry - you're on a long journey, but keep at it and gradually it will become easier. There is a LOT to take in, so my suggestions are:

1. brush up on your C++ programming skills
2. make extensive use of the Doxygen pages (eg https://cpp.openfoam.org/v8/scalarTr...8H_source.html)
3. Start to get your head around how OpenFOAM does things ... classes, dictionaries etc.
4. Google lots, to find helpful resources - there's plenty of training material, MSc theses etc. out there
5. try to work out the answers as much as you can, yourself - you'll learn enormously that way; come back to the forum when you get stuck

Good luck!

Oh god you are my livesaver! I had a bit experience on C, but never worked on such large software, so I've never thought of seeking variables in header file before.

Thank you very much. Now I got another clue about how OF works. Also, thanks for the last tip!