[user92]

Hello!

I appreciate any direct help with the topic below ... or a reference/guide/video which explains the full story for beginners
________________________________________________
my understanding of constructors in C++ is the following:

Class name (parameter list)
:
Member initializer list
{statement}

I tried to match with OpenFOAM using Lines 37 to 47 below from the code here

-------------------------------------------------
Foam:: prghPressureFvPatchScalarField::
prghPressureFvPatchScalarField
(
const fvPatch& p,
const DimensionedField<scalar, volMesh>& iF
)
:
fixedValueFvPatchScalarField(p, iF),
rhoName_("rho"),
p_(p.size(), Zero)
{}

-------------------------------------------------

My guess (please correct me if I'm wrong)
- Class name is prghPressureFvPatchScalarField

- fvPatch and DimensionedField<scalar, volMesh> are parameters and they were given aliases p and iF

my questions
- what is fixedValueFvPatchScalarField(p, iF)

- {} is empty, I'm not sure what the constructor is doing overall

- what is the first line Foam::X::X (I've seen this frequently in different codes)

Thank you

[geth03]

i commented the lines for you

Foam:: prghPressureFvPatchScalarField:: //Foam is the namespace :: yourClassName :: yourConstructorAsFunction
prghPressureFvPatchScalarField
(
const fvPatch& p,
const DimensionedField<scalar, volMesh>& iF
)
:
fixedValueFvPatchScalarField(p, iF), //your class inherits from this class, so
//this must be included, you cannot ignore
//the parent class, if multiple parents exist, do same for other parents
rhoName_("rho"), // next two lines overwrite attributes
p_(p.size(), Zero)
{} //you already overwrote attributes, so
// nothing to do for that class here,
// other classes might need it to do stuff

[user92]

Thank you I have a few more clarifications if you don't mind

Originally Posted by geth03

fixedValueFvPatchScalarField(p, iF), //your class inherits from this class,

I'm used to seeing braces {} used with classes, so I wonder what would className() mean? what are p & iF in this case? are they arguments? objects?

Originally Posted by geth03

rhoName_("rho"), // next two lines overwrite attributes
p_(p.size(), Zero)

to make sure I understood this, can I generalize it as variablename_(update)

where the update could be a new name or some changes on how the variable is defined

[geth03]

i don't quite get what you mean by className(),
but let my clarify few things.

p and iF are arguments for the function fixedValueFvPatchScalarField,
fixedValueFvPatchScalarField(p, iF) is a parameter constructor bc it takes arguments to construct an instance. what p and iF mean you can look up and decipher from the code (p means pressure, don't know what iF means, didnt look it up, maybe initialField?).

if you have a constructor without an argument (maybe you mean that by className()) you can create instances from that class without providing input.

next point:
if you want to update an attribute automatically when creating an instance of a class you can do this like
rhoName_("rho") // so rhoName_-value will be updated with rho-value.