CFD Online Discussion Forums - method surfaceSum(...) of class fvc

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- - method surfaceSum(...) of class fvc (https://www.cfd-online.com/Forums/openfoam-programming-development/127138-method-surfacesum-class-fvc.html)

method surfaceSum(...) of class fvc

hi,

I' m having problems with understanding the method surfaceSum(...) below:

Code:

template<class Type>

  192 tmp<GeometricField<Type, fvPatchField, volMesh> > surfaceSum

  193 (

  194     const tmp<GeometricField<Type, fvsPatchField, surfaceMesh> >& tssf

  195 )

  196 {

  197     tmp<GeometricField<Type, fvPatchField, volMesh> > tvf = surfaceSum(tssf());  //QUESTION

  198     tssf.clear();  

  199     return tvf;

  200 }

with the overloaded operator () called on tssf in line 197:

Code:

 

template<class T>

213*inline const T& Foam::tmp<T>::operator()() const       

214*{

215* if (isTmp_)   // bool isTmp_;  //- Flag for whether object is a temporary or a constant object

216* {

217* if (!ptr_)   //mutable T* ptr_;  //- Pointer to temporary object  

218* {

219* FatalErrorIn("const T& Foam::tmp<T>::operator()() const")

220* << "temporary deallocated"

221* << abort(FatalError);

222* }

223*

224* return *ptr_; 

225* }

226* else

227* {

228* return ref_;   //const T& ref_  //- Const reference to constant object

229* }

230*}

Question (line 197 marked in code snippet 1) :

In method surfaceSum(...) the input parameter tssf is passed to "another" surfaceSum(...) method. Wouldn t that cause some kind of endless loop, because in the new called method surfaceSum(...) the method gets called again and so on?

The ()-operator strips the object from it's tmp-"shell", so the following call to surfaceSum leads to a different method, namely one that is called when a GeometricField is passed: http://foam.sourceforge.net/docs/cpp...ce.html#l00138

hi again,

Quote:

The ()-operator strips the object from it's tmp-"shell",...

What do you mean by this? How is tmp stripped from the object tssf?

All I can see in the method operator () is that in line 215 it is proved if the object is tmp (temporary) and in line 217 if the pointer ptr_ is not NULL. If both these conditions are fullfilled the pointer ptr_ is dereferenced and returned in line 224.

Code:

224* return *ptr_;

* What does this line do?

It dereferences the pointer stored in the tmp<> object, and returns the dereferenced pointer.

* What happens if you dereference a pointer pointing to an object?

You get access to that object. Note that in our case, the object in question is a vol*Field.

Does that make things clear?

Recommended reading: http://openfoamwiki.net/index.php/OpenFOAM_guide/tmp

Quote:

224* return *ptr_;

What does this line do?

It dereferences the pointer stored in the tmp<> object, and returns the dereferenced pointer.

* What happens if you dereference a pointer pointing to an object?

You get access to that object. Note that in our case, the object in question is a vol*Field.

1. I know about dereferencing a pointer :), but if the pointer ptr_ points to an object of class tmp and gets dereferenced how should this strip the tmp from the object?

2. Furthermore, how do you know it is a vol*Field?

I have the following source code:

Code:

scalarField sumPhi

(

fvc::surfaceSum(mag(phi))().internalField()

);

with

Code:

const surfaceScalarField& phi

and therefore

Code:

→ template<class Type, template<class> class PatchField, class GeoMesh>

323*tmp<GeometricField<scalar, PatchField, GeoMesh> > mag  

324*(                                                                                                   

325* const GeometricField<Type, PatchField, GeoMesh>& gf    

326*)

327*{

328* tmp<GeometricField<scalar, PatchField, GeoMesh> > tMag    

329* (

330* new GeometricField<scalar, PatchField, GeoMesh>     

331* (                                                                                       

332* IOobject

333* (

334* "mag(" + gf.name() + ')', 

335* gf.instance(),                                      

336* gf.db(),                                    

337* IOobject::NO_READ,

338* IOobject::NO_WRITE

339* ),

340* gf.mesh(),                     

341* gf.dimensions()                                             

342* )

343* );

344*

345* mag(tMag(), gf);

346*

347* return tMag;

348*}

and since the overloaded operator () [see my first post] is called on the result of method mag which returns a "tmp<GeometricField<scalar, PatchField, GeoMesh> > tMag" the pointer ptr_ should point at a "tmp<scalar> field".

Quote:

Originally Posted by maybee (Post 464943)

1. I know about dereferencing a pointer :), but if the pointer ptr_ points to an object of class tmp and gets dereferenced how should this strip the tmp from the object?

I figured you would after getting this far, but the next guy with the same question may not :)

tmp<GeometricField<scalar, PatchField, GeoMesh> > tMag stores a pointer to a GeometricField<scalar, PatchField, GeoMesh>, which is the same thing as a volScalarField. So when you call tMag() you will end up with the underlying volScalarField.

- Anton

:D , now I got it. Just one more question:

How did you know that ptr_ points to the geometricfield and not to the tmp<"geometricfield">?

On line 330 of the code you posted a new object of GeometricField<> is allocated and it's pointer is passed on to the constructor of tmp<>: http://foam.sourceforge.net/docs/cpp...bf3c32f4c76004

Ok, thx alot. Question solved.