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method surfaceSum(...) of class fvc

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Old   December 4, 2013, 08:42
Default method surfaceSum(...) of class fvc
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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?
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Old   December 4, 2013, 09:22
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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
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Old   December 4, 2013, 09:50
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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.

Last edited by maybee; December 4, 2013 at 13:04.
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Old   December 5, 2013, 04:35
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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
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Old   December 5, 2013, 05:12
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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".
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Old   December 5, 2013, 05:21
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Quote:
Originally Posted by maybee View Post
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.

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Old   December 5, 2013, 05:36
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, now I got it. Just one more question:

How did you know that ptr_ points to the geometricfield and not to the tmp<"geometricfield">?
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Old   December 5, 2013, 06:34
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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
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Old   December 5, 2013, 06:42
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Ok, thx alot. Question solved.
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