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-   -   What is the role of tmp%2360T class objects (http://www.cfd-online.com/Forums/openfoam-solving/58548-what-role-tmp-2360t-class-objects.html)

nicasch September 17, 2008 04:29

Dear OF users, I have a lit
 
Dear OF users,

I have a little doubt on using tmp<t> objects and could use some help. I understand that a tmp<t> object is used to somehow automatically allocate and deallocate a temporary object. Many function members in OF classes use a tmp<t> objects as a return type, for example:

class someClass
{
// Private data
private:
dimensionedScalar s_;
volScalarField F_;

public:
// Constructor
// Destructor
// etc...

// Member functions
tmp<volscalarfield> sF() const
{
return s_*F_;
}
};

After calling the function sF() in some calculation in main() e.g. fvc::interpolate(someClass.sF()), a volScalarField is created within the function sF() as a product s_*F_. But, why should the return type from the function not be simply a const volScalarField& instead of tmp<volscalarfield>? The tmp<t> object stores a pointer to a temporary object in addition to its reference. But, since the product s_*F_ is already a temporary volScalarField it should go out of scope after leaving the function sF(). Does this means that the pointer to s_*F_ is reset to NULL immediately after return from function?

What exactly is being returned from this kind of functions and what are generally the benefits of using tmp<t> objects?

Thanks for any advice/explanation and best regards to all.


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