[sina_mech]

Hi,

I'm trying to extract a double value of a velocity vector component (x-component), using the following code

scalar u = U[mycell].x();
scalar v = U[mycell].y();
scalar w = U[mycell].z();

double u1= u.value();

but I get an error:

error: âxâ was not declared in this scope

Do you have any suggestion?

[sina_mech]

Any comment?

[anishtain4]

please report the full error, I guess you can just use your u value, don't need to define another value as u1.

[sina_mech]

Originally Posted by anishtain4

please report the full error, I guess you can just use your u value, don't need to define another value as u1.

error: request for member âvalueâ in âuâ, which is of non-class type âFoam::scalar {aka double}â
   usina = u.value();

[hk318i]

This should work

double u1 = u;

scalar is basically OF wrap of standard c++ double/float

[sina_mech]

Originally Posted by hk318i

This should work

double u1 = u;

scalar is basically OF wrap of standard c++ double/float

Thank you. It works now

[Tobi]

By the way, why you do something like that?
As hk318i already stated, double and scalar are similar! This will only introduce a new operation of memory allocation etc. In addition I would use references instead of copy values!

scalar& u = u[cellI].x();
const scalar& u = u[cellI].x();

Or if you really want to have the explicit name "double"

double& u = u[cellI].x();
const double& u = u[cellI].x();

But why you should use "double" in OpenFOAM we use "scalar" and as we know a scalar is a double

using scalar = double;

[Jerryfan]

If you go to the source code of scalar, you will find that the scalar is the same thing as double. Besides, they add template specialization for pTraits<Scalar>.


In doubleScalar.H:

typedef double doubleScalar;

#define Scalar doubleScalar

And later in scalar.H:

typedef doubleScalar scalar;

Therefore, scalar would be equivalent to double in this regard.

In Scalar.H:

template<>
class pTraits<Scalar>
{....}