How can I write out a volscalarfield in openFOAM
 

I am trying to write out a volscalarfield 'a'. I define it in the library as follows

tmp<volScalarField> ta
(
new volScalarField
(
IOobject
(
"a",
mesh().time().timeName(),
mesh(),
IOobject::NO_READ,
IOobject::AUTO_WRITE
),
mesh(),
dimensionedScalar("a", dimless/dimLength, 0.0)
)
);

In the solve, in createFileds.H, i define it as

volScalarField a
(
IOobject
(
"a",
runTime.timeName(),
mesh,
IOobject::MUST_READ,
IOobject::AUTO_WRITE
),
mesh,
dimensionedScalar("a", dimensionSet(0,-1,0,0,0,0,0), 0.0)
);

But when I save field data for a given time step the it does create a file 'a' but there are no values and instead for each bounday patch it is written :

internalField uniform 0;

boundaryField
{
boundary1
{
type calculated;
value uniform 0;
}
}

can someone tell me how to write out any volscalarfield.

Why define two a's separately? Can you not define a separate variable for dimensionless a?

It looks like your a is not changing during simulation. Check that too

'a' is a dimensioned variable. I also have defined it as

AUTO-WRITE

in the code and removed it from createfields.H but it is still not writting for each time step.

1) If you don't want to read field from the file, then you must specify it's boundary types in constructor

2) volScalarField is a typedef for the GeomtricField<scalar, fvPatchScalarField, fvMesh>, full list of constructors you can find here

3) If you want to write your field at the each time step, you must call a.write()