[mart.hein]

Hello everybody!

I try to read two files only if a certain condition is met. Unfortunatelly I don't know how to separately declare and initialize a volScalarField and a dimensionedScalar. My first approach did not work, because after the end of the if-conditions both variables "C" and "DC" are lost:

if (condition)
{
                volScalarField C
                (
                        IOobject
                        (
                                "C",
                                runTime.timeName(),
                                mesh,
                                IOobject::MUST_READ,
                                IOobject::AUTO_WRITE
                        ),
                        mesh
                );

                // read the transportProperties file
                IOdictionary transportProperties
                (
                        IOobject
                        (
                                "transportProperties",
                                runTime.constant(),
                                mesh,
                                IOobject::MUST_READ,
                                IOobject::NO_WRITE
                        )
                );

                // diffusion coefficient for the passive scalar
                dimensionedScalar& DC
                (
                        transportProperties.lookup("DC")
                );
}

How can I declare "C" and "DC" outside the if-condition and initialize them inside?

Thanks a lot for your help!

Regards

Martin

[cliffoi]

This is a C++ issue. Strictly speaking you can't optionally declare a variable. What you can do, however, is declare a pointer (or autoPtr) to the volScalarField, initialize it as NULL, and optionally set the pointer in the if-condition. Using autoPtr is the safest option since the object will automatically destruct at the end of your program.
For the dimensionedScalar I'd just declare it anyway since it uses up so little memory and use a bool to check it it has been set afterwards.

autoPtr<volScalarField> C;

dimensionedScalar DC("DC", dimless, 0);   

if (condition)
{
    C.set(new volScalarField
    (
        IOobject
        (
            "C",
            runTime.timeName(),
            mesh,
            IOobject::MUST_READ,
            IOobject::AUTO_WRITE
        ),
        mesh
    ));

    DC = dimensionedScalar(transportProperties.lookup("DC"));
}

[mart.hein]

Thank you cliffoi for your help! It works now