Data Export for 3D Cube?

I am trying to print the result at a specified point in a 3D cubic domain by the script:

cout<< "value of T at (0,0,0) = "<< T(0,0,0)<<endl;

but an error message is showing as:

but it is throwing error as:

Also, I am not able to export the results due to this error

Kindly help me to fix this issue!!!

This issue has been solved by @zhaog6 Sir. by implementing vectorial form of other variables:

Vh [u, v, w, unused] = [dy(S3) - dz(S2), dz(S1) - dx(S3), dx(S2) - dy(S1), 0];

Thanks, @zhaog6 Sir for your kind support.