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Re: NcFile and its non-virtual member functions

Hi Fei Liu,

> ... this is a C++ related question about netCDF class design. I am
> wondering if it's possible to change NcFile implementation in the future
> to declare some of its member functions virtual, especially add_dim and
> add_var because they are not flexible enough. For example, I included a
> ONetCDFFile class implementation inherited from NcFile where I override
> add_dim function.  But since add_dim is non-virtual in base class NcFile,
> I have to either stick to ONetCDFFile everywhere a variable is referred to
> or use dynamic_cast to downcast type. It's not possible to use polymorphic
> features that C++ provided. e.g.
> 
> ONetCDFFile of(...);
> do_file(&of);
> 
> void do_file(NcFile * of){
>   of->add_dim(..); // Wrong, we really intended to use ONetCDFFile::add_dim
>   ..
> }
> 
> I understand the memory overhead associated with virtual functions but I 
> think it's a non-issue in scientific computing where large dataset is the 
> norm. I think it'd be a better design to declare some member functions 
> virtual in netcdfcpp, specifically, NcFile::add_dim, NcFile::add_var, 
> NcFile::~NcFile (as a general rule, always declare destructor virtual when 
> virtual member function is present).

These are good suggestions, and we will incorporate them into the C++
interface for a future release.  Unfortunately, it's too late to get
your changes in the 3.6.1 release, which has been out for a week but
won't be announced until next Monday.

Thanks again for your efforts to improve netCDF.  If you have other
suggestions for improving the C++ interface, feel free to send them to
address@hidden.

--Russ

_____________________________________________________________________

Russ Rew                                         UCAR Unidata Program
address@hidden                     http://www.unidata.ucar.edu