Hi Group, 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).
class ONetCDFFile : public NcFile {
public:
ONetCDFFile(const char * pathname, NcFile::FileMode fmode =
NcFile::ReadOnly,
size_t * chunksizeptr = NULL, size_t initialise = 0) :
NcFile(pathname, fmode, chunksizeptr, initialise) {
}
virtual ~ONetCDFFile(){ outputDims.clear(); }
virtual NcDim * add_dim(NcToken dimname, long dimsize){
if(outputDims.find(dimname) != outputDims.end()){
#ifdef DEBUG
cerr << __FILE__ << ":" << __LINE__ << " duplicated call to add_dim
" << dimname << ":" <<
dimsize << ":" << get_dim(dimname)->size() << endl;
#endif
return get_dim(dimname);
}
NcFile::add_dim(dimname, dimsize);
outputDims.insert(map<string, NcDim *>::value_type(dimname,
get_dim(dimname)) );
}
virtual NcDim * add_dim(NcToken dimname){
if(outputDims.find(dimname) != outputDims.end()){
#ifdef DEBUG
cerr << __FILE__ << ":" << __LINE__ << " duplicated call to add_dim
" << dimname << endl;
#endif
return get_dim(dimname);
}
NcFile::add_dim(dimname);
outputDims.insert(map<string, NcDim *>::value_type(dimname,
get_dim(dimname)) );
}
private:
map<string, NcDim *> outputDims;
};
--
Fei Liu, PhD. phone: 609-4526551
RSIS/GFDL/NOAA fax: 609-9875063
P.O. Box 308, 201 Forrestal Rd. http://www.gfdl.noaa.gov/~fil
Princeton, NJ 08542-0308 email: Fei.Liu@xxxxxxxx
