Section: 12.3 Using the Classic Model

12.3 Using the Classic Model

NetCDF-4 files can be created with an enforced restriction: to follow the classic model.

NetCDF-4 files can be created with the CLASSIC_MODEL flag. This enforces the rules of the classic netCDF data model on this file.
```
      if (nc_create(FILE_NAME, NC_NETCDF4|NC_CLASSIC_MODEL, &ncid)) ERR;
```
Once a classic model file, always a classic model file. This sticks with the file and there is no way to change in within the netCDF API.
Classic model files don't use any elements of the expansion of the data model in netCDF-4. They don't have groups, user-defined types, multiple unlimited dimensions, or the new atomic types.
Since they conform to the classic model, they can be read and understood by any existing netCDF software (as soon as that software upgrades to netCDF-4 and HDF5 1.8.0).
NetCDF-4 features which don't affect the data model are still available: compression, parallel I/O.