Creating a CDF5 file without writing any data in it creates a "classic" CDF1 file

[krisfed]

I am creating and immediately closing a netcdf file with NC_FORMAT_CDF5/NC_FORMAT_64BIT_DATA (without creating any dimensions, variables, attributes, etc.). When I query the format, it returns 1 (NC_FORMAT_CLASSIC). Is this expected?

This is on a mac (Apple Silicon). NetCDF version is 4.9.3 and the build log shows that CDF5 is enabled:

# Features
--------
Benchmarks:		no
NetCDF-2 API:		yes
HDF4 Support:		no
HDF5 Support:		yes
CDF5 Support:		yes
NC-4 Parallel Support:	no
PnetCDF Support:	no

Here is the reproduction code:

#include <iostream>
#include <netcdf.h>

void checkErrorCode(int status, const char* message){
    if (status != NC_NOERR){
        std::cout << "Error code: " << status << " from " << message << std::endl;
        std::cout << nc_strerror(status) << std::endl << std::endl;
    }
}


int main()
{
    int ncid;
    int retval;
      
    std::cout << "NC_FORMAT_64BIT_DATA: " << NC_FORMAT_64BIT_DATA << std::endl;

    retval = nc_create("myfile.nc", NC_FORMAT_64BIT_DATA, &ncid);
    checkErrorCode(retval, "nc_create");
    
    int format;
    retval = nc_inq_format(ncid, &format); 
    checkErrorCode(retval, "nc_inq_format");
    
    std::cout << "format: " << format << std::endl;
    
    retval = nc_close(ncid);
    checkErrorCode(retval, "nc_close");
    
}

It produces the following output:

$ ./a.out 
NC_FORMAT_64BIT_DATA: 5
format: 1