Open a FITS file whose primary array represents a spectrum table (flux vs wavelength) and dump its columns 
 
void FITS_tutorial6()
{
   
   
 
 
   
   TFITSHDU hdu(dir + 
"/fitsio/sample4.fits[1]");
 
 
   
   const auto nColumns = hdu.GetTabNColumns();
   printf("The table has %d columns:\n", nColumns);
   for (
auto i : 
ROOT::TSeqI(nColumns)) {
 
      printf(" - Column %d: %s\n", i, hdu.GetColumnName(i).Data());
   }
}
FITS file interface class.
 
This file contains a specialised ROOT message handler to test for diagnostic in unit tests.
 
   
The table has 8 columns:
 - Column 0: objId
 - Column 1: ra
 - Column 2: dec
 - Column 3: mag
 - Column 4: reddening
 - Column 5: objType
 - Column 6: mu_ra
 - Column 7: mu_dec
- Author
 - Claudi Martinez 
 
Definition in file FITS_tutorial6.C.