Previous: Basic FITSIO Conventions
Up: Basic FITSIO Conventions
Next: Subroutine Names
Previous Page: Basic FITSIO Conventions
Next Page: Subroutine Names

Current Header Data Unit (CHDU)

A basic concept used throughout this interface is that of the Current Header Data Unit (CHDU). When a FITS file is first opened, the CHDU is defined to be the primary header and data array (i.e., the first HDU in the FITS file). Subroutines are provided to move to other HDUs within the FITS file or to append a new HDU to the end of the FITS file. The other subroutines which read or write header keywords or data values always operate only within the CHDU.