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CFITSIO is a machine-independent library of routines for reading and writing data files in the FITS (Flexible Image Transport System) data format. CFITSIO is written entirely in ANSI-C and provides the same functions as in the previously available Fortran FITSIO library. This library was written to provide a powerful yet simple interface for accessing FITS files which will run on most commonly used computers and workstations. This version of CFITSIO supports all the features described in the official NOST definition of the FITS format and can read and write all the currently defined types of extensions, including ASCII tables (TABLE), Binary tables (BINTABLE) and IMAGE extensions. The CFITSIO routines insulate the programmer from having to deal with the complicated formatting details in the FITS file, however, it is assumed that users have a general knowledge about the structure and usage of FITS files.

This new ANSI-C library should not be confused with the previously available set of C macros which provide a C-callable interface to the Fortran FITSIO routines. These older macros are contained in the cfitsio.h file that is distributed along with the Fortran FITSIO source files. These macros will continue to be supported for a limited period, but they should be considered obsolete. New FITS application software should be written using the new CFITSIO interface described here.

The CFITSIO package was developed for use by the HEASARC (High Energy Astrophysics Science Archive Research Center) at the NASA Goddard Space Flight Center to convert various existing and newly acquired astronomical data sets into FITS format and to further analyze data already in FITS format. The latest version of the CFITSIO source code, documentation, and example programs are all available on the World-Wide Web at the following URL:
CFITSIO also can be obtained from the HEASARC via anonymous ftp from (or, in the software/fitsio/c subdirectory.

Any questions, bug reports, or suggested enhancements related to the CFITSIO package should be sent to the author:

        Dr. William Pence                 Telephone:  (301) 286-4599
        HEASARC                           E-mail:
        Code 662
        NASA/Goddard Space Flight Center
        Greenbelt, MD 20771
This User's Guide assumes that readers already have a general understanding of the definition and structure of FITS format files. For further information about FITS formats, please obtain a copy of the `FITS User's Guide' and the `NOST FITS Standard', which are available from the NASA, Science Office of Standards and Technology at the address given below. Both of these documents are available electronically from their Web site and via anonymous ftp at in the /pub/fits directory. Any questions about FITS formats should be directed to the NOST, at:

        NASA, Science Office of Standards and Technology
        Code 633.2,
        Goddard Space Flight Center
        Greenbelt MD 20771
        (301) 286-2899
CFITSIO users may also be interested in the FTOOLS package of programs that can be used to manipulate and analyze FITS format files. Information about FTOOLS can be obtained on the WWW at:
or via anonymous FTP at:  /software/ftools/release

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