cfitsio is a library of ANSI C routines for reading and writing FITS format data files. A set of Fortran-callable wrapper routines is also included for the convenience of Fortran programmers. The documentation directory contains a comprehensive API reference guide and instructions on using cfistio in Fortran programs. If you wish to build the library with the --enable-reentrant option, run the SlackBuild script like this: REENTRANT=yes ./cfitsio.SlackBuild This option is disabled by default because some legacy software will not link against reentrant libcfitsio.