maplun(3F)

NAME
     maplun - returns the integer file descriptor for a Fortran logical unit
     number

SYNOPSIS
     maplun (lun)
     integer*4 lun

DESCRIPTION
     This function returns the file descriptor given a Fortran logical unit
     number.

DIAGNOSTICS
     Success is indicated by a non-negative return value.  A negative return
     value indicates an error.  The value of errno can be examined to
     determine the cause of the error.

NOTES
     This function cannot be used on indexed files since each Fortran indexed
     file is represented by two physical files and this function cannot map a
     single Fortran logical unit to two file descriptors. Also, the indexed
     file internal format is proprietary and cannot be modified by the user
     directly so this function, or a similar function, will not help in that
     respect.