Introduction

What is it?

NetCDF95 is an alternative Fortran interface to the NetCDF library. The official Fortran interface is the Fortran 90 NetCDF interface.

The name NetCDF95 was at first a reference to the Fortran 95 standard but NetCDF95 now uses Fortran 2003 features.

Author: Lionel GUEZ

Why an alternative interface?

Compared to the the Fortran 90 NetCDF interface, NetCDF95 is meant to be friendlier and more secure. Notably:

  • NetCDF95 frees you of the cumbersome task of handling the error status. NetCDF95 procedures behave like the Fortran input/output statements. That is, the error status is an optional output argument. Consider, for example, the Fortran formatted read statement:
    read([unit=]u, [fmt=]fmt [,iostat=ios] [, err=error-label] &
   [,end=end-label]) [list]

If the err, end and iostat keywords are not provided, and there is a problem in the execution of the read statement, then execution of the program stops (with an informative error message from the compiler). Similarly, NetCDF95 procedures have an optional argument for error status. If the optional argument is absent and there is an error, then the NetCDF95 procedure produces an error message and stops the program. (The official Fortran 90 interface looks like it has been made to mimic the C interface, and this is not optimal in Fortran.)

  • NetCDF95 frees you of assumptions on the size of arrays and the size of character strings when you call several inquiry procedures. (It does so by making use of allocatable arguments, a Fortran 2003 feature.) See nf95_inquire_variable, nf95_inq_grpname, nf95_inq_grps, nf95_inq_grpname_full, nf95_inq_attname.

  • NetCDF95 offers procedures that have no counterpart in the official interface. These combine several calls to other NetCDF95 procedures for common higher-level tasks. See nf95_gw_var, nf95_find_coord, nf95_create_single, nf95_get_missing, nf95_gunp_var.

  • NetCDF95 replaces functions by subroutines. Procedures of the official Fortran 90 interface are all functions, and they are all with side effects. First, they have intent(out) arguments. Furthermore, there is obviously data transfer inside the procedures. Any data transfer inside a function is considered as a side effect. In this respect, the Fortran 90 interface mimics the C interface. But Fortran has a different programming style than C and frowns upon side-effects in functions. See for example Metcalf and Reid (Fortran 90/95 Explained, 1999, ยงยง 5.10 and 6.10).

  • NetCDF95 provides the procedure nf95_inq_varnatts, corresponding to the strangely missing nf90_inq_varnatts in the official Fortran 90 interface.

  • There are other improvements such as securing the call to nf95_get_var by checking the arguments start and count_nc, and renaming badly chosen argument names len and count to nclen and count_nc.