Attributes

This page describles procedures handling NetCDF attributes.

See the improvements page for an explanation of the mnemonics “basic change”, “interface change”, “functionality change”, “additional procedure”.

nf95_copy_att

(basic change)

  subroutine nf95_copy_att(ncid_in, varid_in, name, ncid_out, varid_out, ncerr)
    integer, intent( in):: ncid_in,  varid_in
    character(len=*), intent( in):: name
    integer, intent( in):: ncid_out, varid_out
    integer, intent(out), optional:: ncerr

Reference: nf90_copy_att

nf95_get_att

(functionality change)

  subroutine nf95_get_att(ncid, varid, name, values, ncerr)
    integer,                          intent( in) :: ncid, varid
    character(len = *),               intent( in) :: name
    character(len = *), integer(any kind) or real(any kind), intent(out) :: values
    integer, intent(out), optional:: ncerr

nf95_get_att is more secure than nf90_get_att. For an argument values of type character, nf95_get_att checks that the values argument is long enough and removes the null terminator, if any. For a numeric scalar values argument, nf95_get_att checks that the attribute contains a single value.

Reference: nf90_get_att

nf95_get_missing

(additional procedure)

subroutine nf95_get_missing(ncid, varid, missing)

  integer, intent(in)::  ncid, varid

  real or double precision or integer, of any kind, or character, intent(out):: missing
  ! missing or fill value

The procedure returns the missing_value or _FillValue attribute if one of them is present, else the nf95_fill_type constant corresponding to the type of argument missing. If both missing_value and _FillValue are present then the procedure checks that they are equal.

If the type of the missing_value or _FillValue attribute is different than the type of argument missing then conversion will occur. The procedure prints a warning as this is dangerous usage. Indeed, if you read values of the corresponding NetCDF variable without conversion then the converted missing value from the attribute may not correspond to the un-converted value in the NetCDF variable. And if you read values of the NetCDF variable with the same conversion as for the attribute, then values which are valid but close to the missing value in the NetCDF variable may become equal to the missing value after conversion. See the (admittedly contrived) examples in file Tests/test_get_missing.f90 which demonstrate this risk. Concluding advice: if you convert missing value from double precision real to single precision real, for example, be sure to convert also values of the NetCDF variable, and make sure that there are no values close to the missing value in the NetCDF variable.

nf95_inq_attname

(interface change)

subroutine nf95_inq_attname(ncid, varid, attnum, name, ncerr)

  integer, intent(in):: ncid, varid, attnum
  character(len = :), allocatable, intent(out):: name
  integer, intent(out), optional:: ncerr

The argument name has dynamic (deferred) length in nf95_inq_attname instead of assumed length in nf90_inq_attname. So you do not have to worry about a maximum length for the corresponding actual argument: just declare it also as character(len = :), allocatable.

nf95_inquire_attribute

(interface change)

subroutine nf95_inquire_attribute(ncid, varid, name, xtype, nclen, attnum, &
     ncerr)

  integer, intent( in)     :: ncid, varid
  character (len = *), intent( in)     :: name
  integer, intent(out), optional :: xtype, nclen, attnum
  integer, intent(out), optional:: ncerr

The argument for the number of values or characters of the attribute is called nclen in nf95_inquire_attribute, instead of len in nf90_inquire_attribute. len is not a good choice for a variable name because it is the name of a Fortran intrinsic procedure.

Reference: nf90_inquire_attribute

nf95_put_att

(basic change)

subroutine nf95_put_att(ncid, varid, name, values, ncerr)
  integer, intent(in) :: ncid, varid
  character(len = *), intent(in) :: name
  character(len = *) or integer(any kind) or real(any kind), intent(in) :: values
  integer, intent(out), optional:: ncerr

Reference: nf90_put_att