Arrays

Arrays are an extension of simple data types. In addition to the type code and VARFLAGS field, there is an additional segment called ARRAY_DESC, which describes the structure of the array:

Format: TYPEDESC_ARRAY        (type descriptor for arrays)

Type

Name

Description

LONG

TYPECODE

IDL variable type code

LONG

VARFLAGS

Bit flags for a type descriptor, OR'd as follows:

'02'x	System variable
'04'x	Array
'10'x	Unknown?
'20'x	Structure (UNSET for simple array)

ARRAY_DESC

--

Array descriptor segment

An array descriptor structure is a fixed-length segment describing the dimensions of the array.

Format: ARRAY_DESC        (array descriptor)

Type	Name	Description
LONG	ARRSTART	Indicates start of array descriptor (= 8)
LONG	NBYTES_EL	Number of bytes per element of the array? (string= 12)
LONG	NBYTES	Number of bytes in array
LONG	NELEMENTS	Number of elements in array
LONG	NDIMS	Number of dimensions in array
LONG$\times$2	--	Unknown (= [0,0])
LONG	NMAX	Number of stored dimensions (always 8?)
LONG$\times$NMAX	DIMS	Dimensions of array, padded with 1s to NMAX

NOTES: The ARRAY_DESC descriptor indicates the size of the array in a number of different manners. The total number of elements is given by the NELEMENTS field. The number of dimensions in the array is given by NDIMS. Even if NDIMS is less than 8, the array descriptor always appears to contain NMAX (=8) stored dimensions. The ``unused'' dimensions are padded with values of 1. The fields NBYTES_EL and NBYTES appear to be unused by readers. There is some evidence that setting these fields to values of 0 does not harm the readers' ability to parse the file.