Q48401: Multi-DIMensioned Arrays Are in Column Order; BC /R Row Order

Article: Q48401
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890801-7 B_BasicCom | mspl13_basic
Last Modified: 28-DEC-1989

By default, multidimensional arrays are stored in contiguous columns
in memory (that is, column-major order) in compiled BASIC. With
column-major order, the leftmost subscript (the row dimension)
changes the fastest.

You can force executable .EXE programs to store arrays in rows by
using the BC /R option. However, the /R option (for row-major order)
is not available in the QB.EXE or the QBX.EXE editor environment. With
row-major order, the rightmost subscript (the column dimension)
changes the fastest.

This information applies to Microsoft QuickBASIC Versions 4.00, 4.00b,
and 4.50 for MS-DOS, to Microsoft BASIC Compiler Versions 6.00 and
6.00b for MS-DOS and MS OS/2, and to Microsoft BASIC PDS Version 7.00
for MS-DOS.

In the DIM X(row,column) statement, arrays are stored by default in
column order in memory. When looking at a contiguous block of memory
that is storing a two-dimensional array, you'll find one column stored
after another. For example, for DIM X(2,2), the array elements are
stored by default in the following column-major order:

   X(0,0), X(1,0), X(2,0), X(0,1), X(1,1), X(2,1), X(0,2), X(1,2), X(2,2)

If you compile the program with BC /R, you get row-major order, as
follows:

   X(0,0), X(0,1), X(0,2), X(1,0), X(1,1), X(1,2), X(2,0), X(2,1), X(2,2)

An easy way to demonstrate the storage order is to BSAVE a two-
dimensional array and then BLOAD the same data into a one-dimensional
array. You then have a firsthand view of how the array is stored.

Unlike BASIC, Microsoft C defaults to row-major order.

This array-order information is taken from Page 313 of the "Microsoft
QuickBASIC 4.0: Learning and Using" manual for QuickBASIC Versions
4.00 and 4.00b, from Page 313 of the "Microsoft BASIC Compiler 6.0:
Learning and Using Microsoft QuickBASIC" manual for Versions 6.00 and
6.00b, and from Page 560 of the "Microsoft BASIC 7.0: Programmer's
Guide" for BASIC PDS Version 7.00.

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