Re: Referencing a row in a two dimensional array

"SmallHairyTroll <[email protected]>" <[email protected]> writes:

> This is a newbie question, but I can't find an answer in my Lisp 
> text:
>
> I have a two dimensional array (MAKE-ARRAY `(,row ,col)). Currently 
> I am writing binary data to this array a single byte at a time using 
> READ-BYTE from within two nested loops (row & column loops).
>
> I now want to use READ-SEQUENCE to read a chunk of bytes into each 
> row, but I'm stumped as to how I can give READ-SEQUENCE a reference 
> to just the row of the array. This is easy to accomplish in C using 
> pointers, and I am sure it is just as easy in Lisp.
>
> (READ-SEQUENCE (row-reference-here) in-stream 0 row)
>

Have a look at the :displaced-to argument to make-array.  See
<URL:http://www.lispworks.com/reference/HyperSpec/Body/f_mk_ar.htm>
for the details.  With this, you can make a second array that "points
to" a subset of your original array (Sorry for the sloppy wording).

Note that you can't do arbitrary slices, only in row-major order.

Regards,

Rudi
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