Using [ ] notation

[Dave Biggs]

In the following, the square brackets are used to access the four Bytes that comprise a 32 Bit value.

DIM p AS BYTE Ptr
..
a$ = USING$("#_.#_.#_.#", @p, @p[1], @p[2], @p[3])
..

What is the terminology that describes the square bracket '@p[n]' notation used?

What I understand, from code samples that I have cut 'n pasted or read in PB's Help:

The [n] value is an offset from an address. The size of the offset is n*(Sizeof(variable type that p points to)).
Is that right?

There are a number of examples that use this notation scattered around in PB's Help topics but I didn't locate an actual description of its use yet.
Maybe it's just too basic

[Peter Jinks]

Pointers to arrays

Hi Dave,

I think the "Pointers to arrays" topic might help.

Regards,

Pete.

[Dave Biggs]

Thank you Peter, that was indeed the topic I should have found!

"Pointer Indexing" - now I can put a name to it

[John Gleason]

What is the terminology that describes the square bracket '@p[n]' notation used?

That's a helpful link Peter, it's called "Pointer Indexing" and each would be called an index pointer.

And your formula looks correct Dave, eg.

@xPtr[3] = 3     ' same as x%(3)

assuming xPtr is an INTEGER POINTER set to x%(0)

[Michael Mattias]

>Maybe it's just too basic

No such thing.

[Kerry Farmer]

I think this point raises a very real issue

If you do not know the 'jargon' on a point you want to look up, where do you start? [Its like using an old fashioned dictionary to check the spelling!]

I find this extremely infuriating in Microsoft Office. I think that Office has actually defined the jargon - or at least extended its use - and I just do not know where to go. Especially in the formatting aspects.

What I would like to see is some overall jargon buster paper with screen dumps and little arrows "naming the parts"

PowerBasic goes someway towards this aim with the Command Summary - but perhaps there are other places where a nice Visio diagram would help people like me who have both the ignorance and the great difficulty that I ofetn get the wrong slant on an explanation for mildly ambiguous statements.

Maybe this suggestion should go in the PB listens thread.

[Fred Harris]

pointers

quite awhile ago i posted some examples of that sort of thing that are fairly short example programs...

http://www.powerbasic.com/support/pbforums/showthread.php?t=25165&highlight=Pointers

[Michael Mattias]

Re jargon..... I call the "[]" syntax "pointer offsets;" "()" used with arrays are "subscripts" , not indexes.

[Gösta H. Lovgren-2]

What is the terminology that describes the square bracket '@p[n]' notation used?

Squindex(es).

===========================================
"What do you take me for, an idiot?"
General Charles de Gaulle (1890-1970),
when a journalist asked him if he was happy
===========================================

[Dave Biggs]

Thanks guys. I reckon that I feel a lot more comfortable with the use of that (Squindex) notation now.

I believe I shall think of it as "Pointer Offset Indexing" such that..

The [n] value of each 'Indexed Pointer' is an index to a range of Offset Addresses where..

Offset Address = (Base Address) + [n * sizeof(data element)] bearing in mind that..

n = 0 TO (Length of Target Data \ Length of Data Element) and that..

GPF = [n * Data Elements] > too many

[Michael Mattias]

>>GPF = [n * Data Elements] > too many

Actually, it's

GPF = [n * (Data Elements-1)] > too many

(Pointer offsets are zero-based).

[Dave Biggs]

>(Pointer offsets are zero-based).

n is zero based..