Gurus,

I have a simple question which I am too tied up to investigate at the
moment.

Q)  When using 'dynamic arrays' in VB, does VB intelligently use pointers
under the hood in a fashion similar to a C/C++ linked lists implementation
or does it allocate contiguous space (a potential nightmare when dealing
with an unknown large amount of data at runtime)?  This makes a world of
difference when Redimming a thousand times...

Thanks for the knowledge.

Shawn

PS.  I think that this 'Karl' and 'Damit' should co-develop a website or
something.  It would be a riot!!!

Shawn,

I've always understood that it is contiguous memory (analagous to the old
malloc/realloc pair of functions).  If I'm filling a large array therefore I
tend to use redim sparingly.  I find the following works for me:

    dim nTop%
    dim nSz%

    dim Things() as MyThings

    nTop% = -1
    nSz% = -1

    do
        if ThingIsToBeAdded() Then
            nSz% = nSz% + 1
            if nSz% > nTop% then
                nTop% = nTop% + 100
                redim preserve Things(nTop%) as MyThings
            end if
            with Things(nTop%)
                . . . .
            end with
        end if
    loop until Finished

    if nSz% >= 0 then redim preserve Things(nSz%) as MyThings

HTH

Peter

I too would be interested in the answer to your array question.

And I too have given up watching soaps on TV after finding the Karl & Gromit
show!

Bertie

Hi

 The Visual Basic Programmers Journal April 1998 issue had a great article
on how VB manages strings and arrays (see black belt programming article
'Play VB's Strings').

 From what I understood of the article, VB allocates a descriptor (4 bytes)
for each string (and also in a dynamic array) - the actual memory is not
allocated for the string until the first string assignment takes place. The
article showed how to increase VB's string handling speed (sometimes up to a
dozen times faster), by playing around with the descriptors using the VarPtr
and StrPtr VB commands (along with the tried and trusted
RTLMoveMemory/CopyMemory api call).

Hope that helps

Chris Eastwood
Software Engineer
ACNielsen Ltd

Chris,

Indeed, I found your suggestion very informative and generally helpful.
However, I am asking about the implementation of dynamic array storage, not
about the storage of strings (either in arrays or not).  Also, I'm not
necessarily always using dynamic arrays for strings.  Many times, I am
holding pointers to objects, complex nested user types, etc...

So again I ask,

"When using 'dynamic arrays' in VB, does VB intelligently use pointers
under the hood in a fashion similar to a C/C++ linked lists implementation
or does it allocate contiguous space (a potential nightmare when dealing
with an unknown large amount of data at runtime)?  This makes a world of
difference when Redimming a thousand times..."

Thanks for any help,

Shawn Woods

You should be able to determine this using the Varptr function for the first
element of the array before and after the redim (preserve ??). My
recollection is that VB maintains contiguous arrays and that REDIM is very
inefficient. The article mentioned in the previous post covers both arrays
and strings. (I also recall a similar article on collections which showed
that you could write a collections class in VB which is more efficient than
using native VB collections! )

/Ian

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