Limitation On The Size Of A Sub?

[Tianyi Zhai]

Hi, there,

The program I wrote calls a Sub in a DLL
that is compiled with PB/DLL v.5.

A user is required to fill in the sub with
all the code he wants, mainly lots of
math calculation. Since the users are not
programmer oriented, they ask to use Undeclared
variables in the sub, which means they are
default as Local-type

Now, for one user, the code in the sub has more
than 5000 lines, around 1000 local double-type
variables. It compiled OK with the "DLL does not
require stack allocation" shown on the compile
window.

However, a call to this sub from the VB5 program
causes "Error 28, stack overflow" every time.

So, what are the limits of:
1. number of local variables within a sub/function?
2. number of lines of code within a sub/function?

Any suggestion of working around the "stack overflow"?

Tianyi Zhai


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[Tom Hanlin]

I'd guess that the DLL is using the EXE's stack space, so the limitation
here is probably based on the size of the stack that VB allocates.

Each of your users is compiling programs with PB/DLL...? Do they each own
a copy of PB/DLL, then?

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Tom Hanlin
PowerBASIC Staff

[Tianyi Zhai]

If that's the case, how can the VB stack, be increased?

Yes, we have more than 15 engineers wondering around south-east,
and each of them as a legal copy installed on his pc.

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[Edwin Knoppert]

PB version 5, VB - stack???
Weird
Stack is afaik related to ram+diskmemory

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[Tom Hanlin]

I don't know what size stack VB uses or whether it's possible to change this.
Though, actually, it seems odd that you'd run out of stack space. Possibly your
VB program is dimensioning some large local arrays? Or perhaps there's a
recursion error in the SUB or main program... worth examining.

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Tom Hanlin
PowerBASIC Staff

[Kev Peel]

From my VB6 'programmers guide' (just as clunky as the compiler)...

...the default Visual Basic stack size is 1MB, it may grow beyond this, however...

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Kev G Peel
KGP Software, Bridgwater, UK.
mailto:[email protected][email protected]</A> http://www.kgpsoftware.com

[Peter Scheutz]

Originally posted by Tianyi Zhai:
However, a call to this sub from the VB5 program
causes "Error 28, stack overflow" every time.

Should you maybe (if possible) make a test program in PB that calls the dll, to verify that it is a VB problem?



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Best Regards
Peter Scheutz

[Guest]

Incorrect passing of parameters when calling a DLL will result in out of stack space in VB. Is the DLL function recursive? Can you call it successfully from PB?

Can you post the function definition and an example of exactly how it is called from VB?

[This message has been edited by Ron Pierce (edited June 22, 2001).]

[Tianyi Zhai]

Thank to all for your help!

The VB routine that calls the PB DLL is passing two one-
dimenssion arraies to the PB DLL. These two arraies are
defined inside the VB as PUBLIC.

The sub inside PB/DLL called by VB is defined like:
SUB Performance (PointName() AS STRING, PointValue() AS DOUBLE, BYVAL Points_In_PDB AS INTEGER) EXPORT

This has been working fine for past five years.

Only this time a field engineer wrote a fairly long code for
the SUB Performance. The arraies passed have about 950 elements,
that means there are at least 950 local double-typed variables,
plus some more intermittent ones

There are about 4000 lines of code in this one sub, which are
dealing with math calculation. There are a lots of *, /, ^, SQR,
etc.

I checked the stack loaded by using the VB Stack Viewer. There
were only four VB Sub/Functions loaded in the stack. All these
Sub/Functions are small(less than 50 lines of code, without loop
operation involved). The Stack Viewer showes that the PB/DLL is
the only other Sub in the Stack.

I tried debugging the PB/DLL. The process always jumps to the end
at the middle of the Sub without giving error message.

Right now I am checking the code line by line. Hope to find
something fishing. I will certainly post the result here.

Tianyi Zhai



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[Tianyi Zhai]

Well, I checked the PB/DLL SUB that caused "Stack Over Limit"
error when calling from a VB5 program.

The REASON of the error is the wrong parameters passed to
math functions inside the PB/DLL SUB:

LOG(A): A < 0
SQR(B): B < 0

I wish to thank to everyone who responsed to my original post, you
led me to working on the math code instead of worrying on the
Local/Global.

Tianyi Zhai



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