Problem calling PB DLLs from VB

[Robert Keith]

Hi All,

I am trying to write a series of DLLs to be called by VB 2008 apps as well as VBA code in Excel and Access. I have had some success but I have been unable to pass any more than one variable to a function in a DLL. If I try to pass more than one then VB6/VBA just crashes and VB2008 gives the error message "Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

I have tried every possible combination of passing variables ByVal and ByRef. The DLLs work fine when called from a PB application.

I have got to a stage where I need to emulate some legacy functions that pass variables as ByRef arrays. Here is an example of the DLL code:
----------------------
#COMPILE DLL
#DIM ALL
%USEMACROS = 1
#INCLUDE "Win32API.inc"
FUNCTION BRfunc ALIAS "BRfunc"(BYREF Int0 AS INTEGER, BYREF Arr1() AS BYTE, BYREF Arr2() AS STRING, BYREF Int1 AS INTEGER) EXPORT AS LONG
DIM i AS INTEGER
DIM tStr AS STRING
FOR i = 0 TO Int0
tStr = Arr2(i)
Arr2(i) = STR$(arr1(i)) & " " & tStr
NEXT
Int1 = i-1
FUNCTION = i
END FUNCTION
------------------------------------
And here is the Powerbasic code that calls it:
------------------------------------
#COMPILE EXE
#DIM ALL
DECLARE FUNCTION BRfunc LIB "ByRefDll.dll" ALIAS "BRfunc" (BYREF Int0 AS INTEGER, BYREF Arr1() AS BYTE, BYREF Arr2() AS STRING, BYREF Int1 AS INTEGER) AS LONG
FUNCTION PBMAIN () AS LONG
DIM Rint AS INTEGER
DIM Rlng AS LONG
DIM Rstr AS STRING
DIM i AS INTEGER
DIM AnimalQty(5) AS BYTE
DIM AnimalName(5) AS STRING
AnimalQty(0) = 5
AnimalName(0) = "snakes"
AnimalQty(1) = 3
AnimalName(1) = "emus"
AnimalQty(2) = 23
AnimalName(2) = "sheep"
AnimalQty(3) = 202
AnimalName(3) = "caterpillars"
AnimalQty(4) = 7
AnimalName(4) = "elephants"
AnimalQty(5) = 2
AnimalName(5) = "horses"
Rlng = BRfunc(5, AnimalQty(), AnimalName(), Rint)
Rstr = STR$(Rlng) & " types of animals:"
FOR i = 0 TO Rint
Rstr = Rstr & CHR$(13) & AnimalName(i)
NEXT
MSGBOX Rstr
END FUNCTION
----------------------------------
This works fine in PowerBasic. The same code in any VB does not work. Attached are some code examples in VB6 and VB 2008 that demonstrate the problem.

Can anyone please let me know where I am going wrong.

Thanks in advance,

Rob

[Mike Doty]

Not sure how byte arrays are passed, but this how string arrays are passed.
See page 634 of manual on SafeArrays

Here is the bulletin board codes for posting code:
http://www.powerbasic.com/support/pb....php?do=bbcode
It is also at the bottom of the page under BB code

The word "code" within brackets to start a code block, /code within brackets to end code block.

#INCLUDE "Win32API.inc"
#INCLUDE "VBAPI32.INC" 
 
FUNCTION BRfunc ALIAS "BRfunc"(Int0 AS INTEGER,  Arr1() AS BYTE,  pSA AS DWORD,  Int1 AS INTEGER) EXPORT AS LONG
 
  DIM i AS LONG
  DIM tStr AS STRING
 
  LOCAL l AS LONG
  LOCAL u AS LONG
  LOCAL vb AS DWORD
  l  = vbArrayLBound(psa,1)
  u  = vbArrayUBound(psa,1)
  vb = vbArrayFirstElem(psa)
  DIM arr2(l TO u) AS STRING AT VB
 
  FOR i = l TO u
    tStr = Arr2(i)
    Arr2(i) = "Not sure here" + STR$(i)
   NEXT
   Int1 = i-1
 
  FUNCTION = i
END FUNCTION

[John Petty]

All arrays in VB are SafeArrays which is not the PB default, they can be read in PB a couple of different ways. The STRING array has an additional problem in that the strings will/may be in Unicode again not a PB default. I add the word "may" as in some cases VB6 (haven't used 8) will attempt ,not always successfully, to convert to ANSII strings from Unicode i.e if you have an array of fixed length strings inside a UDT it would convert only the first array member.

[Robert Keith]

Thanks

Thanks for the replies. After a couple of tries I was able to do what I need. The array of strings are not required. I tried it because I had previously struck problems passing string variables. This application requires arrays of unsigned integers so the example on page 634 showed the way.

I had not got as far as Appendix B on page 632 of the manual. It explains the problems I was having.

Lets see if I get this right:

#COMPILE DLL
#DIM ALL
FUNCTION BRfunc ALIAS "BRfunc"(BYVAL Arr1 AS DWORD, BYVAL Arr2 AS DWORD, BYVAL Int0 AS LONG) EXPORT AS LONG
DIM Brr1(Int0) AS LONG AT Arr1
DIM Brr2(Int0) AS LONG AT Arr2
DIM i AS LONG
DIM j AS LONG
DIM k AS LONG
    FOR i = 0 TO Int0
        j = Brr2(i) * Brr1(i)
        Brr1(i) = j
        k = k + j
    NEXT
    FUNCTION = k
END FUNCTION

Thanks again,

Rob

[José Roca]

If Int0 is the number of elements of the array, it should be:

#COMPILE DLL
#DIM ALL
FUNCTION BRfunc ALIAS "BRfunc"(BYVAL Arr1 AS DWORD, BYVAL Arr2 AS DWORD, BYVAL Int0 AS LONG) EXPORT AS LONG
DIM Brr1(Int0-1) AS LONG AT Arr1
DIM Brr2(Int0-1) AS LONG AT Arr2
DIM i AS LONG
DIM j AS LONG
DIM k AS LONG
    FOR i = 0 TO Int0-1
        j = Brr2(i) * Brr1(i)
        Brr1(i) = j
        k = k + j
    NEXT
    FUNCTION = k
END FUNCTION

[Robert Keith]

Thanks again

Thanks José. I had better do as you suggest in order to reduce confusion. That is a similar convention to some other DLLs I work with.

Regards,

Rob