How can I pass an ASCIIZ array to a dll?

[Michael Rich]

I need to pass a single dimension string array from IBASIC to a dll created with PowerBASIC. I believe IBASIC uses ASCIIZ strings.

Tried lots of different things, but can’t get it to work.

BTW - Passing a single string variable from IBASIC to the function in the PowerBASIC dll works using ASCIIZ.

Help.

Thanks,

Michael Rich

[Chris Holbrook]

Does the IBASIC function pass the array on the stack, or does it allocate memory and pass a pointer to it? And does it pass an array of fixed-length asiz strings, or an array of DWORD pointers?

[Michael Mattias]

"Array" to PowerBASIC means something special... a PB-proprietary array descriptor is passed on the stack by reference.

If IBasic is passing an array, it could be what Windows would pass for an "array of null-teminated strings" : a contiguous block of memory with individual strings delimited by $NUL (CHR$(0)) with an additional $NUL at the end.

In this case you will have to PARSE out that string into elements; your function will probably use the address of the memory block as its parameter.

But Ibasic might be passing an array of OLE string handles. In that case it is probably passing the address of a block of memory containing those strings, and you could use in your procedure...

FUNCTION foo ( BYVAL addr AS DWORD, BYVAL nEl AS LONG) EXPORT AS LONG

 LOCAL S() AS STring
 REDIM S (nEl-1) AT addr 

..

.. to use a string array.

It all depends what iBasic is actually passing. If it's not some kind of proprietary descriptor, writing your function to handle it will be really straightforward.

But ya gots to know what iBasic is passing.

MCM

[Michael Rich]

Thanks for the reply MCM.

I tried you're suggested code and it crashed.

You're right - "But ya gots to know what iBasic is passing" - if we lnew what it was passing then anyone could be a clever programmer! I checked their documentation - couldn't find the answer. IBASIC is no longer supported - that's one of the may reasons I just switched to PowerBASIC.

Any suggestions on how to attack this by trial and error?

Thanks again,

Michael

[Michael Rich]

Chris - all good questions - but that's the problem, I checked the IBASIC documentation and I am unable to find the answers. So it is all trial and error. So far, all my trials have been errors.

Thanks,

Michael

[Kev Peel]

This might work for the array:

Function TestFunc(ByVal pArr As DWORD PTR) As Long
 
' Method one (comment out to disable)
local pszStr As Ascii Ptr
pszStr = @pArr[0] ' First array element
? @pszStr
pszStr = @pArr[1] ' Second array element
? @pszStr
 
' Method two (comment out to disable)
local pszStr As Ascii Ptr
pszStr = pArr ' First array element
? @pszStr
pszStr = pArr + 4 ' Second array element
? @pszStr
 
End Function

If the above doesn't work either then odds are it's using an array descriptor instead of actual pointer locations. It can be very difficult to discover the format of a descriptor if you don't have a definition for it.

[Walt Thompson]

Hi Michael;

According to the PB ASCIIZ documentation PB passes ACSIIZ strings by reference. That is the pointer to the ASCIIZ data is passed to the called function, not the actual data. Does IBASIC expect the actual data?

If IBASIC expects the data, then you could create a standard string, append a $NUL to it, and pass it to IBASIC.

[Michael Rich]

Hi Walter;

I just need to get the array strings FROM IBASIC into the PB dll. I do NOT need to modify strings and pass them back to IBASIC.

Michael

[Chris Holbrook]

if you have the address of the array then you can examine memory at that address and get clues, particularly if you know what kind of data to expect. Warning - if you try to examine memory to which you do not have access, you will GPF!

you may find this viewer useful, given the address of the array.

[Michael Rich]

Kev,

You got me going in the right direction and using a modification to your Method two, I got it to work!.

See below:

LOCAL pszStr AS ASCIIZ PTR
pszStr = pArr ' First array element
? @pszStr
pszStr = pArr + 255 ' Second array element
? @pszStr
pszStr = pArr + 510 ' Third array element
? @pszStr

Kev - thanks again for all your help, and thanks to all who took the time to reply.

Michael

[Kev Peel]

Michael,

No problem, glad to help

You may want to use a size variable or constant to reference the array elements (if the size changes) by using arithmetic, ie: pszStr = pArr + (255 * element).

Another method is a UDT pointer:

TYPE STR_ELEMENT
     szElement As Asciiz * 255
END TYPE
 
LOCAL pEle AS STR_ELEMENT PTR
pEle = pArr
 
? @pEle[0].szElement ' First array element

[Michael Mattias]

If the strings are not all the same length (or if they are) you can advance the pointer dynamically by getting the length of each piece......

pszStr = pArr ' First array element
? @pszStr
pszStr = pszStr  + Lstrlen(BYVAL pszStr) + 1 
? @pszStr
pszStr = pszStr  + Lstrlen(BYVAL pszStr) + 1 
? @pszStr 
...