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How can I pass an ASCIIZ array to a dll?

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  • How can I pass an ASCIIZ array to a dll?

    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

  • #2
    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?

    Comment


    • #3
      "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...
      Code:
      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 Mattias
      Tal Systems Inc. (retired)
      Racine WI USA
      [email protected]
      http://www.talsystems.com

      Comment


      • #4
        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

        Comment


        • #5
          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

          Comment


          • #6
            This might work for the array:

            Code:
            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.
            Last edited by Kev Peel; 19 Jun 2008, 02:05 PM.
            kgpsoftware.com | Slam DBMS | PrpT Control | Other Downloads | Contact Me

            Comment


            • #7
              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.
              Last edited by Walt Thompson; 19 Jun 2008, 02:18 PM. Reason: spelling correction

              Comment


              • #8
                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

                Comment


                • #9
                  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.

                  Comment


                  • #10
                    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

                    Comment


                    • #11
                      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:

                      Code:
                      TYPE STR_ELEMENT
                           szElement As Asciiz * 255
                      END TYPE
                       
                      LOCAL pEle AS STR_ELEMENT PTR
                      pEle = pArr
                       
                      ? @pEle[0].szElement ' First array element
                      kgpsoftware.com | Slam DBMS | PrpT Control | Other Downloads | Contact Me

                      Comment


                      • #12
                        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......
                        Code:
                        pszStr = pArr ' First array element
                        ? @pszStr
                        pszStr = pszStr  + Lstrlen(BYVAL pszStr) + 1 
                        ? @pszStr
                        pszStr = pszStr  + Lstrlen(BYVAL pszStr) + 1 
                        ? @pszStr 
                        ...
                        Michael Mattias
                        Tal Systems Inc. (retired)
                        Racine WI USA
                        [email protected]
                        http://www.talsystems.com

                        Comment

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