I having some memory leaks working with structure pointer used by a DLL external function, that I call within a class used by a dataflex Web Server.
I make several tried and below is only one of the last, but the result is always the same.. All data are correctly read from the structure i using... and can be moved to dataflex string and last to a webform
but after that as soon I do NavigateForward or navigatebackward or repeating another call.. always I get an Access Violation popoup error.

below is a function that is used in this class
// this is the structure
  Struct DMT_INFO_DER_BLOB //     
         Integer  cbData 
        Address  pbData 

// this is the external function
           External_Function dmtGetSignedInfoParam "dmtGetSignedInfoParam" DIMATECDLL ;
	                Integer TimestampParamType ;
	                 Integer dwIndex;
	                  Address  pvData; // pointer to DMT_INFO_DER_BLOB
	                  Address pcbData; 
	               Returns Integer
 // this function is within  cObject base class   "Class cDimatek is a cObject"

  Function GetSingleCertValue   Integer iparamtype      Returns   String
            Integer  dwParamLen  i 
            Address pParam lpserialnumber
            Integer VerifySignedFileResult iret
            DMT_INFO_DER_BLOB pvdata
            String SerialNumber
            Move 0 to dwParamLen
             // this call need to get the lenght alloc memory
            Move (dmtGetSignedInfoParam(iparamtype,  0,0, (addressof( dwParamLen)))) to VerifySignedFileResult
            If (VerifySignedFileResult = DMT_OK) Begin
                Move (alloc (dwParamLen)) to pParam
                Move (AddressOf(pvdata))  to pParam
                Move 0 to SerialNumber

                 // this receive the pointer to the structure that contain the values in pParam
                 Move (dmtGetSignedInfoParam(iparamtype,  0,   pParam, dwParamLen)) to VerifySignedFileResult

                  // fill the string that will receive the value
                  Move (Repeat(character(32), (pvdata.cbData)))   to SerialNumber
                If (VerifySignedFileResult = DMT_OK)       Begin
                    Move (Alloc(pvdata.cbData)) to lpserialnumber

                     Move  (addressof(SerialNumber)) to lpserialnumber

//                   this is how it work with c# to convert a pointer to structure
//                    DMT_INFO_DER_BLOB Param = (DMT_INFO_DER_BLOB)System.Runtime.InteropServices.Marshal.PtrToStructure(
//                        pParam, typeof(DMT_INFO_DER_BLOB));
//                    InforCertDialog.oSIG_SIG_SERIAL_NUMBER.Text = Param.pbData.ToString(); // new string(dimatekCertInfo.SerialNumber)  ;
                        Move (MemCopy(lpserialnumber ,  pvdata.pbData,    pvdata.cbData)) to iret
                          Move (Free (pParam)) to iret
                         Move (Free(lpserialnumber)) to iret
                         Move (Free( pvdata.pbData)) to iret
                            Function_Return SerialNumber  // this is filled right and move back to webserveice

               If (pParam>0)  Move (Free (pParam)) to iret
              If ( pvdata.pbData>0)    Move (Free ( pvdata.pbData)) to iret
              if ( lpserialnumber>0)   Move (Free ( lpserialnumber)) to iret
            Function_Return ""

//this is the function within the webservice that call the function in the object class called owebdimatek 

  { Published=True }
    { Description = "GetSingleCertValue"}
   Function GetSingleCertificateValue   Integer iparamtype      Returns   String
          String svalue
            Get GetSingleCertValue of owebdimatek iparamtype to svalue
            Function_Return svalue

//and this is the function that I call within the event onshow on the webview

     Procedure OnShow
                Forward Send OnShow
                Integer iret isize i
                String  sfinalResult
                     Get  GetSingleCertificateValue  of oDimatecwebservice DMT_SIG_CER_SERIAL_NUMBER to sfinalResult
                   WebSet psValue of  oWebFormsn to sfinalResult   // this is ok the value is showed correctly
                  // but after that everything I will do like example a normal NavigateForward will get AccessViolation popup  see below
As soon I Try a Nabvigatebackward or Navigateforward from the view after the value is correctly showed i get AccessViolation Popoup and the debugger stop here within function CallAction :

  { Visibility=Private }
    Function CallAction tWebRequest Request Returns tWebResponse
        Handle hoTarget
        Integer i icAction
        Boolean bAllowAction bLoadWebApp
        String sObjectName
        tWebResponse Response
        //  Determine if this is the LoadWebApp call
        If (SizeOfArray(Request.aActions) > 0) Begin
            If (Request.aActions[0].sAction = "LoadWebApp") Begin
                Move True to bLoadWebApp
        // Process the Request Header....
        Set pbSynchronizing to True
        Get ProcessRequestHeader Request.Header bLoadWebApp to bAllowAction  <<<<<<<<<
        Set pbSynchronizing to False
I suppose that I missing something but I free the memory any time I used ALLOC I did a lot of try with string uChar and memcopy but the result is always the same I can read all values from the DLL structure POinter parameters but after that seem that the string memory have trouble... that I cannot solve... at this point

II sure that Dataaccess developers can have some suggestion that I missing..Anyway I suggest in the future to can have a Function like C# already have PtrToStructure that allow to get values from a pointer to a structure without take care about memory alloc and free

I don't know if this depend by the way I use to do this call

1.DLL with structures and external function->
2. DF Class cobject where are defined all functions that make direct calls to the dll->
3. webservice that call functions within the DF cobject class
4. webapp mobile view that call the webservice functions that call the class object functions that call the external DLL functions

Franco Spinella