Calling C-DLL from 2.0

Help !!

I trie to call a function from a DLL called scom32. The DLL is written in MSVC++ 4.00 and i only have the headerfile. I have converted the headerfile to delphi and try to call the funtion. But something goes wrong with i think passing the function arguments. When the function i call only has one argument then the call works, but when i have two or more
arguments the call actualy changes arguments wich normally would't change.

Here is what i did:

-------------- C-header:

typedef struct tagPCDCONN
      int       Port;
      int       Protocol;
      int       Baud;
      BYTE         Sbusmode;
      BOOL        bEPROM;
      BYTE        TxMsg[270];


int WINAPI PcdComOpen(LPCONN);

-------------- This is my DELPHI equivalent:

 PCDCONN = Record

      Port      :Integer;
      Baud      :Integer;
      bEPROM      :Longbool;
      TxMsg      :Array[0..269] of Byte;


 Version: Array [0..127] of AnsiChar;
 Status : Integer;

function PcdComOpen(LPCONNEC:PCDCONN):Integer;
 far; pascal; external 'SCOM32';
function PcdRdVersion(LPCONNEC:PCDCONN;Version:PChar):Integer;
 far; pascal; external 'SCOM32';
-------------- And so i call the functions --------
 status:=PcdComOpen(PCDCONN^);           {1}
 status:=PcdRdVersion(PCDCONN^,Version); {2}

When i check what is returned in the status then i can only say it works correct (in statement {1} as well in {2}). But in statement {2} the result in 'version' is wrong and 'PDCONN' value's are destroyed. Only the first two fields are not correct anymore, so i suspect it has something to do with memory allocation or with passing the function arguments. I have searched for two days but can't seem to find out what the problem is.

Is there anyone who can help me !!!

Kind Regards,

Rene Reuscher, ANTONIUS Vessel heads        
Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

I think that you should first change your calling convention in your declaration of the routines PcdComOpen and PcdRdVersion. If you are trying to use a Win32 DLL the calling convention should stdcall so your routines should look like :
function PcdComOpen(LPCONNEC:PCDCONN):Integer;
                     stdcall; external 'SCOM32';
                    function PcdRdVersion(LPCONNEC:PCDCONN;Version:PChar):Integer;
                     stdcall; external 'SCOM32';

The problems that you describe could be caused by a wrong calling convention. You must test it to make sure that I have given you the correct answer.
You defined the functions as follows:

function PcdComOpen(LPCONNEC:PCDCONN):Integer;
                   far; pascal; external 'SCOM32';
                   far; pascal; external 'SCOM32';

You have used the "pascal" keyword which sets the calling convention to pascal-style. The DLL was written in C so you need to use "C-style" calling convention i.e.  "stdcall".

Fixed declarations:

function PcdComOpen(LPCONNEC:PCDCONN):Integer;
                   far; stdcall; external 'SCOM32';
                   far; stdcall; external 'SCOM32';


Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
rene041697Author Commented:
I had tried 'stdcall' already because C++ says that 'WINAPI is equivalent with far_pascal, pascal. But anyway i tried it again, and still got the same result: I get an error message -->

 'Raised exception class EaccessViolation with message 'Access     violation at adress 0000009. Read of address 709F9147'

I tried this also with the other calling conventions like 'register','cdecl'. But 'pascal' was the only one were i didn't got this error message.
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.