Processing Callback From DLL

[Doug Gamble]

I'm trying to interface to a third-party DLL to create and
process ZIP files. I can make and extract ZIP files but now
I want to display a progress bar during the processing. The DLL
provides functions to define a callback routine to receive a
message structure. When ever I make a program to process the
callbacks it crashes.

Here are the C header file structures and declares:

#define ETCP_MAX_FILENAME_LENGTH 255

typedef struct tagCOMPINFO
{
   UCHAR ciZipFileName[ETCP_MAX_FILENAME_LENGTH];     /* name of .ZIP file being processed */
   UCHAR ciFileName[ETCP_MAX_FILENAME_LENGTH];        /* name of the file being processed (added to .ZIP, deleted from .ZIP, or whatever) */
   short ciOperation;        /* operation: 0 zip, 1 unzip, 2 delete, 3 test */
   long ciTotalSize;         /* total number of bytes to process */
   long ciCurrentByte;       /* current byte being processed */
   long ciCompSize;          /* compressed size */
   short ciMethod;           /* compression method */
   short ciPass;             /* pass number [1..n] */
   long ciPassSize;          /* total bytes this pass */
   short ciMessageType;      /* message type (status, error, query) */
   short ciMessageCode;      /* message number (if error message) */
   short ciDiskNumber;       /* disk number (for multi-volume query) */
} COMPINFO;

void FAR PASCAL Et4CPrintHook (FARPROC CPrintRoutine);

short CPRintRoutine(COMPINFO CPrintInfo);

Here is what I'm using in PBDLL 6.0:

TYPE COMPINFO
  ciZipFileName AS STRING * 255
  ciFileName    AS STRING * 255
  ciOperation   AS INTEGER
  ciTotalSize   AS LONG
  ciCurrentByte AS LONG
  ciCompSize    AS LONG
  ciMethod      AS INTEGER
  ciPass        AS INTEGER
  ciPassSize    AS LONG
  ciMessageType AS INTEGER
  ciMessageCode AS INTEGER
  ciDiskNumber  AS INTEGER
END TYPE
DECLARE FUNCTION ZipHook CDECL LIB "COMPPL32.DLL" ALIAS "Et4CPrintHook" (BYVAL lpCPrintInfo AS DWORD) AS INTEGER

'
'
'
FUNCTION ZipStatusCallback (CInfo AS COMPINFO) AS INTEGER
   '
   '
   '
   MSGBOX "Callback" & FORMAT$(CInfo.ciCurrentByte)
   
END FUNCTION

I've have not been able to get this to work! I must be
overlooking something but I'm not sure what. Can anyone
please help!

Thanks,

Doug Gamble



------------------

[Michael Purkhardt]

Doug,

Change your function to return a LONG as oppose to an INTEGER.

-Michael-

[Tom Hanlin]

No, the C function is returning a SHORT, which is an INTEGER in
PowerBASIC.

Assuming the C declaration of CPrintRoutine is correct... it
rather looks like the whole COMPINFO structure is being passed
on the stack. Unfortunately, you can't pass a user-defined type
BYVAL in PowerBASIC. What you'd need to do would be to write a
bit of assembly code to pull the parameter off the stack and
to clean up the stack before returning.

I'll see if I can put together an example.

------------------
Tom Hanlin
PowerBASIC Staff

[Tom Hanlin]

And, oh yeah-- I wouldn't be fully confident in the calling
convention here. Given that Et4CPrintHook uses the PASCAL
convention, CPrintRoutine may be intended to follow suit, so
CDECL may not be the right choice.

------------------
Tom Hanlin
PowerBASIC Staff