Hi,

I have a Symbol mobile device with an integrated barcode scanner. The scanner's API in C and I cannot use every API calls.

An example: The problem appears in the
ScanBuffer:=SCAN_AllocateBuffer(TRUE,dwScanSize);
line (see the test app below).
If I run in GDB the error message is:

warning: Prefetch Abort: Thread=8dcfe8dc Proc=8c329ab0 'project1.exe' warning: AKY=00004001 PC=00000000 RA=00011338 BVA=00000000 FSR=000004f0

Program received signal SIGSEGV, Segmentation fault. 0x00000000 in ?? ()

The test app is:

program test;
{$apptype console}
{$PACKRECORDS C}
uses Windows, dynlibs;
const
   MAx_SRC=32;
   dwScanSize:DWORD=7095;
type
   STRUCT_INFO=record
     dwAllocated:DWORD;
     dwUsed:DWORD;
   end;
   LABELTYPE = DWORD;
   LPSCAN_BUFFER = ^SCAN_BUFFER;
   SCAN_BUFFER=record
     StructInfo:STRUCT_INFO;
     dwDataBuffSize:DWORD;
     dwOffsetDataBuff:DWORD;
     dwDataLength:DWORD;
     dwTimeout:DWORD;
     dwStatus:DWORD;
     bText:BOOL;
     dwLabelType:LABELTYPE;
     dwRequestID:DWORD;
     TimeStamp:SYSTEMTIME;
     dwDirection:DWORD;
     szSource:array[0..MAx_SRC-1] of TCHAR;
     blsMultiPart:BOOL;
     dwScanID:DWORD;
     dwBarcodeID:DWORD;
     dwNumRemaining:DWORD;
     dwOffsetAuxDataBuff:DWORD;
     dwAuxDataLength:DWORD;
   end;
   T_SCAN_AllocateBuffer = function
(bText:BOOL;dwSize:DWORD):LPSCAN_BUFFER; cdecl;
var
   SCAN_AllocateBuffer: T_SCAN_AllocateBuffer;
   DLL_Handle:TLibHandle;
   ScanBuffer:LPSCAN_BUFFER;
begin
   DLL_Handle:=LoadLibrary('SCNAPI32.DLL');
   Pointer(SCAN_AllocateBuffer):=GetProcedureAddress(DLL_Handle,
'SCAN_AllocateBuffer');
   ScanBuffer:=SCAN_AllocateBuffer(TRUE,dwScanSize);
   UnloadLibrary(DLL_Handle);
end.

Thanks!

Gabor

Can you show us the c declaration of the function you are calling? It should be on a .h file.

Also, you should put an way to verify if the calls are working, like:

    DLL_Handle:=LoadLibrary('SCNAPI32.DLL');
    if DLL_Handle = nil then raise EException.Create('Could not load library');
    Pointer(SCAN_AllocateBuffer):=GetProcedureAddress(DLL_Handle,
 'SCAN_AllocateBuffer');
    if Pointer(SCAN_AllocateBuffer) = nil then raise
EException.Create('Could not load procedure');

One possibility is that this C library uses name mangling, and the function has a different name from the canonical one. You can check all function names exported by the function using this software:

http://wiki.lazarus.freepascal.org/Libview

I would be very surprised to see that a Windows DLL uses cdecl; as calling convention. Try changing this to

  T_SCAN_AllocateBuffer = function (bText:BOOL;dwSize:DWORD):LPSCAN_BUFFER; stdcall;

Michael.

Many thanks Felipe, the problem is the exported name(s). The exported names is SCAN_AllocateBuffer_A and SCAN_AllocateBuffer_W.

Thanks again!

Gabor

Felipe Monteiro de Carvalho írta:

this happens because windows API code usually have two versions: an Ascii version where chars are 8-bit ASCII (with the suffix A, and used mainly in 9x code) and other where the chars are 2-byte unicode chars with the W suffix, used mainly in 2000/XP stuff (guess W means wide in the sense of widestring)