Hi,
I have following code (almost literally translated from C) :
//--------------------------------------------------------------------------
// Bit utility to read and write a bit in the buffer 'buf'.
//
// 'op'    - operation (1) to set and (0) to read
// 'state' - set (1) or clear (0) if operation is write (1)
// 'loc'   - bit number location to read or write
// 'buf'   - pointer to array of bytes that contains the bit
//           to read or write
//
// Returns: 1   if operation is set (1)
//          0/1 state of bit number 'loc' if operation is reading
//
type
  PByteArray = ^array of byte;

function bitacc(op, state, loc : byte; buf : PByteArray) : byte; {C-code : static SMALLINT bitacc(SMALLINT op, SMALLINT state, SMALLINT loc, uchar *buf)}

var
  nbyt,
  nbit : byte;
begin
nbyt := loc div 8;
nbit := loc mod 8;
if (op = WRITE_FUNCTION) then
  begin
   if state=1 then
    buf^[nbyt] := buf^[nbyt] or ($01 << nbit)
   else
    buf^[nbyt] := buf^[nbyt] and not ($01 << nbit);
   result:=1;
  end
else
  result:=(buf^[nbyt] >> nbit) and $01;
end;

It's called with this code :

bitacc(WRITE_FUNCTION, bitacc(READ_FUNCTION,0,i,@SerialNum[portnum][0]), (i * 2 + 1), @sendpacket[pos])
{C-code :
bitacc(WRITE_FUNCTION, bitacc(READ_FUNCTION,0,i,&SerialNum[portnum][0]), (short)(i * 2 + 1), &sendpacket[pos]);}

Executing the code gives an an access violation exception. What am I doing wrong ?
I included some debugging code and it seems accessing buf^[nbyt] is the problem.

TIA
Koenraad Lelong.

"array of byte" is a dynamic array. It's a pointer, to data and to some internal fields. "^array of byte" is a pointer to a pointer to data. You don't want this.

What you probably want is something like

type
    TByteArray = array[0..MaxInt - 1] of Byte;
    PByteArray = ^TByteArray;

Actually this should be already defined somewhere in the RTL (SysUtils unit, or maybe even in System) so you should just omit declaring PByteArray type yourself and all should be OK.

Michalis Kamburelis wrote

Koenraad Lelong wrote:

...

...
Thanks, that's the solution, it works now. Those types are defined in sysutils.
Regards,
Koenraad Lelong.