Koenraad Lelong wrote:
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;
"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.
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.
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