How can I extract data from Packed Record with external DLL using Delphi? -

i'm making delphi program using external dll. dll supports when request occurs sending window message client.

i defined packed record below:

type    // message packet send dll   trecv_packet = packed record     nid: integer;     lpdata: pointer;   end;   lprecv_packet = ^trecv_packet;    // request record   reqblock = packed record     id: array [0..7] of char   end;   lpreqblock = ^reqblock;    // response record   resblock = packed record     title: array[0..255] of char; _dt: char;     description: array[0..1204] of char; _time: char;   end;   lpresblock = ^resblock; 

if send request, dll send window message client. found out explanation in document. dll sends recv_packet's memory address in message.lparam. result, want datas of resblock using message.lparam. code wrote send broken datas always. want pure data it. how can do?

receiving message procedure below:

procedure tform.onreceivedata(var message: tmessage); var   recvpacket: lprecv_packet;   _resblock: lpresblock; begin   // actually, don't know why message.lparam parameter of lprecv_packet. how    recvpacket := lprecv_packet(message.lparam); works?    _resblock := lpresblock(recvpacket^.lpdata);    showmessage(_resblock^.title); // broken datas... end; 

updated:

the original api definition below:

function etk_request(hwnd: hwnd; psztrcode: pansichar; lpdata: pointer; ndatasize: integer; bnext: boolean; pszcontinuekey: pansichar; ntimeout: integer): integer; stdcall; external api_dll; procedure onreceivedata(var message: tmessage); message wm_user + xm_receive_data; 

we don't have documentation looking at. did find this online document (which not in english), this header file, , various online examples/translations vb, c#, , c++. based on those, delphi code should more this:

type   // message packet send dll   trecv_packet = packed record     nrqid: integer;     ndatalength: integer;     ntotaldatabuffersize: integer;     nelapsedtime: integer;     ndatamode: integer;     sztrcode: array[0..10] of ansichar;     ccont: array[0..0] of ansichar;     szcontkey: array[0..18] of ansichar;     szuserdata: array[0..30] of ansichar;     szblockname: array[0..16] of ansichar;     lpdata: pbyte;   end;   lprecv_packet = ^trecv_packet;    tmsg_packet = packed record     nrqid: integer;     nissystemerror: integer;     szmsgcode: array[0..5] of ansichar;     nmsglength: integer;     lpszmessagedata: pbyte;   end;   lpmsg_packet = ^tmsg_packet;    treal_recv_packet = packed record     sztrcode: array[0..3] of ansichar;     nkeylength: integer;     szkeydata: array[0..32] of ansichar;     szregkey: array[0..32] of ansichar;     ndatalength: integer;     pszdata: pansichar;   end;   lprecv_real_packet = ^trecv_real_packet;    // following records not documented or defined (where did them?),   // if above records indication, fields in these records   // should using ansichar fields...    // request record   reqblock = packed record     id: array [0..7] of ansichar;   end;   lpreqblock = ^reqblock;    // response record   resblock = packed record     title: array[0..255] of ansichar;     _dt: ansichar;     description: array[0..1204] of ansichar;     _time: ansichar;   end;   lpresblock = ^resblock;  ...  const   xm_disconnect = 1;   xm_receive_data = 3;   xm_receive_real_data = 4;   xm_login = 5;   xm_logout = 6;   xm_timeout_data = 7;  const   request_data = 1;   message_data = 2;   system_error_data = 3;   release_data = 4;  function etk_request(hparentwnd: hwnd; psztrcode: pansichar; lpdata: pointer; ndatasize: integer; bnext: bool; pszcontinuekey: pansichar; ntimeout: integer): integer; stdcall; external api_dll; procedure etk_releasemessagedata(lp: lparam); stdcall; external api_dll; procedure etk_releaserequestdata(nrequestid: integer); stdcall; external api_dll; 

type   tform1 = class(tform)   private     procedure onreceivedata(var message: tmessage); message wm_user + xm_receive_data;     ...   end;  procedure tform1.onreceivedata(var message: tmessage); var   recvpacket: lprecv_packet;   _resblock: lpresblock;   msgpacket: lpmsg_packet; begin   case message.wparam of     request_data: begin       recvpacket := lprecv_packet(message.lparam);       // make sure recvpacket^.ndatalength >= sizeof(resblock)       // before accessing data...       _resblock := lpresblock(recvpacket^.lpdata);       showmessage(_resblock^.title);     end;     message_data: begin       msgpacket := lpmsg_packet(message.lparam);       //...       etk_releasemessagedata(message.lparam);     end;     system_error_data: begin       msgpacket := lpmsg_packet(message.lparam);       //...       etk_releasemessagedata(message.lparam);     end;     release_data: begin       //...       etk_releaserequestdata(message.lparam);     end;   end; end;