how send data record using SendMessage(..) in separate process - delphi

Question

i use to send a data on two separate process but it fails. it works only under same process... this is concept.
//-----------------------------------------------------------------------------------
MainApps
//-----------------------------------------------------------------------------------
Type
PMyrec = ^TMyrec;
TMyrec = Record
name : string;
add : string;
age : integer;
end;
:OnButtonSend
var aData : PMyrec;
begin
new(aData);
aData.Name := 'MyName';
aData.Add := 'My Address';
aData.Age : 18;
SendMessage(FindWindow('SubApps'),WM_MyMessage,0,Integer(#aData));
end;
//-----------------------------------------------------------------------------------
SubApps
//-----------------------------------------------------------------------------------
Type
PMyrec = ^TMyrec;
TMyrec = Record
name : string;
add : string;
age : integer;
end;
:OnCaptureMessage
var
aData : PMyrec;
begin
aData := PMyrec(Msg.LParam);
showmessage(aData^.Name);
end;

Answer 1

You're right. Addresses only have meaning within a single process. The PMyRec value you create in the first process is just a garbage address in the target process.
To send an arbitrary block of memory to another process via a window message, you should use the wm_CopyData message. You give that message the address of the data and the size, and the OS takes care of copying it into the target process's address space.
Since your data includes a string, which is represented internally as a another pointer, it won't be enough to just copy the 12 bytes of your record. You'll need to allocate additional memory to hold the record and the string data in a single block of memory so wm_CopyData can copy it and the target process can read it.
Here's one way to do it, using a stream to collect the data into a single block of memory.
procedure SendRecord(Source, Target: HWnd; const Rec: TMyRec);
var
Buffer: TMemoryStream;
Len: Integer;
CopyData: TCopyDataStruct;
begin
Buffer := TMemoryStream.Create;
try
Len := Length(Rec.name);
Buffer.Write(Len, SizeOf(Len));
if Len > 0 then
Buffer.Write(Rec.name[1], Len * SizeOf(Char));
Len := Length(Rec.add);
Buffer.Write(Len, SizeOf(Len));
if Len > 0 then
Buffer.Write(Rec.add[1], Len * SizeOf(Char));
Buffer.Write(Rec.age, SizeOf(Rec.age));
CopyData.dwData := 0;
CopyData.cbData := Buffer.Size;
CopyData.lpData := Buffer.Memory;
SendMessage(Target, wm_CopyData, Source, LParam(#CopyData));
finally
Buffer.free;
end;
end;
We write the lengths of the strings in addition to the strings' characters so that the recipient knows how many characters belong to each one. The recipient's code will look like this:
procedure TBasicForm.WMCopyData(var Message: TWMCopyData);
var
Rec: TMyRec;
Len: Integer;
Buffer: TStream;
begin
Buffer := TReadOnlyMemoryStream.Create(
Message.CopyDataStruct.lpData, Message.CopyDataStruct.cbData);
try
if Message.CopyDataStruct.dwData = 0 then begin
Buffer.Read(Len, SizeOf(Len));
SetLength(Rec.name, Len);
if Len > 0 then
Buffer.Read(Rec.name[1], Len * SizeOf(Char));
Buffer.Read(Len, SizeOf(Len));
SetLength(Rec.add, Len);
if Len > 0 then
Buffer.Read(Rec.add[1], Len * SizeOf(Len));
Buffer.Read(Rec.age, SizeOf(Rec.age));
// TODO: Do stuff with Rec here.
Message.Result := 1;
end else
inherited;
finally
Buffer.Free;
end;
end;
I've used the non-standard TReadOnlyMemoryStream since it makes everything easier. Here's a simple implementation for it:
type
TReadOnlyMemoryStream = class(TCustomMemoryStream)
public
constructor Create(Mem: Pointer; Size: LongInt);
function Write(const Buffer; Count: LongInt): LongInt; override;
end;
constructor TReadOnlyMemoryStream.Create;
begin
inherited Create;
SetPointer(Mem, Size);
end;
function TReadOnlyMemoryStream.Write;
begin
Result := 0;
end;