{-----------------------------------------------------------------------------
 Unit Name: mydll
 Author:    sam
 Date:      15-Apr-2018
 Purpose:   example how to pass a byte array from a dll to a host-application.
 History:
-----------------------------------------------------------------------------}
library mydll;
 
uses
  System.SysUtils,
  System.Classes;
 
{$R *.res}
 
type
TByteArray= array of byte;
 
var
  gDllBuffer:TByteArray;
 
{-----------------------------------------------------------------------------
  Procedure: InitData
  Author:    sam
  Date:      15-Apr-2018
  Arguments: out BufferSize:integer
  Result:    boolean
  Description: this method prepares some data and writes them to the global
               variable <gDllBuffer>.
-----------------------------------------------------------------------------}
function InitData(out BufferSize:integer):boolean;stdcall;
var
i:integer;
_SomeExampleData:TByteArray;
_ExampleDataSize:integer;
begin
  result:=false;
  SetLength(gDllBuffer,0);
// prepare some data
  Randomize;
  _ExampleDataSize:=Random(10000);
  SetLength(_SomeExampleData,_ExampleDataSize);
  for i := 0 to _ExampleDataSize-1 do _SomeExampleData[i]:=97+(i mod 26); // fill some data into the example array
// move the prepared data into the dll-internal buffer and return the buffersize to the host application.
  BufferSize:=length(_SomeExampleData);
  SetLength(gDllBuffer,BufferSize);
  Move(PByteArray(_SomeExampleData)^,PByteArray(gDllBuffer)^,BufferSize);
  result:=true;
end;
 
{-----------------------------------------------------------------------------
  Procedure: GetData
  Author:    sam
  Date:      15-Apr-2018
  Arguments: Buffer:PByte
  Result:    boolean
  Description: with this method the host-app will get the data from the dll.
-----------------------------------------------------------------------------}
function GetData(Buffer:PByte):boolean;stdcall;
begin
  result:=false;
  if Buffer=nil then exit;
  Move(PByteArray(gDllBuffer)^,Buffer^,length(gDllBuffer));
  result:=true;
end;
 
exports
  InitData,
  GetData;
end.

unit Unit1;
 
interface
 
uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls;
 
type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
  public
  end;
 
var
  Form1: TForm1;
 
implementation
 
{$R *.dfm}
 
type
TByteArray=array of byte;
 
TInitData= function (out BufferSize:integer):boolean;stdcall;
TGetData= function (Buffer:PByte):boolean;stdcall;
 
var
_InitData:TInitData;
_GetData:TGetData;
 
function GetDataFromDll(out Data:TByteArray):boolean;
var
_DllHandle:THandle;
_BufferSize:integer;
_Data:TByteArray;
begin
  result:=false;
  _DllHandle:=LoadLibrary('mydll.dll');
  if _DllHandle=0 then begin
    Showmessage('Problem to load dll <mydll.dll>.');
    exit;
  end;
  try
    _InitData:=getprocaddress(_DllHandle,'InitData');
    _GetData:=getprocaddress(_DllHandle,'GetData');
    if not _InitData(_BufferSize) then exit;           // this prepares some data in the dll and retunrs the buffer-size
    SetLength(_Data,_BufferSize);     // let's allocate the memoryspace
    if not _GetData(PByte(_Data)) then exit;      // and get the data from the dll.
    Data:=_Data;
    result:=true;
  finally
    FreeLibrary(_DllHandle);
    _DllHandle:=0;
  end;
end;
 
procedure TForm1.Button1Click(Sender: TObject);
var
_ByteData:TByteArray;
_AnsiString:AnsiString;
_String:String;
begin
  if not GetDataFromDll(_ByteData) then exit;
  _AnsiString:=TEncoding.ANSI.GetString(_ByteData);
  ShowmessageFmt('size: <%d>,data: <%s>',[length(_AnsiString),_AnsiString]);     // do whatever you want to do with the data. (in this example we build ANSI-string)  
  _String    :=TEncoding.UNICODE.GetString(_ByteData);  
  ShowmessageFmt('size: <%d>,data: <%s>',[length(_String),_String]);             // do whatever you want to do with the data. (in this example we build UNICODE-string)
end;
 
end.