Создаём собственный UnRar, используя unrar.dll

// Объявления

function RAROpenArchive(ArchiveData : Pointer): Integer; stdcall;
external 'unrar.dll' name 'RAROpenArchive';

function RARCloseArchive(hArcData : Integer): Integer; stdcall;
external 'unrar.dll' name 'RARCloseArchive';

function RARReadHeader(hArcData : Integer; HeaderData : Pointer):
Integer; stdcall;
external 'unrar.dll' name 'RARReadHeader';

function RARProcessFile(hArcData : Integer; Operation : Integer;
DestPath : Pointer; DestName : Pointer): Integer; stdcall;
external 'unrar.dll' name 'RARProcessFile';


const
  ERAR_END_ARCHIVE = 10;
  ERAR_NO_MEMORY = 11;
  ERAR_BAD_DATA = 12;
  ERAR_BAD_ARCHIVE = 13;
  ERAR_UNKNOWN_FORMAT = 14;
  ERAR_EOPEN = 15;
  ERAR_ECREATE = 16;
  ERAR_ECLOSE = 17;
  ERAR_EREAD = 18;
  ERAR_EWRITE = 19;
  ERAR_SMALL_BUF = 20;

  RAR_OM_LIST = 0;
  RAR_OM_EXTRACT = 1;
  RAR_SKIP = 0;
  RAR_TEST = 1;
  RAR_EXTRACT = 2;
  RAR_VOL_ASK = 0;
  RAR_VOL_NOTIFY = 1;

type
  Char260 = array [1..260] of Char;

  TRAROpenArchiveData = record
    ArcName : PChar; // в C++ это будет выглядеть как: char *ArcName
    OpenMode : Cardinal;
    OpenResult : Cardinal;
    CmtBuf : PChar;
    CmtBufSize : Cardinal;
    CmtSize : Cardinal;
    CmtState : Cardinal;
  end;

  TRARHeaderData = record
    ArcName : Char260;
    FileName : Char260;
    Flags : Cardinal;
    PackSize : Cardinal;
    UnpSize : Cardinal;
    HostOS : Cardinal;
    FileCRC : Cardinal;
    FileTime : Cardinal;
    UnpVer : Cardinal;
    Method : Cardinal;
    FileAttr : Cardinal;
    CmtBuf : PChar;
    CmtBufSize : Cardinal;
    CmtSize : Cardinal;
    CmtState : Cardinal;
  end;


var
  RARExtract : boolean;
  RAROpenArchiveData : TRAROpenArchiveData;
  RARComment : array [1..256] of Char;
  RARHeaderData : TRARHeaderData;

...

procedure ExtractRARArchive;
var
  sDir : string;
  s : string;
  sTest : string;
  iTest : integer;
  bTestDone : boolean;
  RARhnd : Integer;
  RARrc : Integer;
  PDestPath : Char260;
begin
  RARExtract:=TRUE;
  lKBWritten:=0;
  ProgressBar2.Position := 0;
  ProgressBar2.Max := lTotalSize;
  RARStartTime:=Time;

  RAROpenArchiveData.OpenResult:=99;
  RAROpenArchiveData.OpenMode := RAR_OM_EXTRACT; // открываем для распаковки
  RAROpenArchiveData.ArcName:= @RARFileName;
  RAROpenArchiveData.CmtBuf := @RARComment;
  RAROpenArchiveData.CmtBufSize := 255;

  // Открываем RAR архив и выделяем память
  RARhnd := RAROpenArchive (@RAROpenArchiveData);
  if RAROpenArchiveData.OpenResult <> 0 then
  begin
    case RAROpenArchiveData.OpenResult of
      ERAR_NO_MEMORY   : s:='Not enough memory to initialize data structures';
      ERAR_BAD_DATA    : s:='Archive header broken';
      ERAR_BAD_ARCHIVE : s:='File is not valid RAR archive';
      ERAR_EOPEN       : s:='File open error';
    end;
    MessageDlg('Unable to open rar archive: ' + s + '!',mtError, [mbOK], 0);
  end;

  RARSetProcessDataProc(RARhnd,@Form.OnRarStatus);
  StrPCopy(@PDestPath, EInstallPath.Text);

  repeat
    RARrc := RARReadHeader (RARhnd, @RARHeaderData);// Читаем заголовок
    if RARrc <> ERAR_END_ARCHIVE then
    begin
      ProgressBar1.Position := 0;
      ProgressBar1.Max := RARHeaderData.UnpSize;
      s:=RARHeaderData.FileName;
      lblCurrentFile.Caption := s;
      lKBytesDone := 0;
    end;

    if RARrc = 0 then
      RARrc:=RARProcessFile (RARhnd, RAR_EXTRACT, @PDestPath, nil);
    if (RARrc <> 0) and (RARrc <> ERAR_END_ARCHIVE) then
    begin
      MessageDlg('An Error occured during extracting of ' + sTest+'!' + #13#10 +
      'RARProcessFile: ' + MakeItAString(RARrc),mtError, [mbOK], 0);
    end;
  until
    RARrc <> 0;

  // закрываем RAR архив и освобождаем память
  if RARCloseArchive(RARhnd) <> 0 then
  begin
    MessageDlg('Unable to close rar archive!',mtError, [mbOK], 0);
  end;
end;