Как записать правильно ReadFile

procedure TForm1.Button1Click(Sender: TObject);
var ZapisanoBytes : Cardinal;
    readpipe,writepipe: Thandle;
    Security: TSecurityAttributes;
    str:string;
    start: TStartUpInfo;
    ProcessInfo: TProcessInformation;
 
begin
 
with Security do
  begin
    nlength := SizeOf(TSecurityAttributes);
    binherithandle := true;
    lpsecuritydescriptor := nil;
  end;
if CreatePipe(readPipe,writepipe,@Security,0) then
 begin
    FillChar(Start, Sizeof(Start), #0);
    start.cb := SizeOf(start);
    start.hStdOutput := WritePipe;
    start.hStdInput := ReadPipe;
    start.dwFlags := STARTF_USESTDHANDLES +
    STARTF_USESHOWWINDOW;
    start.wShowWindow := SW_show;
 
 end;
 ShowMessage('da');
if CreateProcess(nil,
      'c:\cons.exe',
      @Security,
      @Security,
      true,
      NORMAL_PRIORITY_CLASS,
      nil,
      nil,
      start,
      ProcessInfo) then
    begin
 
      ShowMessage('da2');
      ReadFile(readpipe, str, Length(str), ZapisanoBytes, Nil);
      Memo1.Text:=str;
      CloseHandle(ProcessInfo.hProcess);
      CloseHandle(ProcessInfo.hThread);
      CloseHandle(ReadPipe);
      CloseHandle(WritePipe);
    end;
 
end;

ReadFile(readpipe, str, Length(str), ZapisanoBytes, Nil);