{ You maybe have to access just a part of a GUID. }

{ Const for the function Format(...) }
const
 fsGUID: string = 'D1: $%s'#13#10'D2: $%s'#13#10'D3: $%s'#13#10 +
  'D4: $%s $%s $%s $%s $%s $%s $%s $%s';
 fsGUIDParts: string = 'D%d:%s';
 // Type for the GUID part to be shown
type
 TGUIDPART = (guidp_NoFormat, guidp_All, guidp_D1,
  guidp_D2, guidp_D3, guidp_D4);
{ This GUIDToStringEx function give you the full GUID string
 according with then format string FStr (you can change it !!!) }
function GUIDToStringEx(Guid: TGuid; FStr: string): string; overload;
begin
 Result := Format(FStr,
  [IntToHex(GUID.D1, 8),
  IntToHex(GUID.D2, 4),
  IntToHex(GUID.D3, 4),
  IntToHex(GUID.D4[0], 2),
  IntToHex(GUID.D4[1], 2),
  IntToHex(GUID.D4[2], 2),
  IntToHex(GUID.D4[3], 2),
  IntToHex(GUID.D4[4], 2),
  IntToHex(GUID.D4[5], 2),
  IntToHex(GUID.D4[6], 2),
  IntToHex(GUID.D4[7], 2)
  ]);
end;
{ This GUIDToStringEx function give you the part of the GUID
 to be shown, according to the part type GUIDPart }
function GUIDToStringEx(Guid: TGuid; Part: TGUIDPART): string; overload;
var
 i: Integer;
 S: string;
begin
 S := '';
 case Part of
  guidp_NoFormat: S := GUIDToString(Guid);
  guidp_All: S := GUIDToStringEx(Guid, fsGUID);
  guidp_D1: S := Format(fsGUIDParts, [1, ' $' + IntToHex(GUID.D1, 8)]);
  guidp_D2: S := Format(fsGUIDParts, [2, ' $' + IntToHex(GUID.D2, 4)]);
  guidp_D3: S := Format(fsGUIDParts, [3, ' $' + IntToHex(GUID.D3, 4)]);
  guidp_D4:
  begin
  for i := 0 to 7 do S := S + ' $' + IntToHex(GUID.D4[i], 2);
  S := Format(fsGUIDParts, [4, S]);
  end;
  else
  S := '?';
 end;
 Result := S;
end;
{ How to use the different GUIDToStringEx functions }
procedure TForm1.Button1Click(Sender: TObject);
var
 NewGUID: TGUID;
begin
 { Create a new GUID }
 NewGUID := StringToGUID(CreateClassID);
 { Standard formated GUID string }
 label1.Caption := GUIDToStringEx(NewGUID, guidp_NoFormat) +
  #13#10 +
  { Full formated GUID string acc. with fsGUID}
  GUIDToStringEx(NewGUID, fsGUID) +
  #13#10 +
  { Full formated GUID string with default formating}
  GUIDToStringEx(NewGUID, guidp_All) +
  #13#10 +
  { Part D3 of the GUID only }
  GUIDToStringEx(NewGUID, guidp_D3);
end;