Interface identification: A GUID

An interface can be identified by a GUID. This is a 128-bit number, which is represented in a text representation (a string literal):

[’{HHHHHHHH-HHHH-HHHH-HHHH-HHHHHHHHHHHH}’]

Each H character represents a hexadecimal number (0–9, A–F). The format contains 8-4-4-4-12 numbers. A GUID can also be represented by the following record, defined in the objpas unit (included automatically when in DELPHI or OBJFPC mode):

PGuid = ^TGuid;
TGuid = packed record
   case integer of
      1 : (
           Data1 : DWord;
           Data2 : word;
           Data3 : word;
           Data4 : array[0..7] of byte;
          );
      2 : (
           D1 : DWord;
           D2 : word;
           D3 : word;
           D4 : array[0..7] of byte;
          );
      3 : ( { uuid fields according to RFC4122 }
           time_low : dword;
           time_mid : word;
           time_hi_and_version : word;
           clock_seq_hi_and_reserved : byte;
           clock_seq_low : byte;
           node : array[0..5] of byte;
           );
end;

{$mode objfpc}
program testuid;

Const
MyGUID : TGUID = ’{10101010-1010-0101-1001-110110110110}’;

begin
end.

Normally, the GUIDs are only used in Windows, when using COM interfaces. More on this in the next section.

7.2 Interface identification: A GUID