GUID

globally unique identifier

128-bit

32 hexadecimal digit

ex:

BDA4A270-AIBA-lldO-BC2C-OOBOC73925BA

com interface & com implementation both have GUID

ex:

[object, uuid( BDA4A270-AIBA-lldO-BC2C-OOBOC73925BA)]

interface ITtest : IBaseInterface {

HRESULT add(void);

}

GUID structure in COM:

typedef struct _GUID {

DWORD Data1;

WORD Data2;

WORD Data3;

BYTE Data4[8];

} GUID;

typedef GUID IID; // GUID for interface

typedef GUID CLSID; // GUID for class implementation

CLSID: class id

IID: interface id

ex:

#include "wtypes.h"

// {FC3B3F61-BCEC-11D1-91FE-E1CBED988F66}

DEFINE_GUID(IID_IStack,

0xFC3B3F61, 0xBCEC, 0x11D1, 0x91, 0xFE,

0xE1, 0xCB, 0xED, 0x98, 0x8F, 0x66);

create new GUID:

1. use guidgen.exe

2. CoCreateGuid