Creating+a+Globally+Unique+Identifier

//by Richard Russell, April 2007//

A **Globally Unique Identifier**, or **GUID** for short, is a 128-bit (16 byte) number which, as its name suggests, is intended to be unique in the world - or possibly in the universe! GUIDs are often represented in a textual form as follows:

code {A8A8D3E5-713D-4C00-897E-F3B225E3A3AF} code GUIDs are used for a number of purposes in Windows, most notably to identify a **COM interface** (IID) or **class** (CLSID); in those cases you must discover the correct value to use from Microsoft's documentation.

GUIDs are also useful whenever you need to identify something uniquely. For example in the article Detecting a second instance of a program it is suggested that a GUID be used as the **UniqueLockName**. In such cases it is up to you to create a GUID for the purpose.

There is no guarantee that a GUID is genuinely unique, but statistically the likelihood of any two being the same is small. Whilst you could simply make up your own 128-bit number 'at random' (whatever that means) it is far better to use one of the means provided specially for the purpose. One is the following website, which will create a new GUID on request: [].

An alternative method is to use your own program. The code below will generate a new GUID whenever you need one:

code format="bb4w" SYS "LoadLibrary", "OLE32.DLL" TO ole32% SYS "GetProcAddress", ole32%, "CoCreateGuid" TO CoCreateGuid% SYS "GetProcAddress", ole32%, "StringFromGUID2" TO StringFromGUID2% DIM guid{a%, b%, c%, d%}, guidw% 79, guida% 39 SYS CoCreateGuid%, guid{} SYS StringFromGUID2%, guid{}, guidw%, 40 SYS "WideCharToMultiByte", 0, 0, guidw%, -1, guida%, 40, 0, 0 PRINT $$guida% code The GUID is available as a 128-bit number in the structure **guid{}**, as a Unicode (16-bit) string at **guidw%** and as a NUL-terminated ANSI (8-bit) string at **guida%**.