GUID (Microsoft COM UUID Mixed-Endian) constants in Clarion

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Some times I wondered why SV’s definition for GUIDs is structured as a group like this:

GUID                   group, type
Data1                     long
Data2                     short
Data3                     short
Data4                     byte, dim(8)
                       end

instead of something more straightforward, like guid STRING('<011h,022h,033h....>').

While troubleshooting a problem with an API call that expects a GUID constant, I found the answer in Wikipedia’s article on Universally unique identifier:

An exception to this are Microsoft’s variant 2 UUIDs (“GUID”): historically used in COM/OLE libraries, they use a little-endian format, but appear mixed-endian with the first three components of the UUID as little-endian and last two big-endian. Microsoft’s GUID structure defines the last eight bytes as an 8-byte array, which are serialized in ascending order, which makes the byte representation appear mixed-endian.[23] For example, 00112233-4455-6677-8899-aabbccddeeff is encoded as the bytes 33 22 11 00 55 44 77 66 88 99 aa bb cc dd ee ff .

Understanding this, a GUID constant can declared in the data section like this:

  PROGRAM

!00112233-4455-6677-8899-aabbccddeeff
GuidA               GROUP
Data1                 LONG(000112233h)
Data2                 SHORT(04455h)
Data3                 SHORT(06677h)
Data4Str              STRING('<088h,099h,0AAh,0BBh,0CCh,0DDh,0EEh,0FFh>') !There is no need for a byte array
                    END

!33 22 11 00 55 44 77 66 88 99 aa bb cc dd ee ff
Expected STRING('<033h,022h,011h,000h,055h,044h,077h,066h,088h,099h,0AAh,0BBh,0CCh,0DDh,0EEh,0FFh>')

  CODE
  PRAGMA('define(asserts=>on)')  
  
  ASSERT(GuidA = Expected)
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fyi, if you want to convert a GUID into a string, or vice versa, you can use UuidFromStringA & UuidToStringA from RPCRT4.DLL or CLSIDFromString & StringFromGUID2 from OLE32.DLL

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