Converting GUIDs to Strings
Windows only

by Dale Fugier (Last updated:  Wednesday, December 5, 2018)

Problem

If you have written a RhinoScript function which calls a method on a COM object that return an array of bytes with a GUID, you will likely want to convert this GUID into a string. Converting GUIDs to strings is possible, but it takes a little work.

Solution

The logical format of a GUID in memory is not in the same order as the bytes are in the string. A GUID stored in binary format in memory is a sixteen byte structure in the following format:

DWORD-WORD-WORD-BYTE BYTE-BYTE BYTE BYTE BYTE BYTE BYTE

Where a WORD consists of two bytes and a DWORD consists of four bytes. They are stored in memory in order from the least to the most significant, or “little endian”, on Intel-based systems. So, you need to make sure you decode the array in the correct order

The following example RhinoScript code demonstrates how to convert an array of bytes containing a GUID to a string.

' Returns single digit bytes, like 0, as "00", not "0"
Function HexByte(b)
  HexByte = Right("0" & Hex(b), 2)
End Function
 
' Converts a GUID to a string
Function GuidToString(ByteArray)
  Dim Binary, S
  Binary = CStr(ByteArray)
  ' Uncomment if you want opening paren
  ' S = "{"
  S = S & HexByte(AscB(MidB(Binary, 4, 1)))
  S = S & HexByte(AscB(MidB(Binary, 3, 1)))
  S = S & HexByte(AscB(MidB(Binary, 2, 1)))
  S = S & HexByte(AscB(MidB(Binary, 1, 1)))
  S = S & "-"  
  S = S & HexByte(AscB(MidB(Binary, 6, 1)))
  S = S & HexByte(AscB(MidB(Binary, 5, 1)))
  S = S & "-"  
  S = S & HexByte(AscB(MidB(Binary, 8, 1)))
  S = S & HexByte(AscB(MidB(Binary, 7, 1)))
  S = S & "-"  
  S = S & HexByte(AscB(MidB(Binary, 9, 1)))
  S = S & HexByte(AscB(MidB(Binary, 10, 1)))
  S = S & "-"  
  S = S & HexByte(AscB(MidB(Binary, 11, 1)))
  S = S & HexByte(AscB(MidB(Binary, 12, 1)))
  S = S & HexByte(AscB(MidB(Binary, 13, 1)))
  S = S & HexByte(AscB(MidB(Binary, 14, 1)))
  S = S & HexByte(AscB(MidB(Binary, 15, 1)))
  S = S & HexByte(AscB(MidB(Binary, 16, 1)))
  ' Uncomment if you want closing paren
  ' S = S & "}"
  GuidToString = S
End Function