VB6: How To Convert UTF-8 Byte Arrays into Unicode Strings (and vice versa)

This code sample shows how to convert UTF-8 byte sequences (aka code page 65001) into unicode strings and back again in Visual Basic 6 instead of .Net like most of the examples I could find. What's more, this sample does not use APIs, but instead, relies on the Stream object provided by the ADODB library. This may not be the most efficient way of doing it, but these functions can be easily ported to Classic ASP by dropping all the variable types. For this code to work, you will need to add a reference to the Microsoft ActiveX Data Objects 2.5 Library later versions of this library will also work. The first function converts a unicode string to a byte array:

' accept a byte array containing utf-8 data
' and convert it to a string
Public Function ConvertStringToUtf8Bytes(ByRef strText As String) As Byte()

    Dim objStream As ADODB.Stream
    Dim data() As Byte
    
    ' init stream
    Set objStream = New ADODB.Stream
    objStream.Charset = "utf-8"
    objStream.Mode = adModeReadWrite
    objStream.Type = adTypeText
    objStream.Open
    
    ' write bytes into stream
    objStream.WriteText strText
    objStream.Flush
    
    ' rewind stream and read text
    objStream.Position = 0
    objStream.Type = adTypeBinary
    objStream.Read 3 ' skip first 3 bytes as this is the utf-8 marker
    data = objStream.Read()
    
    ' close up and return
    objStream.Close
    ConvertStringToUtf8Bytes = data

End Function

' accept a byte array containing utf-8 data
' and convert it to a string
Public Function ConvertUtf8BytesToString(ByRef data() As Byte) As String

    Dim objStream As ADODB.Stream
    Dim strTmp As String
    
    ' init stream
    Set objStream = New ADODB.Stream
    objStream.Charset = "utf-8"
    objStream.Mode = adModeReadWrite
    objStream.Type = adTypeBinary
    objStream.Open
    
    ' write bytes into stream
    objStream.Write data
    objStream.Flush
    
    ' rewind stream and read text
    objStream.Position = 0
    objStream.Type = adTypeText
    strTmp = objStream.ReadText
    
    ' close up and return
    objStream.Close
    ConvertUtf8BytesToString = strTmp

End Function

Public Sub Main()

    Dim strB64 As String
    Dim data() As Byte
    Dim strTmp As String
    
    ' define test data as base64 and decode to array of bytes
    strB64 = "R3JlZXRpbmdzIGFuZCBTYWx1dGF0aW9uISAo4oKsKSBhbmQgc29"
    strB64 = strB64 & "tZSBVcmR1OiDaqdix2KfahtuMINm+2Kfaqdiz2KrYp9mG24w="
    data = DecodeBase64(strB64)

    ' convert from utf-8 to string
    strTmp = ConvertUtf8BytesToString(data)
    
    ' convert back to bytes
    data = ConvertStringToUtf8Bytes(strTmp)
   
End Sub