VB.NETでSubstringB的な何か

Test.vb

' (参考) http://www.atmarkit.co.jp/bbs/phpBB/viewtopic.php?topic=20714&forum=7&start=8

Imports System
Imports System.Text

Class Test
	Public Shared Sub Main
		Dim t As New Test
		t.aaa()
	End Sub

	Public Sub aaa()
		Dim Rec As String = "@@@あ@@@い@@@う@うううう,@@@@@@@@@@@@@@@@@@@@@@@@@"
		'Dim SJIS As System.Text.Encoding = System.Text.Encoding.GetEncoding("Shift-Jis")
		'Dim RecB As Byte()=SJIS.GetBytes(Rec)
		Console.WriteLine(substringB(Rec, 0, 5))
		'Console.WriteLine(SJIS.GetString(RecB, 0, 5))
		Console.WriteLine(substringB(Rec, 5, 5))
		Console.WriteLine(substringB(Rec, 10, 5))
		Console.WriteLine(substringB(Rec, 15, 5))
		Console.WriteLine(substringB(Rec, 20, 5))
		Console.WriteLine(substringB(Rec, 25, 5))
		Console.WriteLine(substringB(Rec, 30, 5))
		Console.WriteLine(substringB(Rec, 35, 5))
		Console.WriteLine(substringB(Rec, 40, 5))
		Console.WriteLine(substringB(Rec, 45, 5))
	End Sub

	Private Function substringB(ByRef str As String, ByVal offset As Integer, ByVal bytes As Integer) As String
		Dim SJIS As System.Text.Encoding = System.Text.Encoding.GetEncoding("Shift-JIS")
		Dim RecB As Byte()=SJIS.GetBytes(str)
		Return SJIS.GetString(RecB, offset, bytes)
	End Function
End Class