VB按字节截取字符串

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全角半角皆适用

    Public Function bSubstring(ByVal s As String, ByVal length As Integer) As String
        Dim bytes As Byte() = Text.Encoding.Unicode.GetBytes(s)
        

        Dim n As Integer = 0
       
    Dim i As Integer = 0
        
     While i < bytes.GetLength(0) AndAlso n < length

            If i And 1 = 0 Then
                n += 1
            Else
                If bytes(i) > 0 Then
                    n += 1
                End If
            End If
            i += 1
        End While

        If i Mod 2 = 1 Then
            If bytes(i) > 0 Then
                i = i - 1
            Else
                i = i + 1
            End If
        End If
        Return System.Text.Encoding.Unicode.GetString(bytes, 0, i)
    End Function