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 = 

     Dim i As Integer = 

      While i < bytes.GetLength() AndAlso n < length

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

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