When using StreamReader to reader a file, the character that cannot be
converted to an encoding will be changed to a replace char ,like '?'.
Is there a way to know what the original char(bytes) is?

For example
My file has following lines
・　名詞相当語句：
・　ｔｈｉｎｋ　ｉｔ’ｓ　～　ｔｏ：
・名詞

the hex value:
EC 7D F6 BE 81 40 ......
EC 59 81 40......
81 45 .....

The original code for three '・'  are differenet.
EC7D , EC59 and 8145

But when using following code to read,
they are all changed to '・' (unicode: 0x30FB, shift-jis: 8145).

System.IO.StreamReader sr = new
System.IO.StreamReader(@"C:\test.txt",Encoding.GetEncoding("shift-jis"));
string line = sr.ReadLine();
line = sr.ReadLine();

Is there a way to know what is the original value for the '・' ?