C# 取得檔案名稱

 string filename = @"C:\Test\A.txt";

//取得檔名(不包含附檔名) --> A
var a = Path.GetFileNameWithoutExtension(filename);

//取得副檔名 --> .txt
var b = Path.GetExtension(filename);

//資料根目錄 --> C:\\
var c = Path.GetPathRoot(filename);

//取得檔案路徑 --> C:\\Test\\A.txt
var d = Path.GetFullPath(filename);

//取得資料夾路徑 --> C:\\Test
var e = Path.GetDirectoryName(filename);

//改變副檔名 --> C:\\Test\\A.doc
var f = Path.ChangeExtension(filename, "doc");