string path = "C:\\dir1\\dir2\\foo.txt";

 string str = "GetFullPath：" + Path.GetFullPath(path) + "\r\n";

 str += "GetDirectoryName：" + Path.GetDirectoryName(path) + "\r\n";

 str += "GetFileName：" + Path.GetFileName(path) + "\r\n";

 str += "GetFileNameWithoutExtension：" + Path.GetFileNameWithoutExtension(path) + "\r\n";

 str += "GetExtension：" + Path.GetExtension(path) + "\r\n";

 str += "GetPathRoot：" + Path.GetPathRoot(path) + "\r\n";

 MessageBox.Show(str); 

结果： 

GetFullPath：C:\dir1\dir2\foo.txt

 GetDirectoryName：C:\dir1\dir2

 GetFileName：foo.txt

 GetFileNameWithoutExtension：foo

 GetExtension：.txt

 GetPathRoot：C:\