var filePath = @"c:\doc\1.txt";
var dirPath1 = @"c:\music\";
var dirPath2 = @"c:\movie";

路径拼接

Console.WriteLine(Path.Combine(dirPath1, "a.mp3")); //c:\music\a.mp3
Console.WriteLine(Path.Combine(dirPath2, "b.mp4")); //c:\movie\b.mp4

C# Path