Difference between -fileHandleForWritingAtPath: and fileHandleForUpdatingAtPath:?

For me it sounds like the same thing. Updating a file implies to write to the file. Writing to a file is also an update for me. But I guess 开发者_如何学Gothere's a subtle difference ;-)

Does anyone know?

---

fileHandleForWritingAtPath: returns an object that responds only to writeData:.

fileHandleForUpdatingAtPath: responds to both NSFileHandle read... messages and writeData:.