Return values obviously, with suitably designed method contracts. Some (maybe most) types of I/O errors are proper exceptions. Parsing failures are not.
So now you have two different error paths, one in which the file can't be accessed, and one in which the file can be accessed but the contents are corrupted? The developer must handle exceptions and they must still check if the function returned some sentinel error value?
What's the point of forcing two different error paths on the developer?
They are different classes of errors, so you want different error paths. Parsing errors are common and should be handled locally with all of the usual logic. Exceptions are not supposed to be common errors which is why they trigger non-local control flow.
