Re: Why doesn't (open ... :if-exists) support :truncate?

David Lichteblau <usenet-2006@xxxxxxxxxxxxxx> writes:

SBCL's :APPEND has a similar bug. The spec says "The file pointer is
initially positioned at the end of the file", but SBCL maps it to
O_APPEND instead.

Well clearly the file pointer is supposed to be positioned to the end
of the file, but I don't see anything that says that says the
implementation is forbidden from opening the file with O_APPEND-y
semantics, only that the file is destructively modified.

(Also, if you're interested in being able to do random-access writes,
doing and starting at the end of the file, I would expect this to do
the trick on Unix file systems:

(with-open-file (stream pathname :direction :overwrite)
(file-position stream :end)
... stuff ...)

This might not work on some other file systems though. For example,
while the Unix file system ensures that when you lseek to or past the
end of a file and then do some writing, the file will automatically be
resized (possibly sparsely), I think I've read that some older file
systems required you to manually allocate space for files; anyway you
can imagine a file system like that. Maybe a CL implementation that
talked to such a file system would constrain :OVERWRITE to not resize
the file, but have :APPEND do the resizing implicitly.)

--
.

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