Re: NSFileHandle or a better way?
Re: NSFileHandle or a better way?
- Subject: Re: NSFileHandle or a better way?
- From: Andrew Farmer <email@hidden>
- Date: Fri, 30 Jan 2009 16:14:52 -0800
On 30 Jan 09, at 06:44, Jaime Magiera wrote:
I've been using NSFIleHandle for a project that inserts data into a
file and synchs it back to disk. ... My apps ends up taking almost a
minute to perform all of its functions on a file of 500 megs.
Perhaps my overall approach was wrong to start out. What I've been
doing is opening a file handle, copying the data after the insertion
point to an NSData, truncating the file handle at the insertion
point, adding the new data, then adding back the trimmed data. This
works fairly well if the insert point is towards the end of the
file. However, there are instances where I need to insert a few
hundred kb into a the file at a location only a few hundred kb into
the file.
xxx ^ xxxxxxxxxxxxxxxxx
The time hit comes from copying the trim data to the NSData. Is
there a better way to do this with NSFileHandle? Is there a better
way to do this than NSFileHandle?
Not without changing the structure of your file. There's no way to
"shift" the contents of a file in the way you're looking for - UNIX
file systems aren't structured in a way that permits that. (In fact,
I'm not aware of any that are.) You'll need to either rethink how
you're storing data, or cope with slow saves.
Incidentally, the way you're doing saving is unsafe. If your
application crashes in the middle of a save operation, the file may
end up truncated.
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