From: agemoagemo@...
Date: 2003-10-31T02:57:13+09:00
Subject: Re: Problem with seeking in existing files.


--- Warren Brown <wkb@airmail.net> wrote:
> Morgan,
> 
> > I'm trying to write a program that will be writing
> > data to an existing file, that will not
> necessarily
> > be done in the physical file order. I used mode
> > 'ab+' to open the file, as only the 'a' modes
> allow
> > writing without changing the existing file.
> 
>     It sounds like what you really want is to open
> the file with a mode
> of 'r+b'.  This allows reading and writing of the
> file without
> truncating the file (like 'w+b').  As you mentioned,
> a mode of 'ab'
> opens the file for writing only (at end of file). 
> To open for reading
> and writing (at end of file) you would need a mode
> of 'a+b'.  I believe
> a mode of 'ab+' is technically incorrect on most
> platforms, although it
> may work on some.

Well, I don't know about technical incorrectness, but
mode 'a+b' is identified as an illegal access mode,
wheras 'ab+' will execute.

Using mode 'rb+' seems to produce the behavior I
need... when the file exists. When it doesn't,
however, it produces:

in `initialize': No such file or directory - "new.zip"
(Errno::ENOENT)

Given the alternative, I'd be quite happy to work
around it by testing for the presence of a file, and
creating a new one if it doesn't exist... but I
haven't yet found a simple way to test for this.

-Morgan.

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