R help - Dec 2002 - readLines() changes mode of connection

Hi,

It seems like reading a line from a gzfile() connection changes the mode of
the connection from text to binary (it also alters "can write", in
case it
matters). The following transcript, produced on RedHat 7.1, demonstrates
this "feature" (note the evolution of file$text). Is this expected?

Thanks, Vadim

> file <- gzfile("foo.gz")
file <- gzfile("foo.gz")
> summary(file)
summary(file)
$description
[1] "foo.gz"

$class
[1] "gzfile"

$mode
[1] "rb6"

$text
[1] "text"

$opened
[1] "closed"

$"can read"
[1] "yes"

$"can write"
[1] "yes"
> hdr <- readLines(file, 1)
hdr <- readLines(file, 1)
> summary(file)
summary(file)
$description
[1] "foo.gz"

$class
[1] "gzfile"

$mode
[1] "rb6"

$text
[1] "binary"

$opened
[1] "closed"

$"can read"
[1] "yes"

$"can write"
[1] "no"



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The `text' field is *not* the mode: look at your own output.

This is expected.  In your first output the connection has not been
opened.  You asked provisionally for a binary mode, but this is
provisional until the connection has actually been opened.
readLines does open the connection.

The fields of a connection are not documented.

On Sun, 1 Dec 2002, Vadim Ogranovich wrote:
> Hi,
>
> It seems like reading a line from a gzfile() connection changes the mode of
> the connection from text to binary (it also alters "can write",
in case it
> matters). The following transcript, produced on RedHat 7.1, demonstrates
> this "feature" (note the evolution of file$text). Is this
expected?
>
> Thanks, Vadim
>
>
> > file <- gzfile("foo.gz")
> file <- gzfile("foo.gz")
> > summary(file)
> summary(file)
> $description
> [1] "foo.gz"
>
> $class
> [1] "gzfile"
>
> $mode
> [1] "rb6"
>
> $text
> [1] "text"
>
> $opened
> [1] "closed"
>
> $"can read"
> [1] "yes"
>
> $"can write"
> [1] "yes"
>
> > hdr <- readLines(file, 1)
> hdr <- readLines(file, 1)
> > summary(file)
> summary(file)
> $description
> [1] "foo.gz"
>
> $class
> [1] "gzfile"
>
> $mode
> [1] "rb6"
>
> $text
> [1] "binary"
>
> $opened
> [1] "closed"
>
> $"can read"
> [1] "yes"
>
> $"can write"
> [1] "no"
>
>
>
> --------------------------------------------------
> DISCLAIMER
> This e-mail, and any attachments thereto, is intended only for use by the
> addressee(s) named herein and may contain legally privileged and/or
> confidential information.  If you are not the intended recipient of this
> e-mail, you are hereby notified that any dissemination, distribution or
> copying of this e-mail, and any attachments thereto, is strictly
prohibited.
> If you have received this e-mail in error, please immediately notify me and
> permanently delete the original and any copy of any e-mail and any printout
> thereof.
>
> E-mail transmission cannot be guaranteed to be secure or error-free.  The
> sender therefore does not accept liability for any errors or omissions in
> the contents of this message which arise as a result of e-mail
transmission.
>
> NOTICE regarding privacy and confidentiality
>
> Knight Trading Group may, at its discretion, monitor and review the content
> of all e-mail communications.
>
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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