Actually, there is a known issue: it is often wrong for binary files opened in append mode, and we have caught by that too. So those writers did make the sort of error I did not trust them not to make.
On Wed, 15 Jun 2005, Prof Brian Ripley wrote:
I think the proposed change is appropriate only if the return value is *known* to be reliable for binary files. I for one do not trust the writers of an OS whom have made such a serious error in one mode (and many other errors elsewhere) not to have made one in closely related code. Since it is not Open Source, we cannot find out. On Wed, 15 Jun 2005 tplate at blackmesacapital.com wrote:
[I started a new bug report for this issue because it was not the primary issue in the original discussion, which was PR#7899] ligges at statistik.uni-dortmund.de wrote:
Tony Plate wrote: [snip]
ligges at statistik.uni-dortmund.de wrote: [snip]
Note that ?seek currently tells us "The value returned by seek(where=NA) appears to be unreliable on Windows systems, at least for text files." It would be nice if this comment could be removed, of course ....
May the explanation could be given that this happens with text files because Windows inserts extra characters at end-of-lines when reading "text" mode files (but with binary files, things should be fine.) This particular issue is documented in Microsoft Windows documentation (e.g., at http://msdn2.microsoft.com/library/75yw9bf3(en-us,vs.80).aspx, found by searching on Google using the terms "fseek windows documentation"). Are there any known issues using seek with binary files under Windows? If there are not, then the caveat could be made specific to text files and all vagueness removed.
Hmm, all I find (including your link) is Windows CE related ... Uwe Ligges
For the record, the documentation I pointed to is for Windows 2000 etc,
and is not just related to Windows CE (Uwe retracted that claim in a
private email).
So, the suggestion to refine the note in ?seek stands. Perhaps
src/library/base/man/seek.Rd could be changed as follows:
OLD:
#ifdef windows
The value returned by \code{seek(where=NA)} appears to be unreliable
on Windows systems, at least for text files. Clipboard connections
can seek too.
#endif
NEW:
#ifdef windows
The value returned by \code{seek()} is unreliable
on Windows systems for text files. This is because the Windows
file-I/O functions can insert extra characters at end-of-lines
when working with text mode files. Binary mode files should not
be affected by this issue. Clipboard connections can seek too.
#endif
Of course, if someone knows that the return value of seek() is
unreliable on Windows for binary files, this documentation change is
innappropriate (and then the documentation should probably be changed
from "appears to be unreliable, at least for text files" to "is
unreliable, for both binary and text files".
-- Tony Plate
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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 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595
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 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595