Re: [Rd] external pointers

From: Prof Brian Ripley <>
Date: Mon 12 Dec 2005 - 08:16:55 GMT

On Mon, 12 Dec 2005, Roger Bivand wrote:

>> Where would be best to read about externalptr? I'm having trouble
>> finding material in the manuals or the site-search.
>> And would I need to use all the .Call machinery and C headers and SEXP
>> etc in order to handle externalptr objects?
> One package using externalptr is rgdal - Tim Keitt wrote the bindings to
> the external GDAL library for reading raster images to first return a
> pointer to a dataset (on disk) opened by GDAL, then to use the object to
> retrieve (parts of) the data. Most of the .Call/SEXP machinery is there
> (for the C++ case, GDAL is C++, so GDAL manages its own memory for its
> objects). The package also uses S4 classes, which may be overkill for your
> purposes.

RODBC is another, somewhat simpler, one.

There is documentation on, but my recollection is that is was not up to date (and in particular not re finalizers). On my TODO list is to add end-user documentation to `Writing R Extensions'.

Brian D. Ripley,        
Professor of Applied Statistics,
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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