[R] S_alloc or Calloc for return value

[David Winsemius]

On Jul 20, 2009, at 7:06 PM, Dan Kelley wrote:

>
> I am trying to write a C function to create a vector of integers  
> that can be
> used by the R calling function.  I do not know the size of the  
> vector in the
> R calling function.  (Well, actually, I have an upper limit on the  
> size, but
> that is so large that R cannot allocate it.  What I'm doing in the  
> function
> is to do a sieving procedure, and the result will be small enough to  
> fit
> into my machine's memory.)
>
> My reading of sections 6.1.1 and 6.1.2 of the guide on writing R  
> extensions
> has left me a bit confused.   Under R_alloc, I read "R will reclaim  
> the
> memory at the end of the call" which seems to suggest the storage  
> won't be
> made available afterwards, so that's not what I should use.  As for  
> the
> alterntaive, under Calloc, I read "This memory lasts until freed by  
> the
> user", and it's clear that this is to be done within the C function in
> question.
>
> Summary question: how can I allocate memory withing a C function,  
> making it
> available to an R function that calls the C function?
>
> Thanks.  Dan.
> --


You might look at the package bigmemory to see how they attacked the  
problem. In fact if my reading of their documentation is correct they  
may have already done your work for you:

http://www.stat.yale.edu/~jay/bigmemory

David Winsemius, MD
Heritage Laboratories
West Hartford, CT