[Rd] .C returned array has odd results

From: Jonathan Lisic <jlisic_at_gmail.com>
Date: Fri, 27 Jan 2012 14:46:25 -0500


Hi, I'm sure this is a fairly simple problem, but I can't seem to find any specific information in the documentation as to what is going on. I am writing a simple nearest neighbor program that takes in a set of of points on a plane and returns the neighbors of those points, for a fixed number of neighbors. However, the returned integer array that is allocated in R seems to occasionally return incorrect results.

I thought this would be because of GC, but I thought this was only for SEXPs, or at least this is the impression I got from reading the documentation. So is there some obvious reason why my results seem to get mangled by this call? I have checked my program through several thousand loops in C, and always get the same results, so I assume that this is something I'm doing wrong in R.

Here is the code for my .C call. I could post the C code if someone thinks it's important, but I'm just changing the values of integer array specified in R.

r.result <-
.C("evalPoly",

 as.double(c.polygonX),
 as.double(c.polygonY),
 as.double(c.neighborX),
 as.double(c.neighborY),

 integer(c.numberOfNeighbors*c.height*c.length),
 as.integer(c.polygonLength),
 as.integer(c.neighborLength),
 as.integer(c.numberOfNeighbors),
 as.integer(c.length),
 as.integer(c.height),

 DUP=TRUE
)[[5]]

Cheers,

Jonathan

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