[R] allocating memory in a C module

[Rajarshi Guha]

Hi,
  I'm using a package that has a number of formats. I have C code to
parse these formats the results of which are generally integer arrays.

I would like to utilize these modules in R rather than writing R code to
read in these files (and also to learn about R extensions).

Essentially what I want is to do something like this:

load_tsets <- function(t,c,p)
.C( "c_load_tsets",
as.integer(t),
as.integer(c),
as.integer(p))

t,c,p should be R list objects, and empty when supplied to the function
load_tsets. On return each one will contain a list of integers. Thus in
the C function I need to allocate storage for the 3 arrays.

I've tried using Realloc but when I run the function the returned list
does not show an increase in length. I've included a simplified version
of the C code below:

#include<R.h>

void t(int *v)
{
    int i;
    v = (int*) Realloc(v,5,int*);
    for (i = 0; i < 5; i++)
        v[i] = i*i;
    printf("Hello\n");
    return;
}

I load it into R by doing:

> dyn.load('t.so')
> ft <- function(x)
+    .C('t',
+    as.integer(x))
>

Then I do

> x <- c()
> ret <- ft(x)
Hello
> ret 
[[1]]
numeric(0)

Do I need to go to the .Call interface? 

Is there any code that comes with the R distro (or if anybody has some
similar code that I could look at)?

Any pointers would be appreciated,
thanks,

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Rajarshi Guha <rxg218 at psu.edu> <http://jijo.cjb.net>
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