[Rd] SEXP size management.

[Charles Danko]

Hi, Oleg,

Thanks very much for your answer!  I was indeed confused; thinking
that Realloc was intended to be an analog to realloc (except for SEXP
variables).

Is there a way to do either of the following:
-- resize the SEXP directly (for my purpose, I ONLY need to decrease
the size), or
-- assign it to to a C pointer that was allocated and used previously
in the function (and can thus be resized with realloc).

Thanks again,
Charles

On Wed, Mar 5, 2008 at 11:14 AM, Oleg Sklyar <osklyar at ebi.ac.uk> wrote:
> Rblah in your example is a SEXP structure. Realloc is an interface to C
>  realloc and is not intended to resize SEXP structures -- it is used to
>  resize user-controlled memory (which is generally not created by
>  allocVector/INTEGER).
>
>  You would expect a call like:
>
>  int * val;
>  ...
>  Realloc(val, 20, int);
>
>  Best,
>  Oleg
>
>
>
>  Charles Danko wrote:
>  > Hi,
>  >
>  > Trying to decrease the size of a SEXP variable without reassigning
>  > values individually in a loop.
>  >
>  > So far, I've tried using Realloc, as the follow source demonstrates:
>  > SEXP dothis() {
>  >       SEXP Rblah;
>  >       PROTECT(Rblah = NEW_INTEGER(6));
>  >
>  >       int* blah = INTEGER(Rblah);
>  >       blah[0] = 1;
>  >       blah[1] = 2;
>  >       blah[2] = 3;
>  >
>  >       Realloc(Rblah, 3, INTEGER);
>  >
>  >       UNPROTECT(1);
>  >       return(Rblah);
>  > }
>  >
>  > According to the documentation, I think that this should work, however
>  > it returns an error on compile: "test.c:17: error: expected expression
>  > before ')' token" (line 17 refers to the Realloc line).
>  >
>  > Another solution that will suit my needs is managing the variable in C
>  > and assigning the pointer to an R type in the end.  The following code
>  > gets at this, but int* and SEXP, INTEGER are incompatible:
>  > SEXP dothat() {
>  >       int* blah = malloc(3);// = INTEGER(Rblah);
>  >       blah[0] = 1;
>  >       blah[1] = 2;
>  >       blah[2] = 3;
>  >
>  >       SEXP Rblah;
>  >       PROTECT(Rblah = blah);
>  >
>  >       UNPROTECT(1);
>  >       return(Rblah);
>  > }
>  >
>  > Any suggestions for someone still new to SEXP memory management?
>  >
>  > Thanks,
>  > Charles
>  >
>  > ______________________________________________
>  > R-devel at r-project.org mailing list
>  > https://stat.ethz.ch/mailman/listinfo/r-devel
>
>  --
>  Dr Oleg Sklyar * EBI-EMBL, Cambridge CB10 1SD, UK * +44-1223-494466
>