[R] Limit on number of times Realloc can be called?

[Adam Waldemar Kowalewski]

Hello,

I've been writing a program in C that will be called by R. I seem to have
stumbled upon an odd error that seems to suggest there is a limit on the
number of times "Realloc" (the R version as defined in the manual
"R-extenstions" not the C version "realloc") when I try to use the
following program:

#include <R.h>
#include <Rinternals.h>

SEXP test_mem_alloc(SEXP z) {
	double *t = Calloc(sizeof(double), double);
	*t = 2;
	SEXP end_product;
	int i = 0;
	for(i=1; i < 20; i++) {
		t = Realloc(t, sizeof(t) + sizeof(double), double);
		t[i] = i;
	}
	PROTECT(end_product = allocVector(REALSXP,6));
	for(i = 0; i < 20; i++) {
		REAL(end_product)[i] = t[i];
	}
	UNPROTECT(1);
	Free(t);
	return end_product;
}

I call it from R using the following script:

z <- 1

test_mem_alloc <- function(z) {
	if(!(is.loaded("test_mem_alloc_v6"))) dyn.load("test_mem_alloc_v6.dll")
		out <- .Call("test_mem_alloc",
				as.double(z))
	return(out)
	dyn.unload("test_mem_alloc_v6.dll")
}

Basically I get the following error messages:

First:

"Runtime Error!

Program: C:\Program Files\R\R-2.10.0\bin\Rgui.exe

This application has requested the Runtime to terminate it in an unusual
way. Please contact the application's support team for more information."

The second error message is:

"The instruction at "0x0000002c". The memory could not be "read"."

Now, if change the number of times the program goes through the for loop
from 20 to say 6, and hence calls Realloc fewer times, then the program
runs without any problems. It does not seem to have anything to do with
the size of the memory being allocated as I changed the size of the total
memory being allocated with a "for" loop with only 6 iterations to
something that is substantially larger than the memory being allocated in
the "for" loop when calling Realloc twenty times and the program ran
successfully. Has anyone else come across this problem or knows about some
sort of limitation on using "Realloc" that is not specified in the R
documentation?

Any help would be greatly appreciated.

Yours sincerely

Adam Kowalewski