[R] observed power

Richards, Tom richards at pci.upmc.edu
Mon Jan 29 08:35:09 CET 2001


Here is my current version info:

platform i386-pc-mingw32
arch     x86            
os       Win32          
system   x86, Win32     
major    1              
minor    2.1            
year     2001           
month    01             
day      15             
language R              

I am using NT 4.0.  Modifying some C code I originally did under R version
1.1.1, I find in the R Extensions manual (p. 34), that I need to change


I am using VC++ 6.0, and I simply cannot get that change to work.  I am
going to just give a simple example which shows what is happening.  This
example uses the getAttrib() and getListElement() functions which appear in
many source files.  It works perfectly on 1.1.1, but gives an unread memory
error under 1.2.0.  Am I doing something wrong here?

First, a revised getListElement function, as suggested in the manual:

static SEXP getListElement(SEXP list, char *str)
	SEXP elmt = R_NilValue;
	SEXP names = getAttrib(list, R_NamesSymbol);
	int i;
	for (i = 0; i < length(list); i++)
#if R_VERSION < R_Version(1, 2, 0)
		if (strcmp(CHAR(STRING(names)[i]), str) == 0)
			elmt = VECTOR(list)[i];
	if (strcmp(CHAR(STRING_ELT(names,i)), str) == 0)
		elmt = VECTOR_ELT(list,i);
	return elmt;

Now, a simple calling function, called foo(), for Windows:

__declspec (dllexport) SEXP foo(SEXP input)
	SEXP L,V,tmp;

	input = CDR(input);L = CAR(input);
	input = CDR(input);V = CAR(input);

	tmp = getListElement(L, "b");
	return tmp;

I want to feed foo() a list and vector in R, so I made the R function

foo <- function(L,V){res <- .External("foo",L,V);res}

and I called

> foo(list(a=4,b=6),c(2,4,9))

This command yields 6, as it should, in version 1.1.1, but crashes version
1.2.1, with a "memory not read".

If you're still reading at this point, please note that I placed the two C
functions in a source file, and at the top I included:

#define VC

#include <math.h>
#include <R.h>
#include "Defn.h"
#include <Rdefines.h>

Is there something obvious here that I'm missing?  thanks in advance.

Tom Richards
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