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not safe to return vector pointer

2 messages · Chris Jeffery, Thomas Lumley

Original
Chris Jeffery
# 
Hello All,

I recently upgraded from R-1.1.1 to R-1.2.2.

I have an R function that uses .Call() to
return a list from C code.  The C code
has the form:

SEXP function(SEXP var)
{
   SEXP rlist ;  
   PROTECT(rlist = NEW_LIST(3)) ;  
   VECTOR_PTR(rlist)[0] = NEW_INTEGER(1) ;
   VECTOR_PTR(rlist)[1] = NEW_STRING(1) ;

   ...

   UNPROTECT(1) ;

   return(rlist) ;
}

When I try to .Call("function",...) from R I get
the following error message:

Error: not safe to return vector pointer

Why is it no longer safe to return a vector pointer?
How can I correct this problem?

Thanks in advance,

Chris
------------------------------------------------------------
Chris Jeffery  (cjeff at geog.ubc.ca)
Department of Geography,                 Tel: (604) 822-2663
University of British Columbia, B.C.     Fax: (604) 822-6150

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Thomas Lumley
#
On Mon, 10 Sep 2001, Chris Jeffery wrote:

            

      
      
      
    

        
If it was recent, it would have been better to update to R-1.3.0 or 1.3.1

            

      
      
      
    

        
The new memory manager in R 1.2 needs to know when objects are updated.
This means that there are new macros for access to strings and vectors.

You need to use eg

  SET_VECTOR_ELT(rlist,0,NEW_INTEGER(1));

instead of

  VECTOR(rlist)[0]=NEW_INTEGER(1));.

There are similar macros for string access.

More detail is given in the 'Writing R Extensions' manual. Modifying code
to handle this new `write barrier' isn't that painful and the new memory
manager is much better than the old one, so it was worth the change.


	-thomas

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