bug or correct behaviour ?

 Dr. Ripley,

 Thanks for your answer, I guest the key is that
 in my code R can't know tmp is being modified.
 
 I couldn't find a duplicate function for the
 R environment. Is there any ?

 So I could avoid doing tmp.last <-tmp*1.0
  
 Thanks

 Alex
 


--- Prof Brian Ripley <ripley@stats.ox.ac.uk> wrote:

Without seeing your code for the .Call parts it is
impossible for us to
know, but as .Call does not duplicate its arguments
(unlike .C), it is
possible for it to change both tmp and a copy of
tmp, tmp.last.

So it seems likely there is a bug in your C code if
that is not your 
intention.  The normal way to use .Call is to return
something, and to 
duplicate any arguments which will be changed
(possibly only provided 
NAMED(tmp) is true as otherwise there are no named
copies around).

In other words, it would be normal to have

tmp <- .Call("Replace", tmp, ...)

and call duplicate() inside the C code for Replace.

On Thu, 10 Jun 2004, Alex Nu wrote:

 This is the general outline of my code::
 
main(argc,argv){
   ...
   Rf_initEmbeddedR(argc,argv);
   ...
   Test_tryEval("source(test.r)");
   ...
}

Not sure of the relevance of this.

############# 
# test.r
#############
...
dyn.load("toload.so")

tmp <-matrix(data=1,nrow=narray*2,ncol=nclust)

.Call("Init",tmp,...)
while(...) {
   criteria <-feval(tmp)
   if (criteria < criteria.min) 
        tmp.last <- tmp

That makes a potential copy. The actual copying
occurs if tmp is changed
and R is aware of it.  This is the purpose of the
'named' element of a
SEXP, but I don't think that is documented anywhere.

   else  
       tmp <- tmp.last
   ...
   .Call("replace",tmp,...)
}
####################################


 When I try to recover tmp 

      tmp <- tmp.last
 
 I got the modified value of tmp.
 It means that tmp.last is modified
 when I modified tmp in the C funciont replace.
 
 The program seems to work fine if I change 
 to this::
            
  tmp.last <- tmp*1.0
  
  tmp <- tmp.last*1.0

Those do definitely make new objects.

-- 
Brian D. Ripley,                 
ripley@stats.ox.ac.uk
Professor of Applied Statistics, 
http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865
272861 (self)
1 South Parks Road,                     +44 1865
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Oxford OX1 3TG, UK                Fax:  +44 1865
272595