Le 01/07/10 14:24, Paul Theodor Pyl a écrit :
Hi all,
I have a question concerning the modification of R objects within C++
using Rcpp, what I would like to do is shown in this fantasy-R-session:
> l <- list()
> while( mycppfunc( l ) ){ print("running!") }
running!
running!
...
> l
$a
[1] "Something"
$b
...
The corresponding c++ function would look like this:
bool mycppfunc( List l ){
some_struct x;
if( some_other_function( x ) ){
l[x.name] = x.some_member;
return true;
}else{
return false;
}
}
where some_other_function is a c++ function that takes the struct and
modifies it returning a bool to indicate success/failure.
List::operator[] might move the memory around (if you add a new element
of the list), so the underlying SEXP will change. We have no choice
about this, this is dictated by the R API. You need to return the list
to the R level.
Something like:
while( TRUE ){
print("running!")
res <- mycppfunc( l )
if( ! res$more ) break ;
l <- res$l
}
And then internally return a list that contains both the actual result
and whether it needs to continue.
Alternatively, you could manage the loop internally in C++
Looking at the examples of Rcpp so far I have not found one where an R
object is handed to a c++ function that modifies it and returns a bool
to indicate success / failure.
How would I go about this? Could that be done using SEXP's (since they
are pointers I would suspect they can be modified 'in-place')
Adding an element to a list is achieved by essentially creating a new
list and copy the content of the initial list.
pairlists don't have that problem but they are weird animals on the R side.
Cheers,
Paul
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