[Rcpp-devel] Preferred idiom for obtaining a pointer in Rcpp
romain at r-enthusiasts.com
Tue Mar 16 08:43:52 CET 2010
Le 16/03/10 01:33, Douglas Bates a écrit :
> I have been using the begin method to obtain a pointer to the contents
> of an Rcpp::Vector object. For example
> Rcpp::NumericVector foo(10);
> double *ptr = foo.begin();
> Would a preferred idiom be
> double *ptr =&foo:
> In C I would use the REAL function to obtain a pointer to the contents
> of the R object.
Those three options are identical, although we cache the pointer so that
we don't have to call REAL each time, as we found this can be expensive.
I prefer begin, at least for readability (I have never really been
comfortable with the &).
You often see people using &v with std::vector because in that case
those are not identical, for example the gcc implementation of
vector::iterator is not a raw pointer so vector::begin() does not return
a pointer, but &x does.
Also, for not simple vectors (character, generic, expression), you
really have to go through with iterators because we cannot use pointers
here (write barrier).
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