[Rcpp-devel] can one modify array in R memory from C++ without copying it?
edd at debian.org
Fri Nov 4 14:32:04 CET 2011
On 4 November 2011 at 08:28, romain at r-enthusiasts.com wrote:
| Not a bug, this is expected behaviour.
| If you pass a matrix of ints to the NumericVector ctor, Rcpp has no choice but to coerce the data to a matrix of double, which means new data, hence the original data does not get modified.
| If you pass a matrix of double, no copy is required, therefore Rcpp operates directly on the data.
| Those are features.
And they are documented.
| Le 4 nov. 2011 à 08:01, Darren Cook <darren at dcook.org> a écrit :
| >> I.e. the point of his code was to show that a matrix of doubles gets
| >> modified, a matrix of ints does not.
| > Or change the first line from NumericMatrix to:
| > Rcpp::IntegerMatrix r_m(mem);
| > Then the behaviour is reversed. The matrix of doubles does not get
| > modified, but the matrix of ints does!
| > Dirk, Romain, this is a bug-in-waiting. Is there any way to generate a
| > warning when the implicit deep copy happens? Or alternatively when the
| > pointer is being used implicitly... but my hunch is that I want to know
| > when there is any implicit conversion between int and double: modern C++
| > style is to explicitly declare all type conversions with static_cast<>
| > and friends.
| > Darren
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