On 12 August 2011 at 16:59, Chris DuBois wrote:
| Point taken: STL looks like the way to go in general.
|
| In my particular example, however, the arrays get immediately cast to another
| structure foo (somebody else's code). So I need to cast from IntegerVector to
| int[] before they get cast to foo[]. What you suggested works perfectly (and
| makes sense in hindsight).
|
| Is the story identical for char[]? Where x is a CharacterVector, I tried
|
| char* a = x.begin();
|
| and got
| error: cannot convert ‘Rcpp::Vector<16>::iterator’ to ‘char*’ in
| assignment
char can be a pain. It is something C and C++ didn't get quite right by
lacking a base type for string. Doing it in plain C (as in *argv[] from
main()) is a pain but doable.
CharacterVector works as the equivalent of std::vector< std::string >. Out of
each element (ie string) you can extract the underlying char* but you may
have to rely on strcmp etc. Remember that you may be dealing with pointers
of pointers...
Have a peek at the unitTests/ directory to see if you find something.
Hope this helps, Dirk
| Any help much appreciated.
| Chris
|
| On Fri, Aug 12, 2011 at 3:19 PM, Dirk Eddelbuettel <e...@debian.org> wrote:
|
|
| On 12 August 2011 at 14:50, Chris DuBois wrote:
| | Hi all,
| |
| | I'm trying to figure out how to pass in an array of integers to a
| function
| | inside a module. For example, adding the following function to
| runit.Module.R
| | works fine:
| |
| | int bla3( IntegerVector x ) {
| | return sum(x);
| | }
| |
| | However, I need to pass an int array, rather than an IntegerVector.
| Using int
| | x[] in the arguments doesn't compile (though I'm unfamiliar with C++ in
| | general, so maybe this shouldn't work anyway).
| |
| | Alternatively, should I just cast x from an IntegerVector to an int
| array? I
| | tried various permutations of as, vector, <int>, etc, and would like to
| learn
| | the proper way of doing this.
|
| You generally do not want old school x[] arrays in C++. Why? Because STL
| vectors do _everything_ they do at (essentially) zero added cost, free you
| from malloc/free and still allow you to access the straight memory should
| you
| need to (to talk to a C API, say).
|
| So use IntegerVector for _the interface_. You can the, if you must, do
|
| IntegerVector x;
|
| int a1[] = x.begin(); // STL-style iterator to beginning of
| memory
| int *a2 = x.begin(); // idem
|
| Hope this helps, Dirk
|
| --
| Two new Rcpp master classes for R and C++ integration scheduled for
| New York (Sep 24) and San Francisco (Oct 8), more details are at
| http://dirk.eddelbuettel.com/blog/2011/08/04#
| rcpp_classes_2011-09_and_2011-10
| http://www.revolutionanalytics.com/products/training/public/
| rcpp-master-class.php
|
|
--
Two new Rcpp master classes for R and C++ integration scheduled for
New York (Sep 24) and San Francisco (Oct 8), more details are at
http://dirk.eddelbuettel.com/blog/2011/08/04#rcpp_classes_2011-09_and_2011-10
http://www.revolutionanalytics.com/products/training/public/rcpp-master-class.php
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