Duncan,
extern "C" just means that the function(s) below it have C calling
conventions, so that .Call, .External, ... can find them. Without this,
your function names would be c++ mangled to disambiguate different
overloads.
What is inside can use namespace without any issue. You'd have something
like:
extern "C" SEXP dot_call_function(){
rgl::Whatever object(1, 2 ) ;
object.do_something() ;
return R_NilValue ;
}
IIRC, if you register your functions (see WRE #5.4), you don't need
those extern "C" because you directly give the function pointer so you
don't have to search for it with its name.
Romain
Le 02/10/13 19:45, Duncan Murdoch a écrit :
Thanks Dirk, Martyn and Romain. I'm planning to do a temporary
workaround release with the Shape class renamed to rglShape, but over
the longer term I'll put everything that's supposed to be local inside
an rgl namespace. First I need to learn how namespaces interact with
extern "C" declarations; pointers to any readable tutorials would be
appreciated.
Duncan Murdoch
On 02/10/2013 11:52 AM, Dirk Eddelbuettel wrote:
On 2 October 2013 at 15:45, Martyn Plummer wrote:
| In C++, everything goes in the global namespace unless the programmer
| explicitly creates one. So when you dynamically load two dynamic shared
| libraries with a "Shape" object they clash.
|
| The solution here is to put
|
| namespace rgl {
| ...
| }
|
| around your class definitions in the rglm package, and
|
| using rgl::Shape
Exactly.
| at the top of any source file that refers to rgl Shape. Likewise, the
| igraph package should declare shape in the "igraph" namespace.
And as I wrote to Duncan off-list, igraph doesn't, even though it
otherwise
uses an igraph namespace:
/** Shape.h
*/
#ifndef SHAPE_H
#define SHAPE_H
#include <string>
#include "Color.h"
#include "Ray.h"
#include "Point.h"
class Shape
[....]
So the clash is due to two packages simulatenously failing to make use of
namespaces.
And at that point the linker appears to pick in search (link ?) order.
Dirk
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
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