[Rcpp-devel] Accessing T of RcppVector<T>

Dirk's code relates to a question I meant to ask the experts for a while:
what's a safe and generic way to print C/C++ objects in an R session?

The background: forwarding the cout-stream in Dirk's example to R as below
doesn't work in the R-GUI on Windows (or in an IDE such as Eclipse); but it
does work if one runs an R session from the command line (that is, within
the console -- no surprise that the stream is correctly forwarded).

Additionally, there's a (confusing) variety of other print-functions that
successfully bridge the gap between C functions and the R-GUI, mostly made
available through prtutil.h. For instance, Rf_PrintValue takes an SEXP and
prints it to R using the "right format" when used in any C/C++-function,
whereas functions such as Rf_printIntegerVector  take C arguments (and
somehow smuggle them into the R session). And then there's the workhorse
Rprintf (which is possibly called by Rf_printIntegerVector).

Apologies for being so vague -- I would say I am eventually looking for a
way to make the below example run in the R-GUI, both to avoid using the
abovementioned functions, and to use existing C++-code that contains
summary/debugging overloads of cout. (This may belong to Rd and not to
Rcpp-devel, but I'm not sure.)

Best, Jo



2010/10/28 Dirk Eddelbuettel <edd at debian.org>

First, I (re-)define your helper function, making the argument const:

## define our helper function, this will be passed as an include segment

to cxxfunction()

inc <- 'void other(const double any) {

+            std::cout << "YAY it works, value is " << any << std::endl;
+         }
+        '

And use it:

num <- 42.1337
fun(num)

YAY it works, value is 42.1337
YAY it works, value is 42.1337
[1] 0

fun(3.1415)

YAY it works, value is 3.1415
YAY it works, value is 3.1415
[1] 0

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