[Rcpp-devel] What is the "correct" way to print text to R with Rcpp?

[Jelmer Ypma]

Hi all,

another way is to define a new ostream as below. This is modified from
an answer on stackoverflow, where someone ran into a similar problem
with Matlab ( http://stackoverflow.com/questions/243696/correctly-over-loading-a-stringbuf-to-replace-cout-in-a-matlab-mex-file
). Using this code you can use something like in the regular way
Rcout << "test" << std::endl;

Hope this helps,
Jelmer

library('inline')
library('Rcpp')

include_code <- '
#include <streambuf>
#include <ostream>

#include <Rcpp.h>

// modified from
// http://stackoverflow.com/questions/243696/correctly-over-loading-a-stringbuf-to-replace-cout-in-a-matlab-mex-file

class Rstreambuf : public std::streambuf
{
	public:
	
	protected:
		virtual std::streamsize xsputn(
			const char *s,
			std::streamsize n );

		virtual int overflow(
			int c = EOF );
};

std::streamsize
Rstreambuf::xsputn(
	const char *s,
	std::streamsize num )
{
	Rprintf( "%.*s", num, s );
	return num;
}

int
Rstreambuf::overflow(
	int c )
{
    if (c != EOF) {
		Rprintf( "%.1s", &c );
    }
    return c;
}

class Rostream : public std::ostream
{
protected:
    Rstreambuf buf;

public:
    Rostream() : std::ostream( &buf ) {}
};

// declare global variable Rcout
Rostream Rcout;
'

example_class <- '
// Example class with two data members
// and overloaded operator<<
class Example
{
	friend std::ostream& operator<<(
		std::ostream& out,
		const Example& ex );

	private:
		double d_a;
		double d_b;
	
	public:
		Example(
			double _a,
			double _b )
				:
			d_a( _a ),
			d_b( _b )
		{};
};

std::ostream& operator<<(
	std::ostream& 	out,
	const Example& 	ex )
{
    out << "Example( " <<  ex.d_a << ", " << ex.d_b <<" )";
    return out;
}
'

src_code <- '
	Rcout << 1 << ", " << 2 << ", " << 3 << std::endl << "(" << 5 << ",
6)" << std::endl;
	
	double a = 1.234;
	int    b = 3;
	std::string s( "test" );
	Rcout << a << ", " << b << ", " << s << std::endl;

	Rcout << Example( 3.0, 4.0 ) << std::endl;
    return Rcpp::wrap<int>( 0 );
'

fun <- cxxfunction( signature(),
                    body = src_code,
                    includes = paste( include_code, example_class, sep='\n' ),
                    plugin="Rcpp",
                    verbose=TRUE )
fun()


On Tue, Oct 18, 2011 at 06:54, Tim Jurka <timjurka at gmail.com> wrote:
> Hi Slava,
>
> One way to do it is to use Rprintf() the same way you'd use the standard
> printf() command.
> Best,
> Tim
> On Oct 17, 2011, at 10:52 PM, Slava Razbash wrote:
>
> Hello,
>
> What is the "correct" way to print text to R with Rcpp? I find that
> "std::cout<<" will only work if i running R from a console. I am using
> winXP.
>
> Best Regards,
>
> Slava
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