\name{exportAttribute}
\alias{exportAttribute}

\title{Rcpp::export Attribute}

\description{
The \code{Rcpp::export} attribute is added to a C++ function definition to indicate that it should be made available as an R function. The \code{\link{sourceCpp}} and \code{\link{compileAttributes}} functions process the \code{Rcpp::export} attribute by generating the code required to call the C++ function from R.
}

\arguments{
  \item{name}{
    Specify an alternate name for the generated R function (optional, defaults to the name of the C++ function if not specified).
}
}

\details{
    Functions marked with the \code{Rcpp::export} attribute must meet several conditions to be correctly handled:
\enumerate{
    \item Be defined in the global namespace (i.e. not within a C++ \code{namespace} declaration).
    \item Have a return type that is either void or compatible with \code{Rcpp::wrap} and parameter types that are compatible with \code{Rcpp::as} (see sections 3.1 and 3.2 of the \emph{Rcpp-introduction} vignette for more details).
    \item Use fully qualified type names for the return value and all parameters. However, Rcpp types may appear without the namespace qualifier (i.e. \code{DataFrame} is okay as a type name but \code{std::string} must be specified fully).
}
    If default argument values are provided in the C++ function definition then these defaults are also used for the exported R function. For example, the following C++ function:
    
\preformatted{
DataFrame readData(
    CharacterVector file, 
    CharacterVector exclude = CharacterVector::create(),
    bool fill = true)
}

    Will be exported to R as:

\preformatted{
function (file, exclude = character(0), fill = TRUE)
}

    Note that C++ rules for default arguments still apply: they must occur consecutively at the end of the function signature and unlike R can't rely on the values of other arguments.

}

\note{
    When a C++ function has export bindings automatically generated by the \code{\link{compileAttributes}} function, it can optionally also have a direct C++ interface generated using the \code{\link[=interfacesAttribute]{Rcpp::interfaces}} attribute.
    
    The \code{Rcpp::export} attribute is specified using a syntax compatible with the new \href{http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2761.pdf}{generalized attributes} feature of the C++11 standard. Note however that since this feature is not yet broadly supported by compilers it needs to be specified within a comment (see examples below).
}

\seealso{
\code{\link{sourceCpp}} and \code{\link{compileAttributes}}
}

\examples{
\dontrun{

#include <Rcpp.h>

using namespace Rcpp;

// [[Rcpp::export]]
int fibonacci(const int x) {

   if (x == 0) return(0);
   if (x == 1) return(1);
   
   return (fibonacci(x - 1)) + fibonacci(x - 2);
}

// [[Rcpp::export("convolveCpp")]]
NumericVector convolve(NumericVector a, NumericVector b) {

   int na = a.size(), nb = b.size();
   int nab = na + nb - 1;
   NumericVector xab(nab);
    
   for (int i = 0; i < na; i++)
      for (int j = 0; j < nb; j++)
         xab[i + j] += a[i] * b[j];
    
   return xab;
}
}
}
