A second example of using Boost

Dirk Eddelbuettel — written Jan 15, 2013 — source

We introduced Boost in a first post doing some integer math. In this post we want to look at the very versatile Boost.Lexical_Cast library to convert text to numbers – see the Motivation for more.

As before, I should note that I initially wrote this post on a machine with Boost in a standard system location. So stuff just works. Others may have had to install Boost from source, and into a non-standard location, which may have required an -I flag, not unlike how we initially added the C++11 flag in this post before the corresponding plugin was added.

This is now automated thanks to the BH package which, if installed, provides Boost headers for use by R in compilations just like this one.

// We can now use the BH package
// [[Rcpp::depends(BH)]]

#include <Rcpp.h>
#include <boost/lexical_cast.hpp>  	// one file, automatically found for me

using namespace Rcpp;

using boost::lexical_cast;
using boost::bad_lexical_cast;
// [[Rcpp::export]]
std::vector<double> lexicalCast(std::vector<std::string> v) {

    std::vector<double> res(v.size());

    for (unsigned int i=0; i<v.size(); i++) {
        try {
            res[i] = lexical_cast<double>(v[i]);
        } catch(bad_lexical_cast &) {
            res[i] = NA_REAL;

    return res;

This simple program uses the exceptions idiom we discussed to branch: when a value cannot be converted, a NA value is inserted.

We can test the example:

v <- c("1.23", ".4", "1000", "foo", "42", "pi/4")
[1]    1.23    0.40 1000.00      NA   42.00      NA

tags: basics  boost 

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