[Rcpp-devel] Understanding the behaviour of const CharacterVector as a function parameter

[Dirk Eddelbuettel]

On 29 September 2013 at 14:06, Simon Zehnder wrote:
| Dear Rcpp::Users and Rcpp::Devels,
| 
| I would like to understand a certain behaviour of my code I encountered lately. 
| 
| I am working with CharacterVector and the following behaviour occurred:
| 
| void test1 (Rcpp::CharacterVector &charv)
| {
| 	Rprintf("test1: %s\n", (char*) charv(0));
| }
| 
| void test2 (const Rcpp::CharacterVector &str)
| {
| 	Rprintf("test2: %s\n", (char*) charv(0));
| }
| 
| Using a string like "2013-05-04 20:23:21" for the Rcpp::CharacterVector gives the following outputs:
| 
| test1: 2013-05-04 20:23:21
| 
| test2:  `
| 
| This does also not change if I use a cast to const char* in test2. I tried something similar with strings and printing the c_str() of them, there the 'const' keyword does not make a difference - it always prints the correct string.
| 
| Is this something specific to the Rcpp::CharacterVector, that uses a string_proxy for its elements returned by the operator ()? Is there a way to use const Rcpp::CharacterVector and get the behaviour of test1? 

Looks like a bug. (But note that const correctness of types build around SEXP
is at best a promise -- we cannot undo the fact the the SEXP _is_ a pointer.)

But hold on for a day til Rcpp 0.10.5 reaches your mirror, or grab it from
CRAN in Vienna. It brings a lot of excellent changes, among them some fine
work by Romain dealing with exactly that. Full announcement coming later once
I am back from running and kid's soccer game.

Dirk

-- 
Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com