Le 29/09/13 20:36, Simon Zehnder a écrit :
Hi Romain,
thanks for this fix!
On Sep 29, 2013, at 5:26 PM, Romain Francois <[email protected]> wrote:
Hello,
What acts as a proxy for const CharacterVector& does not do its proxy job.
Instead it gives direct access to the underlying array of SEXP that character
vector use.
I need some time to get this from the Rcpp source code to see what exactly is
going on there - I don't have this deep understanding of the class structure,
yet.
You don't really need to understand how it is implemented.
This has been fixed in Rcpp11. The relevant addition is the const_string_proxy
class. See this commit which can easily be applied to Rcpp.
https://github.com/romainfrancois/Rcpp11/commit/f5e1600f7acbf3bef39325c06ef3ac5ddf8dc66a
Your new rep Rcpp11 looks very interesting! I have to distribute my package not
on CRAN, but at least to colleagues working on Windows machines using the
Rtools package. Rtools relies on gcc 4.6 and from
http://gcc.gnu.org/projects/cxx0x.html I conclude, that it does not support all
features - I guess for Rcpp11 it needs at least gcc 4.7?
On my own machine I can use it without a problem, but for the distribution
among the Windows machines I fear I have to rely on the Rcpp CRAN version and
use the nonconst reference as parameter.
I am curious, what feature of C++11 does enable the const_string_proxy?
The commit in Rcpp11 also has removed a few things from the proxy class that I
don't judge needed anymore because I'm cleaning things. This might not apply to
Rcpp with its more strict compatibility requirements.
I see, that the class 'generic_proxy' has gone. What was its intention in Rcpp?
I don't think so. These classes implement a proxy pattern. That is
classic c++ pattern.
In essence, when you have a List and you call its operator[], what you
get is a generic_proxy. This class's job is to define getters and
setters in terms of operator= and implicit conversion operators so that
you can do things like this:
List z ;
RObject x = z[0] ;
z[0] = 2 ;
The proxy classes take care of all the plumbing here.
But again, you should not need to know about this.
Best
Simon
Romain
Le 29/09/13 15:24, Romain Francois a écrit :
Le 29/09/13 14:06, Simon Zehnder a écrit :
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));
}
Try actually using the variable you pass in, as in:
void test2 (const Rcpp::CharacterVector &str)
{
Rprintf("test2: %s\n", (char*) str(0));
}
Although it still exposes the bug.
You can use something like this in the meantime:
void test2 (const Rcpp::CharacterVector& charv)
{
String x = charv[0] ;
Rprintf("test2: %s\n", x.get_cstring());
}
It looks like the bug is about converting the result of charv(0) to a
char*. Probably worth looking at the string_proxy class.
Romain
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?
Best
Simon
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
_______________________________________________
Rcpp-devel mailing list
[email protected]
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
_______________________________________________
Rcpp-devel mailing list
[email protected]
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
