Debugging (line by line) of Rcpp-generated DLL under Windows

Recently I've been experimenting with Rcpp (inline) to generate DLLs that perform various tasks on supplied R inputs. I'd like to be able to debug the code in these DLLs line by line, given a specific set of R inputs. (I'm working under Windows.)

To illustrate, let's consider a specific example that anybody should be able to run...

The code below is a really simple cxxfunction which simply doubles the input vector. Note however that there's an additional variable myvar that changes value a few times but doesn't affect the output - this has been added so that we'll be able to see when the debugging process is running correctly.

library(inline)
library(Rcpp)

f0 <- cxxfunction(signature(a="numeric"), plugin="Rcpp", body='
    Rcpp::NumericVector xa(a);
    int myvar = 19;
    int na = xa.size();
    myvar = 27;
    Rcpp::NumericVector out1(na);
    for(int i=0; i < na; i++) {
        out1[i] = 2*xa[i];
        myvar++;
    }
    myvar = 101;
    return(Rcpp::List::create( _["out1"] = out1));
')

After we run the above, typing the command

getLoadedDLLs()

brings up a list of DLLs in the R session. The last one listed should be the DLL created by the above process - it has a random temporary name, which in my case is

file7e61645c

The "Filename" column shows that cxxfunction has put this DLL in the location tempdir(), which for me is currently

C:/Users/TimP/AppData/Local/Temp/RtmpXuxtpa/file7e61645c.dll

Now, the obvious way to call the DLL is via f0, as follows

> f0(c(-7,0.7,77))

$out1
[1] -14.0   1.4 154.0

But we can of course also call the DLL directly by name using the .Call command:

> .Call("file7e61645c",c(-7,0.7,77))

$out1
[1] -14.0   1.4 154.0

So I've reached the po

Edit Report

I am a little stunned by the obsession some Rcpp users have with the inline package and its cxxfunction(). Yes, it is indeed very helpful and it has surely has driven adoption of Rcpp further as it makes quick experimentation so much easier. Yes, it allowed us to use 700+ unit tests in the sources. Yes, I use it all the time to demonstrate examples here, on the rcpp-devel list or even live in presentations.

But does that mean we should use it for each and every task? Does it mean that it does not have "costs" such as randomized filenames in a temporary directory etc pp? Romain and I argued otherwise in our documentation.

Lastly, debugging of dynamically loaded R modules is difficult as it stands. There is an entire section in the (mandatory) Writing R Extensions about it, and Doug Bates once or twice posted a tutorial about how to do this via ESS and Emacs (though I always forget where he posted it; once was IIRC on the rcpp-devel list).

Edit 2012-Jul-07:

Here is your step by step:

(Preamble: I've used gcc and g++ for many years, and even when I add -g I don't always turn -O2 into -O0. I am really not sure you need that, but as you ask for it...)
Set your environment variable CXXFLAGS to "-g -O0 -Wall". There numerous ways to do it, some are platform-dependent (eg Windows c

answered 2012-07-06T13:26:05.440

Debugging (line by line) of Rcpp-generated DLL under Windows

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