[Rd] interaction with C++ code (PR#10487)

[Simon Urbanek]

This is a bug, but not in R, it's in your program:

On Dec 3, 2007, at 9:45 AM, I.J.Wilson at ncl.ac.uk wrote:

> Full_Name: Ian Wilson
> Version: 2.6.1
> OS: linux
> Submission from: (NULL) (128.240.229.7)
>
>
> The problem is new to R2.6.?.  The code works as expected in R-2.5.0.

it still does in 2.6.x - but it depends on what you expect. You fail  
to terminate the strings, so you get trailing garbage - it just may  
have happened that by chance the trailing memory was zero in 2.5.


> I get the
> problem with two different operating systems - an older redhat and  
> new ubuntu
> and with both g++4.1 and g++3.4.
>
> I have a problem with character data that is passed back from C++  
> code.  A small
> example is the following C++ code and R functions.
>
> #include <sstream>
> extern "C" {
>  void extracttxt( char **txt, int *nchars) {
>      std::ostringstream oss;
>      oss << "abcdefghij";
>      const char *ltxt=oss.str().c_str();
>      for (int j=0;j<*nchars;j++) *txt[j]=static_cast<char>(ltxt[j]);

As said above, you fail to terminate the string, you want to add  
something like:
        txt[j][1]=0;
here.

Cheers,
Simon

>
>    }
> }
>
> # begin R code
> dyn.load("test.so")
>
> "testtxt" <-  function() {
>  nchars <- 80
>  txt <- .C("extracttxt"
>            ,character(nchars)
>            ,as.integer(nchars))[[1]]
>
> txt
> }
> a=testtxt()
> a[1:10]
>
> # typically the results are something like
> [1] "a"                   "b\033\xba\bfaul\030" "cz#\b"
> [4] "d"                   "e"                   "f"
> [7] "g"                   "h"                   "i"
> [10] "j"
>
> or
> [1] "az#\b"            "b"                "c"                "d"
>
> [5] "e"                "f"                "g"                "h"
>
> [9] "i"                "j1\xba\brese\030"
>
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