R devel - Dec 2012 - reinterpreting externalptr in R

Hi,

I am using swig to build a wrapper for an c-function to use it in R. I would
like to define a generic function, which gives back a void pointer. On the R
side, I know what this pointer is pointing to, whether it is an integer or
an string, or something else... but I need to somehow reinterpret the
resulting "externalptr" into another form...

a function that looks like the following:

*void* test(){
    std::string str="test";
    return str.c_str();
}*

when I call this from R:

*str <- test()
typeof(str) % result is: "externalptr"*

how could I reinterpret this to a charcterarray, to a numeric, to list, or
...

Thanks for any suggestions ;)



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On Dec 25, 2012, at 6:39 AM, andre__ wrote:
> Hi,
> 
> I am using swig to build a wrapper for an c-function to use it in R. I
would
> like to define a generic function, which gives back a void pointer. On the
R
> side, I know what this pointer is pointing to, whether it is an integer or
> an string, or something else... but I need to somehow reinterpret the
> resulting "externalptr" into another form...
> 
> a function that looks like the following:
> 
> *void* test(){
>    std::string str="test";
>    return str.c_str();
> }*
> 
> when I call this from R:
> 
> *str <- test()
> typeof(str) % result is: "externalptr"*
> 
> how could I reinterpret this to a charcterarray, to a numeric, to list, or
> ...
> 
The simple answer is you can't. External pointers are entirely opaque to R,
so *you* have to write that code that interprets them. Obviously it's then
up to you to create the corresponding R object from the external pointer.

You may want to have a look at interface packages like Rcpp, rJava, Rserve, ...
to understand how objects are converted to/from other languages.

Cheers,
Simon


> Thanks for any suggestions ;)
> 
> 
> 
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> View this message in context:
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> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
>

Thanks a lot ... 





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