[Rcpp-devel] useDynLib

[Davor Cubranic]

On 2011-03-31, at 8:12 PM, Sean Robert McGuffee wrote:

> Thanks for the info about modularity. I'll definitely be wikipedia'ing that.
> Also, thanks for clarifying the package author thing--I literally was
> imagining some sort of function that writes something related to packages.

You know, I can see that, esp. in the context of the rest of that section. I'll send a suggestion to the manual maintainers to consider using a clearer expression.

> In particular with useDynLib, what type of argument(s) go(es) in it?
> For example, do I literally copy a file object into it somehow?

What I have in my NAMESPACEs, and is used in the example in section 1.6.4 of the manual, is just the name of the DLL without the extension. And it's a symbol, rather than a string, so no quotes.

> For example, say I want to link against libpng14.
> On the machine I'm sitting at, it's located at:
> /usr/local/lib/libpng14.a
> How would I use useDynLib in that case?

Aha, you may not need to dive into "useDynLib"s dark corners after all. I only use "useDynLib" to link to my package's own library. For linking to a library provided by another package, such as Rcpp or a system library, I have a src/Makevars in my package that sets the right "-l" compiler switches and assigns them to PKG_LIBS variable. See section "1.2.1 Using Makevars" in R-exts. It goes into way more detail than you'll need (ignore all stuff about "configure" for now), or see how Rcpp.package.skeleton creates a Makevars file that has all the switches to link against Rcpp's DLL. (In their case it's a bit more general, and you may really need nothing more than "PKG_LIBS=-lpng14".)

I admit I approach this on a need-to-know basis myself, IOW only about as far as I need to make my code work. But it does work, and I have also seen it used in a number of packages I've looked at, so I don't think it's too far off the mark. Others on the list can chime in if I'm grossly misrepresenting the linking mechanism or what you should do in your case.

Davor