[Rcpp-devel] How to link a .lib file in a rcpp-package in a Windows environment?

Bernhard Pollner bernhard at bpollner.net
Sun Apr 24 22:26:13 CEST 2011

Hello Dirk,

thanks for your quick answer.
Due to my, unfortunately, profound lack of knowledge in this area I have to ask some additional (and probably quite stupid) questions regarding what you replied to me - see in the text below.

Am 24.04.2011 um 20:12 schrieb Dirk Eddelbuettel:

> Hi Bernhard,
> Thanks for posting here!
>> On 24 April 2011 at 18:29, Bernhard Pollner wrote:
>> | Hello,
>> | 
>> | I am in the process, i.e. I just began to write a Rcpp-based package for a
>> | Windows environment. The purpose of that package will be to read out signals
>> | from a USB-connected hardware. The company who is selling this hardware is
>> | distributing a SDK for developing custom C-programms to read out those signals,
>> | so I have all the required files (.h, .lib, .dll) to compile a working .exe
>> | file -- and now, due to some reasons, I want to implement this code in an
>> | R-package, and read out the signals from the devices straight from within R.
> I have done something similar in the part: use the .lib (or .dll) of a C
> library, presumably produced by a variant of Visual C++, in some MinGW
> compiled code for R.  With C you can do this; with C++ you are most often out
> of luck due to name mangling of the functions.
> The actual act of mixing MinGW and a VC library is a topic in and by itself;
> I have found the MinGW documentation to be of help. I believe the FAQ has an
> entry for this.  As I recall, you may need to do something about symbols
> being exported etc pp.

OK, so I will check the FAQs of the MinGW documentation.

> I would also strongly recommend to just write a simple 'hello world' wrapper
> that just tries to access one function from the SDK via R first, ie outside
> of Rcpp.  Once you have that working, mix it with Rcpp.

How do I write a simple wrapper via R  (without using Rcpp) for a function from the SDK? Or where can I start reading how to do that? 
Could you give me or point me to a code-example?

> The simplest use is to just drop the static library, with its full path, in
> the linker instructions.  So instead of  -lfoo  just do  C:/foo/sdk/lib/libfoo.a
> (and a relative path should work too).

The "linker instructions", are they written in the file Makevars.win? If not, where are they?
So, then in the right place, what EXACTLY should I then write in there for the .lib called e.g. "plastic.lib"?
(And how do I write relative paths?)

>> | I am planning to expose the needed C-functions via modules to R, but,
>> | unfortunately, I did not even come that far:
>> | 
>> | Here´s my problem:
>> | I do not know, i.e. it is not clear to me how to link / use the .lib file of
>> | the SDK in my package.
>> | (In the instructions coming with the SDK they write:  "... copy the contents of
>> | "API \ lib" to your compiler´s lib directory)
>> | Is it possible that I have to use the LDFlags function in src/Makevars.win here
>> | somehow? If yes, then I do not know how to write the appropriate code....
>> | I do have two .dll files (which I place in in the src-folder) and I suppose
>> | that I just write them into the Namespace-file using "useDynLib(NameOfTheFile)
>> | ".
>> | But, as I was not able to compile the package yet, I do not know if this is
>> | right either...
>> | (And the .h file I just put into the src-folder....)
>> | 
>> | Could someone, please, show me a way and  the code of how to correctly link the
>> | .lib file in my package?
> All that R does (in the simple cases) is to use it own rules, augmented by
> the instructions in the file  src/Makevars.win.
> So once you know how to build against the SDK (see above),
--- that means, once the missing .lib - file is correctly linked, or? -- 

> just follow the
> usual 'how to build your package with Rcpp' guidelines in the Rcpp-package
> vignette and expand PKG_LIBS and PKG_CXXFLAGS in src/Makewin.

Sorry, and again my knowledge in this field is rather bad:
how do I expand those flags, how do I add PKG_CXXFLAGS to the Makevars.win file?
Could you give me, please, an exact example of what I would have to write for a library called e.g. "plastic.lib"?

> Hope this helps,  Dirk

Thank you very much for your efforts,
with kind regards,

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