R devel - Mar 2013 - compiling C code using headers from another R package

I am developing an R package, eiR,  which depends on another C library, 
GNU scientific library (GSL). In order to make life easier for the user, 
it would be nice to not have this as an external dependency, thus I 
would like to wrap this library in another R package, say GSLR for 
example. Thus far I know how to do this. The C code in eiR requires the 
.so library and the header files from GSL in order to compile. So the 
idea is that eiR would depend on GSLR, then GSLR gets compiled and 
installed first, then, while eiR is installing, it should be able to 
make use of the GSL library and header files while compiling. So my 
question is, how do I know where the GSL library and header files, 
packaged in GSLR, would live so I can point the compiler at them? I know 
how to find the installed directory of an R package from within R, but 
is there way to find that out using just Makevars or a Makefile? I'm 
open to suggestions about a better way organize all of this as well. I 
like the idea of keeping the GSL code separate so that it can be 
updated/changed independently from eiR though.
     I'm also aware of the gsl R library on CRAN, however, this just 
wraps GSL in R functions, but I need to use the GSL C functions in other 
C code in eiR.

Thanks.

Kevin

Kevin,

On Mar 11, 2013, at 5:20 PM, Kevin Horan wrote:
> 
> I am developing an R package, eiR,  which depends on another C library, GNU
scientific library (GSL). In order to make life easier for the user, it would be
nice to not have this as an external dependency, thus I would like to wrap this
library in another R package, say GSLR for example. Thus far I know how to do
this. The C code in eiR requires the .so library and the header files from GSL
in order to compile. So the idea is that eiR would depend on GSLR, then GSLR
gets compiled and installed first, then, while eiR is installing, it should be
able to make use of the GSL library and header files while compiling. So my
question is, how do I know where the GSL library and header files, packaged in
GSLR, would live so I can point the compiler at them? I know how to find the
installed directory of an R package from within R, but is there way to find that
out using just Makevars or a Makefile? I'm open to suggestions about a
better way organize all of this as well. I like the idea of keeping the GSL code
separate so that it can be updated/changed independently from eiR though.
Have a look at Rcpp.

>    I'm also aware of the gsl R library on CRAN, however, this just
wraps GSL in R functions, but I need to use the GSL C functions in other C code
in eiR.
> 
Why is what you are proposing any better than simply using GSL in eiR? You will
still need the GSL external dependency for GSLR and you are only adding a lot of
complexity by linking into another package's external directory (you cannot
use libs) which is in itself very tricky (you'll have to deal with both
static and shared version, multi-arch setups, possible relocation etc.). It
won't make it any easier on the user, rather to the contrary as there will
be more things to break. The only reason Rcpp goes into such length to do this
is because it has no choice (the Rcpp library has to use the same libR so cannot
be used as external dependency) - I would certainly not recommend it for
something as trivial as providing GSL.

Cheers,
Simon

> Thanks.
> 
> Kevin
> 
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