[R-pkg-devel] C++ library USING_R

*Please* direct this back to the list if you have another follow-up. Private
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On 15 October 2020 at 07:53, Joseph Park wrote:
| Thanks for the clarification.
|
| One last caveat: the C++ code already has a hook presuming #define
| USING_R. Does it seem reasonable/safe to use that as the variable passed
| to the C++ library build instead of say R_BUILD?

Hm, here I do not understand how you think that a _constant_ declaration can
help you detect a _variable_ situation ("are we / are we not compiled for R").

If you mainly wonder about the name of the variable: your code. You can do
what you want. Nobody cares. No "defaults".
  
| Or, does defining USING_R as an environment variable (-D) have potential

-D is not an envinronment variable.

-D is a #define passed tot he compiler.

| unintended consequences since the R headers already have defined it?? I
| would think it's OK since the library/build is "independent" from R.

A build triggered from src/Makevars is NOT independent of R.
  
| As a disciple of PEP20, I suppose (re)defining USING_R for specific
| purposes is a bad idea...

I have no idea what PEP20 is. I helped you from an R list. Do not assume I
know (Python?) lingo.

Dirk
  
| J Park
|
| On 10/15/20 7:32 AM, Dirk Eddelbuettel wrote:
| > (Replies on-list preferred)
| >
| > On 15 October 2020 at 07:08, Joseph Park wrote:
| > | Thank you.? It always stings a bit to miss the obvious solution as you
| > | have suggested. :(
| >
| > No worries :)  R builds are "special" enough to warrant an iteration or two to
| > get familiar with the pecularities.
| >
| > | Yes, the C++ library is built during the R package install.
| > |
| > | We have in Makevars:
| > |
| > | all : $(SHLIB)
| > |
| > | $(SHLIB): $(LIBEDM)
| > |
| > | $(LIBEDM):
| > |  ??? @(cd $(CPPEDM_SRC_PATH) && $(MAKE) clean && $(MAKE) \
| > |  ??? CXX="$(CXX11) $(CXX11STD)" CXXFLAGS="$(CXX11FLAGS) $(CXX11PICFLAGS)" \
| > |  ??? AR="$(AR)" RANLIB="$(RANLIB)")
| > |
| > | The obvious solution is to add an environment variable in the LIBEDM
| > | build command, ala:
| > |
| > | R_BUILD=1
| > |
| > | Then the C++ code can use #ifdef R_BUILD ...
| > |
| > | Is this tenable, or, is there another preferred approach?
| >
| > No, that is what I would do as a -D.... option to the compiler call ie
| > directly add -DR_BUILD=1 here
| >
| > $(LIBEDM):
| >    ??? @(cd $(CPPEDM_SRC_PATH) && $(MAKE) clean && $(MAKE) \
| >    ??? CXX="$(CXX11) $(CXX11STD)" CXXFLAGS="$(CXX11FLAGS) $(CXX11PICFLAGS)" -DR_BUILD=1 \
| >    ??? AR="$(AR)" RANLIB="$(RANLIB)")
| >
| > or expand CXX11FLAGS with a += but then CRAN does not like us to use GNU Make
| > extensions so the above may be easiest.
| >
| > Dirk
| >
| > | Thanks!
| > |
| > | J Park
| > |
| > | On 10/14/20 9:40 PM, Dirk Eddelbuettel wrote:
| > | > On 14 October 2020 at 15:56, Joseph Park wrote:
| > | > | Dear R-devel,
| > | > |
| > | > | The Writing R Extensions manual states:
| > | > |
| > | > | 6.14 Platform and version information
| > | > | The header files define USING_R, which can be used to test if the code
| > | > | is indeed being used with R.
| > | > |
| > | > | I suppose this only applies to building R itself?? Or, perhaps when Rcpp
| > | > | is used for the interface, or if one includes R headers explicitly.
| > | > |
| > | > | I have a C++ library that is built with no R-dependencies, then wrapped
| > | > | with an Rcpp interface. This same library is wrapped with pybind11 in
| > | > | the Python world, and directly used in C++ applications.
| > | > |
| > | > | How can the C++ library code "know" that it's R building the library? Is
| > | > | there a platform-independent environment variable or macro?
| > | >
| > | > So if I have this right you have
| > | >
| > | >    - a library LIB using only standard C++ components
| > | >
| > | >    - that you wrapped into a Python package via pybind11, and
| > | >
| > | >    - that you want to build for R and 'let it know it used for R'
| > | >
| > | > Well I think you would then use a (wrapper) R package R_LIB and could set up
| > | > a -DR_BUILD in the src/Makevars for R_LIB. This presume that you actually
| > | > recompile LIB as part of the build; if you were to link with a static or
| > | > shared build then you could not do this _for lack of a subsequent
| > | > compilation_ and can only rely on run-time information.
| > | >
| > | > Hope this helps, and that I didn't misunderstand the question.
| > | >
| > | > Dirk
| > | >
| >
|