[R-pkg-devel] Link compiled C object to internal package file

[Martin Morgan]

Section 1.2 of 'Writing R Extensions' says

Another example is when a package installs support files that are required at run time, and their location is substituted into an R data structure at installation time. The names of the top-level library directory (i.e., specifiable via the ‘-l’ argument) and the directory of the package itself are made available to the installation scripts via the two shell/environment variables R_LIBRARY_DIR and R_PACKAGE_DIR. Additionally, the name of the package (e.g. ‘survival’ or ‘MASS’) being installed is available from the environment variable R_PACKAGE_NAME. (Currently the value of R_PACKAGE_DIR is always ${R_LIBRARY_DIR}/${R_PACKAGE_NAME}, but this used not to be the case when versioned installs were allowed. Its main use is in configure.win scripts for the installation path of external software’s DLLs.) Note that the value of R_PACKAGE_DIR may contain spaces and other shell-unfriendly characters, and so should be quoted in makefiles and configure scripts

which sounds approximately similar to your situation and suggests using the full path to the installed file R_PACKAGE_DIR/dict/<myfile.ext>.

It's not really clear what your two use cases are below, specifically the unique circumstances of 'in tests only'. I would guess that a relative path would not work, in general, because the path would be relative to the current working directory, which of course changes, rather than relative to the path of the shared object...

Martin Morgan

On 6/19/19, 10:46 AM, "R-package-devel on behalf of mark padgham" <r-package-devel-bounces using r-project.org on behalf of mark.padgham using email.com> wrote:

    Yeah, but that would require completely rewriting the C code to accept a
    variable for something that is used hundreds of times as a simple macro.
    (Most of that C code is an old library bundled with the package, so not
    my work in that regard.) It would still be enormously easier to robustly
    provide a relative location within the compiled source object to direct
    it to the file ... but how?
    
    
    On 19/06/2019 14:10, Jeff Newmiller wrote:
    > What do you mean by
    >
    > "call an external text file"
    >
    > ? Text files are data... do you want to open it and read it? Are you familiar with the system.file() function?
    >
    >
    > On June 19, 2019 5:45:51 AM CDT, mark padgham <mark.padgham using email.com> wrote:
    >> Dear All,
    >>
    >> I'm developing a package which primarily relies on C code that itself
    >> has to call an external text file representing a dictionary or lookup
    >> table. The location of this file is defined in a C macro, the file
    >> itself packaged in "./inst/dict/<myfile.txt>" and so currently called
    >> as
    >> "#define mylocation './dict/<myfile.txt>'". I can load the package and
    >> all works well, yet the tests fail because the compiled object
    >> ("./src/<myobject.so>") can not find this file **in tests only**. My
    >> primary request would then be advice for where best to place such files
    >> that need to be called directly by compiled objects, and how to direct
    >> the compiled object to such files? Failing that, advice on why such
    >> attempts at linking compiled objects to external files might fail only
    >> during tests, yet work otherwise, would be appreciated.
    >>
    >> Other important info: Yes, the external dictionary file **must** be
    >> linked directly from the compiled object, not at run time. This means
    >> that no R-based solutions can be implemented, and so the problem can
    >> only be solved in this case through figuring out how to direct a
    >> compiled object to connect to an additional package-internal file.
    >>
    >> Thanks in advance,
    >>
    >> mark
    >>
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