[R-pkg-devel] Calling R's tempdir() from C

Duncan Murdoch murdoch@dunc@n @ending from gm@il@com
Fri Aug 10 09:10:02 CEST 2018

On 10/08/2018 12:01 AM, Rodrigo Tobar wrote:
> Dear all,
> I want to create a temporary directory from within my C++ R extension.
> On the other hand, CRAN's policy dictates that one cannot write anything
> outside the boundaries of the session's temporary directory, so I need
> to create it exactly there.
> The R API offers R_tmpnam and R_tmpnam2, both of which require the path
> of the directory where the new name will reside. This can be obtained
> using tempdir() in R, but I couldn't find anything similar in the R API.
> Am I missing anything too obvious?

Why not pass the result of tempdir() in your call from R to your C++ 
function, or in an initialization call for your package?  It won't 
change during a session.

Duncan Murdoch

> I tried out giving a NULL dirname to R_tmpnam{,2}, hoping that even
> though it's not mentioned in the docs, they would internally use the
> session's tmp dir, but this simply crashed. When embedding R one could
> also use the R_TempDir global variable, but this is flagged as
> unofficial R API for extensions. Finally, the only solution I could find
> was to call the tempdir() R function from within my C++ extension. This
> works fine, but it bothers me that there not an equivalent entry point
> in R's API.
> Any pointers would be appreciated. If I'm deeply misunderstanding
> something please also shoot.
> Cheers,
> Rodrigo
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