[R-pkg-devel] Unable to access log operator in C

[Dirk Eddelbuettel]

On 28 February 2024 at 19:05, Avraham Adler wrote:
| I am hoping the solution to this question is simple, but I have not
| been able to find one. I am building a routine in C to be called from
| R. I am including Rmath.h. However, when I have a call to "log", I get
| the error "called object 'log' is not a function or a function
| pointer. When I "trick" it by calling log1p(x - 1), which I *know* is
| exported from Rmath.h, it works.
| 
| More completely, my includes are:
| #include <R.h>
| #include <Rmath.h>
| #include <Rinternals.h>
| #include <Rconfig.h>
| #include <stdlib.h> // for NULL
| #include <R_ext/Rdynload.h>
| 
| The object being logged is a double, passed into C as an SEXP, call it
| "a", which for now will always be a singleton. I initialize a pointer
| double *pa = REAL(a). I eventually call log(pa[0]), which does not
| compile and throws the error listed above. Switching the call to
| log1p(pa[0] - 1.0) works and returns the proper answer.
| 
| Even including math.h explicitly does not help, which makes sense as
| it is included by Rmath.h.

Can you show the actual line?  Worst case rename your source file to end in
.cpp, include <cmath> and call std::log.

  > Rcpp::cppFunction("double mylog(double x) { return std::log(x); }")
  > mylog(exp(42))
  [1] 42
  > 

Dirk

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