Handling reals in Fortran together with R

Question

I am having trouble handling reals in Fortran, which I use together with R. The following code is written in Fortran:

Subroutine realtest(lol)
implicit none
Real         


        

Answer 1

Try using double precision instead of real; the following works for me:

! realtest.f90
!
subroutine realtest(x)
    implicit none

    double precision, intent(inout) :: x
    x = 10.0
end subroutine realtest

From R,

dyn.load("realtest.so") 
res <- .Fortran("realtest", x = as.double(1.2))
res
# $x
# [1] 10

Answer 2

You should declare lol as real*8 since R uses double-precision floating-point number.