c File name: call_f.f
c For dynamical loading, compile by g77.
c SHELL> g77 -c call_f.f ; g77 -shared -o call_f.so call_f.o

      subroutine hello(m, a, b, c, d)
        integer i, m
        real*8 a(m), b(m), c(m), d

        d = 0
        do i = 1, m
          c(i) = a(i) + b(i)
          d = d + c(i)
          a(i) = 0
        end do

        return
      end

c Output is a shared library "call_f.so" can called by R.

c File name: call_f.f
c For dynamical loading, compile by Compaq Visual Fortran.
c Here, for fortran 77 syntex.

      subroutine hello(m, a, b, c, d)
cDEC$ ATTRIBUTES DLLEXPORT::hello
cDEC$ ATTRIBUTES C, REFERENCE, ALIAS:'hello_'::hello
        integer i, m
        real*8 a(m), b(m), c(m), d

        d = 0
        do i = 1, m
          c(i) = a(i) + b(i)
          d = d + c(i)
          a(i) = 0
        end do

        return
      end

c Output is a shared library "call_f.dll" caned call by R.
c For fortran 90 syntex, use "!DEC$" to replace "cDEC$".

# File name: call_f.r

dyn.load("call_f.so")
# For Windows will like this
# dyn.load("C:/Windows/Desktop/call_f.dll")

symbol.For("hello")
is.loaded(symbol.For("hello"))

a <- 1 : 9

test.f <- function(a) {
  b <- a
  d <- vector(mode = "numeric", length = length(a))
  e <- vector(mode = "numeric", length = 1)
  ret <- .Fortran("hello", m = length(a), a = as.double(a),
           b = as.double(b), d = as.double(d), e = as.double(e))
  ret
}

test.f(a)

dyn.unload("call_f.so")
# For Windows will like this
# dyn.unload("C:/Windows/Desktop/call_f.dll")

/*
  File name: call_c.c
  For dynamical load compile by gcc.
  SHELL> gcc -c call_c.c ; gcc -shared -o call_c.so call_c.o
*/

void hello(int m, double *a, double *b, double *c, double *d){
  int i;

  d = 0;
  for(i = 0; i < m; i++){
    c[i] = a[i] + b[i];
    *d =+ c[i];
    a[i] = 0;
  }
}

/* Output is a shared library "call_c.so" can called by R. */

# File name: call_c.r

dyn.load("call_c.so")
# For Windows will like this
# dyn.load("C:/Windows/Desktop/call_c.dll")

symbol.C("hello")
is.loaded(symbol.C("hello"))

a <- 1 : 9

test.c <- function(a) {
  b <- a
  d <- vector(mode = "numeric", length = length(a))
  e <- vector(mode = "numeric", length = 1)
  ret <- .C("hello", m = length(a), a = as.double(a),
           b = as.double(b), d = as.double(d), e = as.double(e))
  ret
}

test.c(a)

dyn.unload("call_c.so")
# For Windows will like this
# dyn.unload("C:/Windows/Desktop/call_c.dll")

$m
[1] 9

$a
[1] 0 0 0 0 0 0 0 0 0

$b
[1] 1 2 3 4 5 6 7 8 9

$d
[1]  2  4  6  8 10 12 14 16 18

$e
[1] 90