Issue with c++ .C call

Sean,

prm in your function calcStepgram is NOT a vector of doubles, it is of type
SEXP, and you need to use R macros to fetch the value(s). This is done
automatically in the Rcpp package, and if you want to see how this is
done look at the definition of the class RcppVector in Rcpp.cpp

I'm not sure why the prm parameter is not a vector; I thought this was the
standard way to create a vector of doubles....  So to confuse myself even
more, I have added a simple C function that looks simply calls my C++
function like this:

extern "C" {
  void mymain(double *data,double *prm, double* intervals, int* max, int *n,
double *plot) {
    calcStepgram(data,prm,intervals,max,n,plot);
  }
}

Then, I call this function using .C('mymain',...) as before.  Note the
change in parameter memory locations from the call to mymain and the call to
calcStepgram.  Why does this happen?

dyn.load('StepGram/src/Stepgram.so')
mySG <- function(dat1,thresh,noise) {

vec <- c(thresh,noise)
  .C('mymain',
     data=as.double(dat1),
     prm=as.double(vec),
     intervals=double(10000*3+1),
     max=as.integer(10000),
     n=as.integer(length(dat1)),
     plot=double(length(dat1)))}

dat <- c(0.01,0.1,-0.2,0.1,-0.1,-1000,3.2,3.5,-1.3,

3.1,3.2,3.1,-0.1,0.2,0.15,-0.05,-0.1,0.2,0.1,-0.1)

....

(gdb) break mymain
Breakpoint 1 at 0x10c13f0: file Stepgram.cpp, line 23.
(gdb) c
Continuing.

mySG(dat1=dat,thresh=3,noise=1)

Breakpoint 1, mymain (data=0x1137148, prm=0x195cd30, intervals=0x1386018,
max=0x1b208e0, n=0x1b20900, plot=0x1137208) at Stepgram.cpp:23
23          calcStepgram(data,prm,intervals,max,n,plot);
(gdb) print prm[0]
$1 = 3
Current language:  auto; currently c++
(gdb) print prm[1]
$2 = 1
(gdb) print max[0]
$3 = 10000
(gdb) s       
calcStepgram (data=0x1137148, prm=0x180da24, intervals=0x195cd68,
max=0x1999d6c, n=0xbfffd6e0, plot=0x0) at Stepgram.cpp:29
29          Stepgram* sg=new Stepgram(data, *n);
(gdb) print prm[0]
$4 = 2.0002441518028817
(gdb)