[Rd] Issue with c++ .C call

[Dominick Samperi]

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

Dominick

Sean Davis wrote:
> I am still having some difficulties with connecting R to a C++ function.  I
> am able to call the function as expected after compiling the shared library
> and such.  However, the call to the function is via .C; parameters from the
> .C call are not being passed correctly to the function.  As an example, I
> have attached a GDB run of the code.  I set a breakpoint on entry to the
> function I am calling from R.  What is bothering me (and probably causing
> the segmentation faults I am seeing) is that the parameter
> prm=as.double(c(3.2,1.1)) is not 3.2,1.1 IMMEDIATELY after the call to .C.
> I am sure I am missing something very basic.
>
> Thanks,
> Sean
>
>
>   
>> sessionInfo()
>>     
> R version 2.2.0, 2005-08-11, powerpc-apple-darwin7.9.0
>
> attached base packages:
> [1] "methods"   "stats"     "graphics"  "grDevices" "utils"     "datasets"
> [7] "base"     
>
>
>
>
> holmes:~/Mercury/projects/R/StepGram sdavis$ R -d gdb
> GNU gdb 6.1-20040303 (Apple version gdb-413) (Wed May 18 10:17:02 GMT 2005)
> Copyright 2004 Free Software Foundation, Inc.
> GDB is free software, covered by the GNU General Public License, and you are
> welcome to change it and/or distribute copies of it under certain
> conditions.
> Type "show copying" to see the conditions.
> There is absolutely no warranty for GDB.  Type "show warranty" for details.
> This GDB was configured as "powerpc-apple-darwin"...Reading symbols for
> shared libraries ... done
>
> (gdb) r
> Starting program: 
> /Users/sdavis/R-devel2/R.framework/Versions/2.2.0/Resources/bin/exec/R
> Reading symbols for shared libraries ...........+ done
>
> R : Copyright 2005, The R Foundation for Statistical Computing
> Version 2.2.0 Under development (unstable) (2005-08-11 r35256)
> ISBN 3-900051-07-0
>
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>
> Reading symbols for shared libraries
> ............................................................. done
> Reading symbols for shared libraries . done
> Reading symbols for shared libraries . done
>   
>> dyn.load('StepGram/src/Stepgram.so')
>>     
> Reading symbols for shared libraries .. done
>   
>> mySG <- function(dat1,thresh,noise) {
>>     
>   vec <- c(thresh,noise)
>   .C('calcStepgram',
>      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)
>   
> Program received signal SIGINT, Interrupt.
> 0x9001f208 in select ()
> (gdb) break calcStepgram
> Breakpoint 1 at 0x10bb418: file Stepgram.cpp, line 22.
> (gdb) c
> Continuing.
>   
>> mySG(dat1=dat,thresh=3.2,noise=1.1)
>>     
>
> Breakpoint 1, calcStepgram (data=0x1137048, prm=0x1c81eb0,
> intervals=0xbfffd7e0, max=0x2954840, n=0xbfffd6c0, plot=0x180d574) at
> Stepgram.cpp:22
> (gdb) print prm[0]
> $1 = 1.7716149411915527e-303    <<<<<------This should be 3.2!
> Current language:  auto; currently c++
>
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