[Rd] Issue with c++ .C call

[Thomas Lumley]

On Tue, 10 Jan 2006, Dominick Samperi wrote:

> 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

Not at all.  He is using .C, which passes a double * to the C function. 
You may be thinking of .Call

 	-thomas


> 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
>>
>> R is free software and comes with ABSOLUTELY NO WARRANTY.
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>> Type 'license()' or 'licence()' for distribution details.
>>
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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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>
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Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle