---------- Forwarded message ----------
From: roger.berga...@swisslife.ch
Date: Mon, 29 Mar 2010 13:51:12 +0200
Subject: .Call and .C arguments
To: berga...@gmail.com
Dear List
My question is about .C and .Call
I was experimenting with the .C and .Call interface as I came across the
following behaviour.
The passed values are not the same in C. I 'm calling a function in C
with the argument as.double(1204.245) but in the debug mode in C the
value has changed to 1204.2449999999999999.
Is there a way to pass the arguments differently?
I'm using Windows and Visual Studio C++ 2005 Express Edition and
R-2.10.1.
Please see the two simple examples to understand the issue.
# C call from R
.C("myroundC",as.double(1204.245))
// C Code
void myroundC(double *Amount){
*Amount = Rf_fround(*Amount,2);
}
#Return value in R
[[1]]
[1] 1204.24
# C call from R
.Call("myroundCall",as.double(1204.245))
// C Code
SEXP myroundCall(SEXP a){
double *ap = REAL(a), *ansp;
SEXP ans;
PROTECT(ans = allocVector(REALSXP, 1));
ansp = REAL(ans);
*ansp = Rf_fround(*ap,2);
UNPROTECT(1);
return(ans);
}
#Return value in R
[1] 1204.24
# expected value 1204.25
Thanks a lot for your help.
Best regards
Roger Bergande
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