On Mon, Mar 29, 2010 at 01:56:14PM +0200, Roger Bergande wrote: ... > 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.
I do not see this value printed in the examples below. So, i think you assume that 1204.245 was changed to 1204.2449999999999999 since rounding it to 2 digits produces 1204.24. The problem is indeed a rounding problem, but not when the number is passed to C. The number 1204.245 cannot be represented in double precision exactly. So, already at the R level is, actually formatC(1204.245, digits=20) # [1] "1204.2449999999998909" See http://rwiki.sciviews.org/doku.php?id=misc:r_accuracy or FAQ 7.31 for more examples. Petr Savicky. > > 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 > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel