On Sat, 26 Apr 2008, Ramon Diaz-Uriarte wrote: > On Sat, Apr 26, 2008 at 3:19 AM, Duncan Murdoch <[EMAIL PROTECTED]> wrote: >> Ramon Diaz-Uriarte wrote: >> >>> Dear All, >>> >>> In a package, I am using ".C" to call some C functions. In one case, >>> the number of elements of the return vectors are not known in R before >>> the C call. (Two of the vectors are integers, the third is vector of >>> character strings). >>> >>> Passing from R a vector of the maximum possible size would be a huge >>> waste. I understand one alternative is to use ".Call", but I'd rather >>> avoid it if I can (all of the code seems working except for the return >>> of values into R). Another would be to write to a file from C and then >>> read that into R, but this looks very ugly. Are there any other >>> reasonable alternatives, or should I just use .Call? >>> >>> >> >> .Call is usually easiest, but another possibility is to have two entry >> points: one to calculate how much space you need, a second to pass in a >> vector that's the right size to hold the result. >> > > > You mean making two successive calls to the C code? The problem is > that the size of the result is not known until the result is obtained > (in my C code, the underlying structure is a linked list that gets > stretched as needed as the computation proceeds). So I would not know > "where to leave the result from C" in between the two calls to C.
But that is possible (you malloc the memory for a local copy in the rist call), and rpart does something like it. -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
