returning vectors of unknown size from C (with .C)
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. Duncan Murdoch
Thanks, R.