FYI, daily builds of RStudio now use libclang to provide way more C++ language support including autocomplete (but not, I believe, debugging).
http://www.rstudio.org/download/daily
// Preview Release Notes make a note of "Code completion for C/C++", but don't mention libclang (use of which is interesting on its own, IMHO, since it better indicates the quality improvement to expect): http://www.rstudio.com/products/rstudio/download/preview-rel...