On: Tuesday, July 23, 2013 1:14 PM Dirk Eddelbuettel [mailto:e...@debian.org] wrote:
> > On 23 July 2013 at 11:50, Steve Jaffe wrote: > > According to the C standard, it is safe to call free on a null pointer. > > Similarly, according to the C++ standard, it is safe to call 'delete' > > on a null pointer. > > Thus there is no need ever to test a pointer for null before > > free-ing/delete-ing. > > ... > > Thanks for the correction. I obviously shouldn't have mixed malloc/free with > new/delete in the discussion. > > I rarely need to write code that uses new/delete these days as I much prefer > to rely on STL containers -- a programming style advocated by just about > every modern C++ text (incl Stroustrup, 2013, 4th ed). And by just about all > Rcpp examples we provide. > > Dirk I agree that STL containers should be used whenever possible and new/delete avoided whenever possible. However, there are times when explicit 'new' cannot be avoided (I'm now referring only to C++.) In those cases the best way to avoid the need for explicit memory management is to use an appropriate "smart pointer" such as boost::shared_ptr (std::shared_ptr as of C++11). Then one never has to explicitly call 'delete.' To clarify, though: what I said originally about NULL pointers applies to both C (malloc/free) and C++ (new/delete). I know there is a lot of code where people check for null pointers before calling free or delete (I know -- I wrote a bunch of that code when I first started programming C/C++ :-) But it turns out that check is completely unnecessary. It is perfectly ok to call "free(0)" or "delete (char*)0" (although obviously no-one would write those explicitly.) This will *not* cause a core-dump (at least not with a standard-conforming compiler.) (I think the "legend" that it's bad to call 'free' on a null pointer may be based on some early C compilers, perhaps before the ANSI C standard...) I apologize for belaboring the point; I'm doing so only because this seems to be something that is often misunderstood, especially by newcomers to C/C++; and such misunderstanding can lead to someone wasting time when looking for the cause of a crash. References: C: Kernighan and Ritchie, The C Programming Language (2nd Ed), Appx B: "void free(void *p) free deallocates the space pointed to by p; it does nothing if p is NULL." C++: http://www.parashift.com/c%2B%2B-faq-lite/delete-handles-null.html Steve Steve Jaffe sja...@riskspan.com _______________________________________________ Rcpp-devel mailing list Rcpp-devel@lists.r-forge.r-project.org https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel
