Even though the C99 standard allows variable length arrays on the stack, I would avoid using them much as the stack is a much more limited resource than the heap (where malloc allocates memory). A typical stack has a few megabytes while a typical heap has a few gigabytes. Detecting stack overflows can be hard.
Bill Dunlap TIBCO Spotfire wdunlap tibco.com -----Original Message----- From: r-devel-boun...@r-project.org on behalf of Murray Efford Sent: Sat 9/26/2009 3:25 AM To: Prof Brian Ripley Cc: r-de...@lists.r-project.org Subject: Re: [Rd] Compatibility of external C code across platforms Thank you. I'm much clearer on this. I now notice that the messages from gcc distinguish breaches of ISO C and ISO C90, and can see the significance. My gcc versions were the same - the different behaviour is likely to be explained by the --std flag. And it looks like I have to re-write a lot of C to eliminate nesting of functions. Point taken about HTML. Murray Efford ________________________________________ From: Prof Brian Ripley [rip...@stats.ox.ac.uk] Sent: Saturday, 26 September 2009 9:40 p.m. To: Murray Efford Cc: r-de...@lists.r-project.org Subject: Re: [Rd] Compatibility of external C code across platforms On Sat, 26 Sep 2009, Murray Efford wrote: > A package I have written makes considerable use of external C code. > There appear to be no problems building a Windows binary with the > GNU C compiler, but now I would like to make the package available > for other platforms. A stringent check of the code with the gcc > options '-Wall -pedantic' flags many nested functions and > variable-length arrays that are not allowed in ISO C. Is it > essential that distributed C source code for R packages conforms to > ISO C in this respect? I'm working in Windows XP with R2.9.2 and > Rtools 2.9. Yes, it is essential. R does not assume gcc, and it does not even assume gcc 4.x (and people are still using gcc 3.x on some platforms, e.g. the sunfreeware R builds). This is why we publish test result on CRAN for a completely different compiler (from SunPro). However, if is not clear which standard you mean by 'ISO C': assuming C99 is fairly safe, but GNU extensions from C99 are not -- nested functions are one such. > [Incidentally, when I use a makevars.win file to include these gcc > options in Rcmd build etc. the problem with variable-length arrays > is not flagged; maybe my command-line gcc is a different version > from that in Rtools] Well, you (and only you) can easily check that for yourself, but the other flags also matter, especially --std. Because it has been needed for the use of the MinGW headers, R on Windows is built with --std=gnu99. (Linux headers have a similar problem: using --std=c99 disables some features we test for in configure and wish to use -- and there are OS features, not language extensions.) > > Murray Efford > University of Otago > Dunedin, New Zealand > murray.eff...@otago.ac.nz<mailto:murray.eff...@otago.ac.nz> > > [[alternative HTML version deleted]] Please note what the posting guide has to say about that. > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > -- Brian D. Ripley, rip...@stats.ox.ac.uk 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 [[alternative HTML version deleted]] ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
