On 2011-09-12 21:47+0100 Andrew Ross wrote: > The gcc manual seems to explain why this happens > http://gcc.gnu.org/onlinedocs/cpp/Object_002dlike-Macros.html#Object_002dlike-Macros > It works because all the occurences in oct-dlldefs.h are macros.
Hi Andrew: I have been exploring the question of whether this behaviour is a gcc idiosyncrasy or standard behaviour on my local LUG list, and someone there came up with the following reference: > Try going to http://gcc.gnu.org/c99status.html and clicking on link to N1256 to a pdf file is the closest thing I have. That context is important because that PDF doesn't really identify itself as c99 or a working draft of that standard. Anyhow, I assume it is a c99 working draft. I did find example 3 "to illustrate the rules or redefinition and reexamination" in section 6.10.3.5 of that document. That example shows a function-like macro that uses another object-like macro which is subsequently redefined, and that subsequent redefinition appears to prevail just like you have discovered in the present octave case. (I say "appears" here because I cannot seem to find a clear list of the redefinition rules in that rather opaque document.) So it appears the gcc preprocessor behaviour clearly documentated at http://gcc.gnu.org/onlinedocs/cpp/Object_002dlike-Macros.html#Object_002dlike-Macros is a c99 standard or at least consistent with a draft of that standard. Anyhow, that example in the PDF should reduce some of our concerns over using that same trick for dealing with gcc visibility issues with octave. > My approach was to make minimal interference, but I agree it is probably > better to be consistent with pldll.h. OK, "minimal interference" is also a good argument so I will be happy with whatever you ultimately decide to do here. I first really got involved with PLplot in 2000 with very little C knowledge at the time, and the C knowledge I have accumulated since then has been mostly self-taught. In my wildest dreams back then, I never would have thought that 11 years later I would be doing such exotic stuff as trying to figure out C preprocessor issues by consulting the standards! That's a perfect illustration of one of the advantages of joining free software development efforts such as PLplot --- You sure learn a lot. Best wishes, Alan __________________________ Alan W. Irwin Astronomical research affiliation with Department of Physics and Astronomy, University of Victoria (astrowww.phys.uvic.ca). Programming affiliations with the FreeEOS equation-of-state implementation for stellar interiors (freeeos.sf.net); the Time Ephemerides project (timeephem.sf.net); PLplot scientific plotting software package (plplot.sf.net); the libLASi project (unifont.org/lasi); the Loads of Linux Links project (loll.sf.net); and the Linux Brochure Project (lbproject.sf.net). __________________________ Linux-powered Science __________________________ ------------------------------------------------------------------------------ BlackBerry® DevCon Americas, Oct. 18-20, San Francisco, CA Learn about the latest advances in developing for the BlackBerry® mobile platform with sessions, labs & more. See new tools and technologies. Register for BlackBerry® DevCon today! http://p.sf.net/sfu/rim-devcon-copy1 _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
