To the C/C++ gurus here: Because of all the gcc warnings and g++ errors (more about that later) I was getting unless I used explicit casts with e.g, const PLFLT ** arguments I became concerned that perhaps I was misinterpreting the meaning of
const PLFLT ** z; Some googling this morning found the answer at http://stackoverflow.com/questions/336585/what-does-a-const-pointer-to-pointer-mean-in-c-and-in-c The discussion there pointed to http://c-faq.com/decl/spiral.anderson.html which I think you will all find an interesting read. Both sources confirm my original interpretation was correct. The answer is z is a mutable pointer to a mutable pointer to an immutable PLFLT. Therefore, such declarations for our function arguments claim that our functions are not changing the values of the doubly dimensioned z array which I believe is exactly what we want. Similarly, const PLFLT *x; arguments for our functions claim that our functions are not changing the values of the singly dimensioned x array which again I believe is exactly what we want. The above is useful background to the fundamental issue that bothers me which is automatic casting from mutable to immutable of singly dimensioned and doubly dimensioned arrays are treated quite differently by both gcc and g++. For an example of this with plline3, see examples/c/x18c.c where mutable x, y, and z singly dimensions array arguments are automatically cast to immutable without a warning message. I think that lack of warning message is the correct thing to do since obviously x, y, and z must be assigned values before calling plline3 so it makes no sense for gcc to warn about the automatic casting of each of those PLFLT * arrays to const PLFLT *. However, such sanity does not prevail for the doubly dimensioned array case; there you must explicitly use (const PLFLT **) casts to avoid warning messages from the gcc C compiler and error (!) messages from the gcc C++ compiler for the doubly dimensioned arrays, see examples/c/x11c.c and examples/c++/x11.cc. Does any C/C++ guru here know how to avoid those explicit casts for each of our doubly dimensioned arguments? I don't think I should revert the const project since there are reasons of documentation and safety to justify it (see http://www.cprogramming.com/tutorial/const_correctness.html). Nevertheless, if those explicit casts are required it will be inconvenient for our users so if it is possible to avoid that work, let's help at least our new users out with good examples. Note, this doubly dimensioned issue may be just a quirk with gcc and g++ being inconveniently restrictive about automatic casting from PLFLT ** to const PLFLT** without a warning (gcc) or error (g++) message, and other C and C++ compilers may have different quirks or errors concerning the interpretation of const. So it would be a good idea for those here with access to non-gcc compilers to run the test_diff_psc target with BUILD_TEST=ON and report back all warning or error messages that are related to our const arguments. Better to find out now about any platform problems introduced by the const modifier project rather than one day after our next release! 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); PLplot scientific plotting software package (plplot.org); 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 __________________________ ------------------------------------------------------------------------------ Colocation vs. Managed Hosting A question and answer guide to determining the best fit for your organization - today and in the future. http://p.sf.net/sfu/internap-sfd2d _______________________________________________ Plplot-devel mailing list Plplot-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/plplot-devel
