On Mon, Sep 12, 2011 at 10:39:47AM -0700, Alan Irwin wrote:
> On 2011-09-12 13:10+0100 Andrew Ross wrote:
>
>>
>> Alan,
>>
>> Good idea. I was forgetting that you could redefine macros even after
>> they had been used in further #define statements.
>
> Hi Andrew:
>
> I assume you have thoroughly tested that assumption so it must be
> true, but that sure seems counter-intuitive to me, and I cannot find a
> reference to it. Furthermore, K&H "The ANSI C Programming Language",
> p. 89 state "subsequent occurrences of the token name will be replaced
> ....", and that "subsequent" adjective seems to contradict the assumption.
Well to be honest I was rather surprised that it worked as I'd always
assumed the contrary - which is why I didn't try this approach in the
first instance. Anyway, following your email I tested it (with gcc-4.5)
and it worked. Maybe this is a gcc feature? Anyway, the fix is limited
to gcc. Still, further testing on different versions would be wise.
You need to do something like
CFLAGS="-fvisibility=hidden" CXXFLAGS="-fvisibility=hidden" cmake ../plplot
to enable the gcc visibility options.
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.
> I now realize my previous idea implicitly depended on this assumption
> as well because oct-dlldefs.h modifies other macros within it
> depending on OCTAVE_EXPORT, and those won't get changed by my
> subsequent OCTAVE_EXPORT redefinition if the assumption is incorrect.
>
> If further testing shows this assumption doesn't really work, then I
> suggest a new idea which is we simply replace oct-dlldefs.h with our
> own modified version where the replace the present OCTAVE_EXPORT
> definition logic with the following logic (similar to what we do in
> pldll.h(.in)):
>
> #if defined (_MSC_VER)
> // Visual C/C++, Borland, MinGW and Watcom
> #if defined ( __VISUALC__ ) || defined ( _MSC_VER ) || defined ( __BORLANDC__ ) || defined ( __GNUC__ ) || defined ( __WATCOMC__ )
> #define OCTAVE_EXPORT __declspec(dllexport)
> #else
> #define OCTAVE_EXPORT
> #endif
> #elif defined ( __CYGWIN__ )
> #define OCTAVE_EXPORT __declspec(dllexport)
> #elif defined ( __GNUC__ ) && __GNUC__ > 3
> #define OCTAVE_EXPORT __attribute__ ( ( visibility( "default" ) ) )
> #endif
>
> #ifndef OCTAVE_EXPORT
> #define OCTAVE_EXPORT
> #endif
>
> The only further issue is our updated header has to be #included
> before any other octave header is #included (if the assumption fails).
> In swig use the following directives
>
> %begin %{
> #include "oct-dlldefs_modified.h"
> %}
>
> to accomplish that. The "#define octave_dlldefs_h 1" in our modified
> header that is copied from the original means that further #includes
> of oct-dlldefs.h effectively become preprocessor no-ops.
I think this is probably not necessary for now. I'd rather not do this
as it would be more work and might break with future octave versions.
> Even if the assumption that the last #define of some token completely
> supersedes previous #defines of that token is true so your present
> solution works, then I suggest you modify that present solution so you
> take full control of OCTAVE_EXPORT redefinition for all platforms
> using preprocessor language like what I use above for the hypothetical
> oct-dlldefs_modified.h.
My approach was to make minimal interference, but I agree it is probably
better to be consistent with pldll.h.
Andrew
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