Re: Anyone know of a C preprocessor #define introspection mechanism? (for FFI bindings)
- From: Steve Atkins <steve@xxxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Tue, 10 Feb 2015 18:18:43 -0800
On Feb 10, 2015, at 6:10 PM, demetri <demetri.spanos@xxxxxxxxx> wrote:
> Sorry, I know this is an odd question, but having a positive answer
> would greatly simplify some of our automated FFI code generation.
>
> I would like some way to detect at compile time that a preprocessor
> constant, say, AF_INET, is defined and automatically emit a line like
>
> int lj_ffi_cpp_constant_AF_INET = AF_INET;
>
> so that I could then, in FFI code, do something like:
>
> whatever = ffi.C.lj_ffi_cpp_constant_AF_INET
>
> I realize this is a bit of a stretch but if anyone knows of a way to
> get at the #define state of the C preprocessor so that such a thing
> could be done, I would greatly appreciate it :)
>
> In moments of desperation I have considered an automated brute
> force strategy enumerating all possible constant names of a given
> size, emitting a test program to printf the value, testing for successful
> compilation, and then adding that to a database of known values. Even
> if this took a dat to run it might be worthwhile in terms of saving
> developer heartache, given our need to build on multiple platforms with
> multiple bitness with multiple versions of dependencies.
>
> Please don't hesitate to propose even awkward solutions! Nothing
> could be worse than the brute-force plan. And even an awkward solution
> is probably better than the manual #define constant curation that we
> currently do.
"gcc -dM -E file.c" will write to stdout the current set of preprocessor
symbols, after preprocessing file.c and anything it #includes. The same
will work for clang, icc and (I think) the HP and portland group compiler.
Sun Studio (or whatever it's called, if it still exists) is "-xdumpmacros -E".
I've no idea if there's anything equivalent for visual studio.
Cheers,
Steve
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