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From: Christopher Broeg <broeg@astro.uni-jena.de~>
Newsgroups: comp.lang.ada
Subject: Re: trying to call HDF5 from ada -- problems with constants
Date: Thu, 26 Aug 2004 13:46:12 +0200
Organization: Friedrich Schiller University Jena, Germany
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Date: 2004-08-26T11:46:12+00:00
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Jeff C, wrote:
> "Christopher Broeg" <broeg@astro.uni-jena.de~> wrote in message 
> news:cgk5i0$cfu$1@fsuj29.rz.uni-jena.de...
> 
>>What is the standard way to import C constants that are not "constant" 
>>from one run to the next, but derived from some "invisible" library in the 
>>.h files?
> 
> 
> 
> If they really vary from one run to the next then I think you have no choice 
> but to build bindings to C functions that return them. Alternatively 
> assuming you have enough of the source you could recreate the code that 
> builds
> the constants via macros from C code.
> 
> 
> If the constants vary from platform to platform but not run-to-run you can 
> use an approach like AdaSockets does
> where it builds the ada spec on the fly during the configure step using 
> constants.sh and constants.c
> (see the Adasockets distribution)
> http://www.rfc1149.net/devel/adasockets 
> 
> 

tx. I just realized that with gnat I can import the constants directly. 
I realized that the ada specifications in the RM do never explicitly 
mention functions or procedures with respect to pragma import. So I did:

    H5T_STD_I32BE_g : Hid_t;
    pragma Import(C,H5T_STD_I32BE_g , "H5T_STD_I32BE_g");

and it works! All you have to do is call H5open manually, which is done 
automatically with the c preprocessor. Is this behaviour 
compiler-dependant, or ADA standard?

I'm surprised, because there was this long thread on this very topic 
explicitly stating that ada cannot import c constants... But I guess it 
only referred to preprocessor constants. All "variing" constants are of 
course real c constants visible in the library.

Thanx a lot for the reply.

Chris