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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Exporting generic's and tagged types
Date: 13 Apr 2001 07:13:07 +0100
Organization: CodeFella
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Date: 2001-04-13T06:13:07+00:00
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Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov> writes:

> You can put a "pragma Export (C, ...)" in the generic package
> itself, so that when it is instantiated, the appropriate things are
> exported.
> 
> Does that do what you want?
> 
> One problem with this scheme is the C name. If you specify it
> explicitly in the pragma Export, you cannot instantiate the package
> twice (you'll get link time collisions). On the other hand, if you
> do not specify it explicitly, you have a compiler dependency.

You can (in GNAT, anyway) supply a computed string for pragma Import:

  -- This string is used to prefix the C names of system calls in the
  -- imported C functions below. If empty, you get the actual system call
  -- (open(), etc); you can set it to "bp_" to access the corresponding
  -- versions in the file bp.c, which either report the call and pass it on
  -- to the real system interface or (if compiled with SIMULATE_DEVICE
  -- defined) provide a simple simulation.
  Import_Prefix : constant String := "";

....

    function Open (Path : Interfaces.C.Strings.Chars_Ptr;
                   Oflag : Interfaces.C.Unsigned) return Interfaces.C.Int;
    pragma Import (C, Open, Import_Prefix & "open");