Re: C++ to Ada Link Problems

["Stanley R. Allen" <s_allen@hso.link.com>]

James Huckaby wrote:
> 
> 
> Simply put, is it at all possible with the resources I have now
> (Sun Ada 2.1 and Sun C++ 3.0, upgrading soon to Sun Ada 3.0, and
> Sun C++ 4.0) to link Ada and C++?

"Linking C++ and Ada" is an umbrella topic.  You might mean
by this that you need to "interface" Ada and C++.  If so, you
may need to set up some C code which calls the C++ code,
and interface the Ada to this using pragma Interface.

But by the wording of your question, I suppose that you
have alreasy worked out those issues and are trying now
to build an executable.  The main issue is C++ constructor/
deconstructor ("Xtor") operations for statically-declared
object instances: how do they get called?  In Ada, global
variable initialization is defined in the language as
part of the elaboration process.  In C++, it is the
job of external tools.  A common way of creating the
contructor/destructor caller is to "munch" the object
code produced by the C++ compiler (using a munching
tool), which will produce a C file that calls the
Xtors.  Compiling this C file and linking the new
object module with the C++ code will ensure that the
C++ static objects are constructed properly.  To link
with Ada, ensure that the object file created from
the C program is included as one of the inputs to the
linker building the Ada main.  (Since you are talking
about Ada 83, I assume that the main program is in Ada.)
My understanding is that munching is the approach
used by the GNU C++ implementation.

Other C++ compilers don't require a separate munching
phase, but expect that the linker will include calls
to the proper contructor/destructors.  If the Ada
binding program (I think that would be a.ld for SunAda)
is used to create the Unix "ld" command, then the
stuff C++ needs will not be included.  I'm not sure how
it works on the Sun; on the SGI with Delta C++ you can
specify that the C++ compiler itself ("CC") be used as
the linker.  This will include the necessary code to
call the Xtor operations for static C++ objects.

Disclaimer: I have only done the above with GNAT, but
I believe the same principles apply when linking code
produced by other Ada compilers.  

-- 
Stanley Allen
mailto:s_allen@hso.link.com