Calling Ada from C++ (MS Visual C++)

Calling Ada from C++ (MS Visual C++)

[Julian Robbins]

Hi All,

I have a question regarding calling Ada from Microsoft Visual C++. I
am currently in the situation where I can export a function from an
Ada package and then compile this into my C++ application, following
the standard approach of pragma Export. For example, I have the
spec/code as follows:

     package MathUtil is
        function Square( Value : in Float) return Float ;
        pragma export (CPP, Square, "ada_square") ;
     end MathUtil;

     package body MathUtil is
        function Square( Value : in Float) return Float is
        begin
           return Value * Value ;
        end Square;
     end MathUtil ;

I can use gcc command (GNAT 3.14) to compile this into a .o file,
include this in my Visual C++ project and then simply call the
"ada_square" function from anywhere in my C++ code. This works and
produces an executable that does what it is supposed to.

However, this is a very simplistic model. I have done much reading on
the subject of interfacing Ada and C++ and I believe that the above
approach would fall over as soon as I started to put any real code in
the Ada section. Specifically I am talking about the Ada executive
functions and "ellaboration". The C++ program is the 'main' program
and so no Ada 'main' is yet being called. Could some please comment on
whether my assertion is correct? If I only include the .o files, at
some point it is going to fall over horribly?

So, using GNAT I believe that I can include the 'adainit()' and
'adafinal()' in the binding stage using 'gnatbind -n mathutil.ali'.
However, this seems to produce a .o file that I could then only use
with gnatlink to link the C++ objects and Ada objects together. This I
can not do - I need to use MS Visual Studio to link the final
executable, including any relevant Ada objects.

My big question, therefore, is : Is this possible? Can I use the GNAT
tools to create the adainit() and adafinal() functions in such a way
that I can then simply include the object files into my Visual Studio
project?

Thanks in advance for any help!

Julian Robbins
Software Engineer
Logica UK

Calling Ada from C++ (MS Visual C++)

[Caldwell Ian]

You can use a DLL. Have a look at 'Microsoft Windows Topics' section in the gnat user guide.

Ian Caldwell
Q218 
QinetiQ Malvern 
+ 44 (0) 1684 89 4461


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Re: Calling Ada from C++ (MS Visual C++)

[Stephen Leake]

julian_robbins@bigfoot.com (Julian Robbins) writes:

> So, using GNAT I believe that I can include the 'adainit()' and
> 'adafinal()' in the binding stage using 'gnatbind -n mathutil.ali'.
> However, this seems to produce a .o file that I could then only use
> with gnatlink to link the C++ objects and Ada objects together. This I
> can not do - I need to use MS Visual Studio to link the final
> executable, including any relevant Ada objects.

You can link the .o file containing adafinal() and adainit() with your
C++ code, same as any other Ada .o.

-- 
-- Stephe

Re: Calling Ada from C++ (MS Visual C++)

[Julian Robbins]

Okay, so here is what I have done...

Compiled the original "mathutil.adb" into "mathutil.o". Then used
"gnatbind -n mathutil" which produced the files "b~mathutil.adb" and
".ads". I then compiled these using gcc and renamed the resulting .o
file "main.o".

Within my VC++ project I have then included the mathutil.o and main.o
files, added calls to adainit() and adafinal() and then
compiled/linked. This throws up various missing links, so I have
included the following library files:
   libgnat.a
   libgcc.a
   libmingw32.a

Does this seem correct?? It seems to compile and run, but I can't help
thinking that this process seems a bit odd.

Cheers,

Julian



Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov> wrote in message news:<u1yduhuw5.fsf@gsfc.nasa.gov>...
> julian_robbins@bigfoot.com (Julian Robbins) writes:
> 
> > So, using GNAT I believe that I can include the 'adainit()' and
> > 'adafinal()' in the binding stage using 'gnatbind -n mathutil.ali'.
> > However, this seems to produce a .o file that I could then only use
> > with gnatlink to link the C++ objects and Ada objects together. This I
> > can not do - I need to use MS Visual Studio to link the final
> > executable, including any relevant Ada objects.
> 
> You can link the .o file containing adafinal() and adainit() with your
> C++ code, same as any other Ada .o.

Re: Calling Ada from C++ (MS Visual C++)

[Stephen Leake]

julian_robbins@bigfoot.com (Julian Robbins) writes:

> Okay, so here is what I have done...
> 
> Compiled the original "mathutil.adb" into "mathutil.o". Then used
> "gnatbind -n mathutil" which produced the files "b~mathutil.adb" and
> ".ads". I then compiled these using gcc and renamed the resulting .o
> file "main.o".

I wouldn't call it "main", since it is _not_ your C "main". Call it
"ada_elab_stuff". Or at least "ada_main". Actually, there's nothing
wrong with "b~mathutil" :).

> Within my VC++ project I have then included the mathutil.o and
> main.o files, added calls to adainit() and adafinal() and then
> compiled/linked. This throws up various missing links, so I have
> included the following library files: libgnat.a libgcc.a
> libmingw32.a
> 
> Does this seem correct?? 

Yes, you've got it.

> It seems to compile and run, but I can't help thinking that this
> process seems a bit odd.

Welcome to the world of multi-language multi-vendor programming :).

You've got it easier than I did; I was using Borland C++, which has a
different object file format than GNAT on Win32. So I had GNAT build a
DLL to link with Borland. Reverse engineering the naming conventions
took a while!

Just out of curiosity, why are you using MS C++ instead of Gnu C++?
I'll assume it's to get MFC.

-- 
-- Stephe

Re: Calling Ada from C++ (MS Visual C++)

[Karel Miklav]

> Just out of curiosity, why are you using MS C++ instead of Gnu C++?
> I'll assume it's to get MFC.

I'm considering options to escape from MS world (VC++/VB/scripting/COM/),
mostly get rid of VC. Is it possible to use Gnu C++ on Windows box as an
industry-strenght compiler with possibilities to interface to other
languages like Ada and Eiffel without too much hassle (hassle = 90% of time
spent on interfacing)?

Regards,
Karel Miklav

Re: Calling Ada from C++ (MS Visual C++)

[Stephen Leake]

"Karel Miklav" <karel@inetis.removeme.com> writes:

> > Just out of curiosity, why are you using MS C++ instead of Gnu C++?
> > I'll assume it's to get MFC.
> 
> I'm considering options to escape from MS world (VC++/VB/scripting/COM/),
> mostly get rid of VC. Is it possible to use Gnu C++ on Windows box as an
> industry-strenght compiler with possibilities to interface to other
> languages like Ada and Eiffel without too much hassle (hassle = 90% of time
> spent on interfacing)?

Interfacing Gnu Ada and Gnu C++ is easier than interfacing Gnu Ada and
non-Gnu C++. Neither is standard; the simplest way is to use C as the
intermediate language. But Gnu Ada does support directly
importing/exporting Gnu C++ classes. 

I'm not clear on Eiffel; if it supports exporting functions to Gnu C,
then interfacing it with Gnu Ada will be simple.

"industry-strength" is a very ambiguous term. If you mean "supported
by a strong company with a good rep", then Gnu Ada is
industry-strength. If you mean "comes with lots of widgets that do 90%
of my business GUI app", then no, Gnu Ada is not.

The amount of "hassle" involved in interfacing depends heavily on what
libraries you are interfacing to. 

-- 
-- Stephe