Rational Apex Ada - Pragma interface with C++

[John Smith]

Does anyone know how to use pragma interface for interfacing C++ functions
to an Ada program. I know how to do it with C, but can't seem to get it to
work with C++.

Thanks..

[Stephen Leake]

"John Smith" <som...@microsoft.com> writes:

The Ada 95 standard does not define how to interface with C++.

Your compiler may define this on its own; you'll have to consult the
compiler docs.

--
-- Stephe

[Matthew Heaney]

"John Smith" <som...@microsoft.com> wrote in message
news:H3s05...@news.boeing.com...

Interfacing with C++ requires care, especially if you have static variables
the require elaboration-time initialization.

When a C++ program loads, all the statics get initialized. There will be
some code inserted by the compiler to go this, just prior to call the C++
main.

The same is true of an Ada program.

In general, a C++ program will need a C++ main, and an Ada program will need
an Ada main.

If you don't have any statics, you may OK.

There's no official function you can call from an Ada program to perform the
C++ initialization -- you'll have to check your compiler docs.

There are official functions to perform Ada initialization -- there are two
linker symbols called "adainit" and "adafinal". If you have a C++ main, and
you're calling code written in Ada, then you'll need to call these.

In any event, there's no pragma to interface with C++ directly. I know GNAT
has compiler-specific pragmas to do this.

However, I wouldn't bother. Just create a C wrapper, and link to those.
For example, if you have a C++ class you want to use from Ada, like this:

class C
{
public:
void f();
//...
};

Assuming you don't mind manipulating a pointer, you can do this:

extern "C" C* makeC()
{
return new C;
}

extern "C" void freeC(C* p)
{
delete p;
}

extern "C" void c_f(C* p)
{
p->f();
}

On the Ada side, create a set of bindings for each of the external functions
above, e.g.

function Make_C return System.Address;
pragma Interface (C, Make_C);

procedure Free_C (Object : System.Address);
pragma Interface (C, Free_C);

procedure C_F (Object : System.Address);
pragma Interface (C, C_F);

You could add more type safety than I've shown above, e.g.

package C_Types is

type C_Type (<>) is limited private;

type C_Access is access all C_Type;
pragma Convention (C, C_Access);

function New_C return C_Access;

procedure Free (C : in out C_Access);

procedure Do_F (C : access C_Type);

private

type C_Type is null record;

function Make_C return C_Access;
pragma Interface (C, Make_C);

--etc
end C_Types;

[Marc A. Criley]

There are detailed instructions in the Apex documentation on how to do
this,
and they do work.

The part that isn't mentioned, though, is that the C++ _must_ be
compiled
with Apex C++. Otherwise the run-time environments conflict, and the
resulting executable runs unreliably, if at all, which was our
experience.
This rather significant restriction was stated by a Rational
representative.

Originally, the C++ code we had to link in was compiled with Sun's Forte
C++, and we were fortunate that the nature of the code was highly
algorithmic and portable, so compiling it with Apex C++ went quite
smoothly.

Marc A. Criley
Quadrus Corporation
www.quadruscorp.com

[John Smith]

Thank you for your input. Unfortunately I don't have the Apex C++ compiler
installed. Thanks.

"Marc A. Criley" <mc...@earthlink.net> wrote in message
news:3DA6B3DA...@earthlink.net...

[John Smith]

Thank you. I will give this a try.

John Smith
"Matthew Heaney" <mhe...@on2.com> wrote in message
news:uqbtbu...@corp.supernews.com...

[John Smith]

Hello Matthew,

I just tried your suggestion, but I don't quite know how to link it. I
compiled the C++ module that contains the externs with the CC compiler from
Sun OS and compiled the C code that interfaces with the C++ module with cc.
Now my problem is how do I link both together? I've generated two object
files, but then I'm stuck. Help please.

John

"Matthew Heaney" <mhe...@on2.com> wrote in message
news:uqbtbu...@corp.supernews.com...
>

[Jeffrey Creem]

Look for the view switch "NON_ADA_LINKAGE:"
Add the .o files from the c compile to this switch.

"John Smith" <som...@microsoft.com> wrote in message

news:H3zuq...@news.boeing.com...

[John Smith]

It doesn't seem to like that idea. It's complaining about the C++ obect
file.

"Jeffrey Creem" <je...@thecreems.com> wrote in message
news:Z3Jq9.48415$oq6.12550@sccrnsc01...

[Ted Dennison]

"John Smith" <som...@microsoft.com> wrote in message news:<H400I...@news.boeing.com>...

> It doesn't seem to like that idea. It's complaining about the C++ obect
> file.

Smart compiler. :-)