Can you call C++ functions from Ada?

Question

Can you call C++ functions from Ada?

I'm wondering if there is a way to do this directly, without doing the implementation in C and writing a C++ wrapper & and Ada wrapper, e.g. I would like to go c++ -> Ada rather than c++ -> c -> Ada.

Answer 1

The problem with Ada to C++ is that C++ does NOT have a defined ABI.
Each compiler is allowed to define the most effecient ABI it can.

Thus interfacing from other languages (Ada) is a pain as you would need your Ada compiler to know which compiler the C++ was compiled with before it could generate the correct code to call any C++ method/function.

On the other hand the C ABI is well defined a standard across all compilers and as such provides a nice convenient interface for any language to connect with.

Answer 2

The only really compiler-agnostic answer I can give you is that it is just as possible as calling C++ from C on your system.

Much like with C, you have to figure out your C++ routine's name-mangled symbol and write a binding on the C (in this case the Ada) side that links to that mangled name. You will also probably have to do some things on the C++ side, like declaring the C++ function extern.

If you can declare your C++ function extern "C", it's easy. Just do that on the C++ side, and use Ada's standard C import features on the Ada side.

Example:

in your cpp:

extern "C" int cpp_func (int p1, int p2) {
   ; // Whatever..
}

in your .adb:

function cpp_func (p1, p2 : Interfaces.C.Int) return Interfaces.C.Int;
pragma Import (C, cpp_func); 

...
Result : constant Interfaces.C.Int := cpp_func (1, 2);

Answer 3

You might be interested in this paper, which discusses an object-level binding of Ada to C++:

http://www.adacore.com/uploads/technical-papers/Class_level_interfacing.pdf

Also, recent version of GNAT feature a powerful automatic binding generator.

Answer 4

It does not seem possible...

Information from here

"Direct interface to C++ from Ada is outside the scope of the Ada (at least 95)"

Answer 5

swig might be able to do it

Answer 6

I haven't touched Ada since 99/00 so my memory may be a bit sketchy but when we were working on a graphical windows app in Ada we needed to do some stuff in C++ (non mission critical) and the way we incorporated the two was to have the c++ stuff in a dll(s) and then create a C wrapper to that DLL and then use a pragma interface that specified the c wrapper and then we could call the methods within the dll from that interface.

I think it amounted to some triple maintenance because the method signatures had to be updated in the pragma interface and the C wrapper if they changed in the c++ dll.

Basically it was a pain. I think we had to use a Win32 Lean and Mean precomplier directive in the C wrapper.

Anyway, that is all the three of us who worked on the project can remember.

Answer 7

Green Hills Software published a great PDF about this as well.
http://www.ghs.com/download/whitepapers/ada_c++.pdf