Export to a Namespace?

Export to a Namespace?

[Jeremy T. Smith]

I'm supporting a large mass of legacy Ada and my boss wants to add new
functions using C++.  There are about 2000 constants defined in the Ada
code that we'll need visible to C++.  Not a problem, a quick Perl script
will add a pragma Export after each declaration.  The values being
exported are resolved at compile time, otherwise I'd just duplicat the
declarations in C++.

BUT, our system architect is a stickler about not polluting the global
namespace, so can I export from Ada to a C++ namespace?  Perhaps
something like (though this won't compile on my Green Hills compiler):

C++ Side:
namespace My_Wrapper {
   extern int First_Val;
   extern int Next_Val;
}

Ada Side:
   First_Val : constant integer := Some_Withed_In_Named_Number;
pragma Export(CPP, First_Val, "My_Wrapper::First_Val");
   Next_Val : constant integer := First_Val'Succ;
pragma Export(CPP, Next_Val, "My_Wrapper::Next_Val");

Any help would be much appreciated, even if it's just a "You can't do
that"!

Thanks

Jeremy

Re: Export to a Namespace?

[Pascal Obry]

"Jeremy T. Smith" <jeremy.t.smith2@boeing.com> writes:

> I'm supporting a large mass of legacy Ada and my boss wants to add new
> functions using C++.  

This is the problem, do not fix the code, fix your boss :)

Pascal.

-- 

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Re: Export to a Namespace?

[Stephen Leake]

"Jeremy T. Smith" <jeremy.t.smith2@boeing.com> writes:

> I'm supporting a large mass of legacy Ada and my boss wants to add new
> functions using C++.  There are about 2000 constants defined in the Ada
> code that we'll need visible to C++.  Not a problem, a quick Perl script
> will add a pragma Export after each declaration.  The values being
> exported are resolved at compile time, otherwise I'd just duplicat the
> declarations in C++.
> 
> BUT, our system architect is a stickler about not polluting the global
> namespace, so can I export from Ada to a C++ namespace?  Perhaps
> something like (though this won't compile on my Green Hills compiler):
> 
> C++ Side:
> namespace My_Wrapper {
>    extern int First_Val;
>    extern int Next_Val;
> }
> 
> Ada Side:
>    First_Val : constant integer := Some_Withed_In_Named_Number;
> pragma Export(CPP, First_Val, "My_Wrapper::First_Val");
>    Next_Val : constant integer := First_Val'Succ;
> pragma Export(CPP, Next_Val, "My_Wrapper::Next_Val");
> 
> Any help would be much appreciated, even if it's just a "You can't do
> that"!

Find out how the C++ compiler mangles the C++ name to the link name;
it may be something like My_Wrapper@Next_Val, but it's probably
worse. Then use the Link_Name parameter of Export to specify that link
name.

As Pascal said, it would be better to fix your boss!

-- 
-- Stephe

Re: Export to a Namespace?

[Matthew Heaney]

"Jeremy T. Smith" <jeremy.t.smith2@boeing.com> wrote in message
news:3D948F1F.9A87CE48@boeing.com...
>
> BUT, our system architect is a stickler about not polluting the global
> namespace, so can I export from Ada to a C++ namespace?  Perhaps
> something like (though this won't compile on my Green Hills compiler):
>
> C++ Side:
> namespace My_Wrapper {
>    extern int First_Val;
>    extern int Next_Val;
> }

The problem is you don't know how the compiler mangles names.

What I would do is use extern but with C linkage, e.g.

extern "C" {
extern int My_Wrapper_First_Val;
extern int My_Wrapper_Next_Val;
}

or something like that.

I'm not sure external linkage and C++ namespaces are really compatible.

If you really want to keep the namespace, you could try something like:

namespace My_Wrapper {
   int First_Val();
   int Next_Val();
}

inline int My_Wrapper::First_Val()
{
   return My_Wrapper_First_Val;
}

inline int My_Wrapper::Next_Val()
{
   return My_Wrapper_Next_Val;
}

or something like that.