Question

I have a C++ structure in "MyData.h"

struct MyData
{
    int a;
    int b;
};

That I want to pass a pointer of it into an Ada call

#include "MyData.h"
extern "C" void ada_call(MyData* data);

void func()
{
    MyData* data = new MyData();
    ada_call(data);
}

How can I build an Ada function that will accept this?

Answer 1

The solution has a couple steps to it.

You need to generate an Ada record for that struct. g++ has a built in tool for doing this. Run:

g++ -c -fdump-ada-spec "MyData.h" -C

And you will get a mydata_h.ads which has a definition of a record that matches your struct. It should look like this:

with Interfaces.C; use Interfaces.C;

package MyData_h is

   type MyData is record
      a : aliased int;  -- MyData.h:3
      b : aliased int;  -- MyData.h:4
   end record;
   pragma Convention (C_Pass_By_Copy, MyData);  -- MyData.h:1

end MyData_h;

Once you have that, you need to write a procedure that takes it as a parameter. This procedure must have it passed as 'access', it must then be exported, so it is accessible from C.

data_function.ads:

with MyData_h;
use MyData_h;

package DATA_FUNCTION is
    procedure ADA_CALL ( DATA : access MyData_h.MyData );
    pragma Export(Convention=>C,Entity=>ADA_CALL,External_Name=>"ada_call");
end DataFunction;

data_function.adb

with MyData_h;
use MyData_h;
with Interfaces.C; use Interfaces.C;

package body DATA_FUNCTION is

    procedure ADA_CALL ( DATA : access MyData_h.MyData )
    begin
        DATA.a = 1;
        DATA.b = 2;
    end ADA_CALL;
end DATA_FUNCTION;

Pass a pointer to a C++ struct into Ada

1 个答案: