H.11.2 Exporting Ada Entities

Building a DLL is a way to encapsulate a set of services usable from any application. As a result, the Ada entities exported by a DLL should be exported with the C or Stdcall calling conventions to avoid any Ada name mangling. As an example here is an Ada package API, spec and body, exporting two procedures, a function, and a variable:

     

     with Interfaces.C; use Interfaces;
     package API is
        Count : C.int := 0;
        function Factorial (Val : C.int) return C.int;
     
        procedure Initialize_API;
        procedure Finalize_API;
        --  Initialization & Finalization routines. More in the next section.
     private
        pragma Export (C, Initialize_API);
        pragma Export (C, Finalize_API);
        pragma Export (C, Count);
        pragma Export (C, Factorial);
     end API;
     

     

     package body API is
        function Factorial (Val : C.int) return C.int is
           Fact : C.int := 1;
        begin
           Count := Count + 1;
           for K in 1 .. Val loop
              Fact := Fact * K;
           end loop;
           return Fact;
        end Factorial;
     
        procedure Initialize_API is
           procedure Adainit;
           pragma Import (C, Adainit);
        begin
           Adainit;
        end Initialize_API;
     
        procedure Finalize_API is
           procedure Adafinal;
           pragma Import (C, Adafinal);
        begin
           Adafinal;
        end Finalize_API;
     end API;
     

If the Ada DLL you are building will only be used by Ada applications you do not have to export Ada entities with a C or Stdcall convention. As an example, the previous package could be written as follows:

     

     package API is
        Count : Integer := 0;
        function Factorial (Val : Integer) return Integer;
     
        procedure Initialize_API;
        procedure Finalize_API;
        --  Initialization and Finalization routines.
     end API;
     

     

     package body API is
        function Factorial (Val : Integer) return Integer is
           Fact : Integer := 1;
        begin
           Count := Count + 1;
           for K in 1 .. Val loop
              Fact := Fact * K;
           end loop;
           return Fact;
        end Factorial;
     
        ...
        --  The remainder of this package body is unchanged.
     end API;
     

Note that if you do not export the Ada entities with a C or Stdcall convention you will have to provide the mangled Ada names in the definition file of the Ada DLL (see Creating the Definition File).