-- interfex.adb       use of interface packages

-- built using commands:
--    gcc -c interfex.adb
--    gcc -c a_funct2.ads  (not really needed here)
--    gcc -c a_funct2.adb
--    gcc -c c_funct2.c
--    gnatbl interfex.ali a_funct2.o c_funct2.o
--    interfex
-- The output is:
-- Interfex running
-- I am now in C_Funct 
-- An integer is passed 5 
-- A float is passed 7.3 
-- A string is passed What 
-- now calling a_funct2(I) 
-- In A_Funct2
-- a_funct2 got integer  5
-- now returning 4.73 
-- returned  4.73000000000000E+00

with Interfaces;
with Interfaces.C;
with Interfaces.C.Strings;
with Interfaces.C.Pointers;
with Text_IO;

procedure InterfEx is

   -- rename to keep code below neater
   subtype Chars_Ptr is Interfaces.C.Strings.Chars_Ptr;
   function New_String(S : String) return Chars_Ptr renames 
                      Interfaces.C.Strings.New_String;

   -- an Ada specification must correspond to C function prototype
   function C_Funct2(I : Integer; F : Float; S : Chars_Ptr) return Long_Float;

   -- the Ada compiler must know what language calling convention and Ada name 
   pragma Import (C, C_Funct2);

   -- optionally, 
   -- pragma Import ( Convention    => C,
   --                 Entity        => C_Funct2,
   --                 External_Name => "c_funct2",
   --                 Link_Name     => "_c_funct2");

   I : Integer := 5;
   F : Float   := 7.3;
   S : String(1..4) := "What";     -- normal Ada string
   D : Long_Float;

begin

   Text_IO.Put_Line("Interfex running");
   D := C_Funct2(I, F, New_String(S)); -- C function produces output
   Text_IO.Put_Line("returned " & Long_Float'Image(D));

end InterfEx;