Re: Why doesn't an access to an imported C function work?

Re: Why doesn't an access to an imported C function work?

[Robert Dewar]

An access to subprogram value cannot point to subprograms with an
incompatible convention. The diagnostic from GNAT is:

    25.    Random := Random_Gaussian'Access;
                     |
        >>> subprogram has invalid convention for context

You need to use pragma Convention to specify the appropriate convention.

Why doesn't an access to an imported C function work?

[Matthew Kennedy]

Hello, 

My appended sample program refuses to compile at the line where

  Random := Random_Gaussian'Access;

Where Random_Gaussian is a C function to be imported into Ada. I was
wondering wether Ada supported access to imported C functions (I know it
supports access to Ada function types) at all? 

It is important that the original C-source cannot be modified.

------------------------------------------------------------
with Ada.Float_Text_Io, Ada.Numerics, Text_Io, Interfaces.C;
use  Ada.Float_Text_Io, Ada.Numerics, Text_Io, Interfaces.C;

procedure Function_Access is

   function Random_Gaussian(X : in Double) return Double;
   function Random_Uniform(X : in Double) return Double;

   pragma Import(C, Random_Gaussian, "RandomGaussian");
   pragma Import(C, Random_Uniform, "RandomUniform");

   type Function_Access is access function (X: in Double ) return
Double;

   Random : Function_Access;

   procedure Evaluate(F : Function_Access; X : in Double; Y : out
Double) is
   begin
      Y := F(X);
   end Evaluate;

   X, Y : Double;

begin

   Random := Random_Gaussian'Access;

   X := 1.0;
   Y := Random(X);

--   Evaluate(F'Access, X, Y);
   Put(Item => X); New_Line;
   Put(Item => Y); New_Line;

end Function_Access;


-- 
Matthew Kennedy
Student of Electrical & Electronics Engineering
University of Southern Queensland, Australia