Re: Thick bindings to a C library and gnattest: suggestions?

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

On 07/02/2013 01:33 AM, Maurizio Tomasi wrote:
>     type Vector is array (Positive range <>) of aliased Natural;
>
>     type Pointer is access all Natural;
>     pragma Convention (C, Pointer);
>
>     procedure Read_Vector_From_File (A : out Vector) is
>
>        procedure Internal (A : Pointer; N : Interfaces.C.unsigned);
>        pragma Import (C, Internal, "read_vector");
>
>     begin
>        Internal (A (A'First)'Access, A'Length);
>     end Read_Vector_From_File;

There is no need for access types in Ada to do this. See ARM B.3 (70):

"An Ada parameter of an access-to-subprogram type is passed as a pointer to a C 
function whose prototype corresponds to the designated subprogram's specification."

In other words, you can write

type Vector is array (Positive range <>) of Natural;

procedure Read_Vector_From_File (A : out Vector) is
    procedure Internal (A : out Vector; N : in Interfaces.C.Unsigned);
    pragma Import (C, Internal, "read_vector");
begin -- Read_Vector_From_File
    Internal (A => A, N => A'Length);
end Read_Vector_From_File;

and the compiler takes care of passing a C pointer to the 1st component of A. No 
need for the components of Vector to be aliased, and no problems with 
accessibility checks.

-- 
Jeff Carter
"That was the most fun I've ever had without laughing."
Annie Hall
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