Re: How to import C pointers to structures?

["björn lundin" <b.f.lundin@gmail.com>]

Den tisdagen den 20:e maj 2014 kl. 00:26:07 UTC+2 skrev Victor Porton:
 
> Suppose we have a C function:
> void f(struct_t *ptr);
> How to import it to Ada? We don't know struct_t layout.

I used a binding to Postgresql that I found a long time ago,
(by Samuel Tardieu), that declares this:

   type Pg_Conn is null record;
   type Pg_Conn_Access is access Pg_Conn;
   pragma Convention (C, Pg_Conn_Access);

   type Pg_Result is null record;
   type Pg_Result_Access is access Pg_Result;
   pragma Convention (C, Pg_Result_Access);


To get a pointer to the db_connection object you use

   function PQ_Connectdb (Conn_Info : Chars_Ptr) return Pg_Conn_Access;
   pragma Import (C, PQ_Connectdb, "PQconnectdb");
   

and then use it to get result sets
   function Pq_Exec (Conn  : Pg_Conn_Access;
                     Query : Chars_Ptr)
                     return Pg_Result_Access;
   pragma Import (C, Pq_Exec, "PQexec");


So, you do not need to know the underlaying structure,
only to pass the pointer around.


-- 
Björn Lundin