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Date: 1 Oct 92 14:23:09 GMT
From: convex!rtorres@uunet.uu.net  (Randy Torres)
Subject: Variant Records from Ada to C
Message-ID: <rtorres.717949389@mikey>
List-Id: <comp.lang.ada>

Would the following be safe.  I have a variant record and want to pass
it to a C routine.  I currently know what the data structures will look
like when past to C.  However, will this data structure change with
releases of Ada compilers, as well as different compilers?


with system;

procedure a is
   procedure pass_string_array( str : system.address);
   pragma interface(c, pass_string_array);
   procedure pass_record( rec : system.address);
   pragma interface(c, pass_record);
   type xrec (p1 : integer; p2: integer) is
   record
      b  : integer;
      s1 : string(1..p1);
      c  : integer;
      s2 : string(1..p2);
      case p1 is
         when 7 =>
            fld1 : integer;
         when others =>
            fld2 : integer;
      end case;
   end record;
   myrec : xrec(7,8);
begin
   myrec.b := 66;
   myrec.c := 77;
   myrec.s1 := "AAAAABB";
   myrec.s2 := "CCCCCDDD";
   myrec.fld1 := 88;
   pass_string_array(myrec.s1'address);
   pass_string_array(myrec.s2'address);
   pass_record(myrec'address);
end;




C file.



#include <stdio.h>
   typedef struct xrec {      
      int p1;
      int p2;
      int b;
      unsigned s1_offset;
      struct {
         int element_size;    /* s1(1)'size */
         int lower;           /* s1'first */
         int upper;           /* s1'last */
         int total;           /* s1'size */
      } dv1;
      int c;
      unsigned s2_offset;
      struct {
         int element_size;    /* s2(1)'size */
         int lower;           /* s2'first */
         int upper;           /* s2'last */
         int total;           /* s2'size */
      } dv2;
      union {
         int fld1;
         int fld2;
      } n;
   } *xrec_t;

void pass_record(xrec_t my)
{
   char *s1, *s2;
   s1 = (char *)&(my->s1_offset);
   s1 += my->s1_offset;
   s2 = (char *)&(my->s2_offset);
   s2 += my->s2_offset;
   printf("p1 = %d\n",my->p1);
   printf("p2 = %d\n",my->p2);
   printf("b = %d\n",my->b);
   printf("c = %d\n",my->c);
   printf("fld1 = %d\n", my->n.fld1);
   printf("s1 = %s\n",s1);   
   printf("s2 = %s\n",s2);   
}

void pass_string_array(char *s)
{
   printf("s = %s\n",s);   
}




Sharon Shaw			
CONVEX Systems Integration and Support