Re: Importing C structs?

[mheaney@on2.com (Matthew Heaney)]

Freejack <freejack@nospam.net> wrote in message news:<pan.2003.07.31.07.52.36.94842.845@nospam.net>...
> On Thu, 31 Jul 2003 01:35:57 -0400, Matthew Heaney wrote:
> 
> > The type DBTYPE is a bit of a mystery at this point, since structs
> > aren't typically passed by value in C.  Perhaps DBTYPE is really a
> > pointer?
> 
> The header file declares it thusly....
> 
> /*******************************************************
>  * Access methods.
>  *******************************************************/
> /*
>  * !!!
>  * Changes here must be reflected in java/src/com/sleepycat/db/Db.java.
>  */
> 	typedef enum {
> 	DB_BTREE=1,
> 	DB_HASH,
> 	DB_RECNO,
> 	DB_QUEUE,
> 	DB_UNKNOWN			/* Figure it out on open. */
> 	} DBTYPE;
>  
> So I'm assuming I could just use an Ada enumerated type. (It compiles when I
> do this, but it fails at runtime.)

You'll need to use a rep clause to specify that the enumeration
literals start with value 1.  You'll also need to specify convention C
for the enumeration type.

type DBTYPE is (DB_BTREE, DB_HASH, ...);
pragma Convention (C, DBTYPE);
for DBTYPE use (DB_TYPE => 1);  --need others?

Alternatively, you could just use a C int type:

type DBTYPE is new C.int;

DB_BTREE : constant DBTYPE := 1;
DB_HASH : constant DBTYPE := 2;
etc

Sometimes using an integer type to map to a C enum type is the better
choice.


> The second hurdle I'll need to jump is creating a suitable Ada
> replacement for this buttload of defines that occur after the DBTYPE
> declaration.
> 
> /*
>  * DB access method and cursor operation values.  Each value is an operation
>  * code to which additional bit flags are added.
>  */
> #define	DB_AFTER	 1		/* c_put() */
> #define	DB_APPEND	 2		/* put() */
> #define	DB_BEFORE	 3		/* c_put() */

Just use named numbers:

DB_AFTER : constant := 1;
DB_APPEND : constant := 2;
DB_BEFORE : constant := 3;
etc