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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Design help
References: <mailman.116.1173480208.18371.comp.lang.ada@ada-france.org>
Date: Sat, 10 Mar 2007 14:38:05 +0100
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Date: 2007-03-10T14:38:05+01:00
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Andrew Carrol writes:
> I am trying to design (what I guess is) a database table adapter.  Yes,
> it is a master's course assignment.  The current design is to use a file
> and have one record per line.  My goal is to get each line to be
> "serialized" so I can read the whole line in bytes and then take chunks
> of it and "cast" those into objects.

The answer depends on whether or not your file contains fixed-width
records.  If that is the case, I would simply declare a record type
and use Sequential_IO for the record type directly, like e.g.

type Seconds_Since_Epoch is new Ada.Interfaces.Unsigned_32;

type DB_Record is record
   Primary_Key   : Ada.Interfaces.Unsigned_32;
   Name          : String (1 .. 20);
   Address       : String (1 .. 100);
   Date_Of_Birth : Seconds_Since_Epoch;
end record;

package DB_Record_IO is
   new Ada.Sequential_IO (Element_Type => DB_Record);

But if, on the other hand, the file contains variable-width records,
such as comma-separated values (CSV), you will need more sophisticated
conversion functions.  In that case, I would use Ada.Streams.Stream_IO
directly and convert the Stream_Elements one by one.

If you want to convert to objects of tagged types, you should provide
a constructor function for your tagged type, like so:

type T is tagged record ... end record;

function To_T (Raw_Bytes : in Ada.Streams.Stream_Element_Array)
   return T;

HTH

Note that the database file will probably not contain the tag itself.
OTOH, if it does, then you can just use streams.

-- 
Ludovic Brenta.