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NNTP-Posting-Date: Thu, 27 Jan 2005 11:59:15 -0600
From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: Making ada (types) "visable" in C
References: <6acda821.0501270510.1dbfe551@posting.google.com>
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Date: Thu, 27 Jan 2005 11:59:15 -0600
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Xref: g2news1.google.com comp.lang.ada:8017
Date: 2005-01-27T11:59:15-06:00
List-Id: <comp.lang.ada>

>  type State_Buff is (Ok, Failed);
>
>  type Baud_Type is (R9600, R19200);
>
>  type Parity_Type is (None, Odd, Even);
>
>  type Stop_Bit_Type is (One, Two);

  Ada deals with things at the logical level, eg, a State_Buf object
either has the value Ok or the value Failed.  C deals with bit patterns,
and different C compilers running on different OSes or hardware use
different bit patterns.  Ada provides a way, "representation clauses",
to make the compiler use specific bit patterns for its logical types.
So, assuming that for your specific application the C bit pattern
for a State_Buf object is 32 bits with a value of 0 or 0xFFFFFFFF, you
would say
   type State_Buff is (Ok, Failed);
   for State_Buff use (Ok => 0, Failed => 16#FFFFFFFF#);
   for State_Buff'size use 32;
Similarly for the other types.