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From: Alfred Hilscher <Alfred.Hilscher@icn.siemens.de>
Newsgroups: comp.lang.ada
Subject: Re: Size and pack
Date: Wed, 10 Oct 2001 10:59:30 +0200
Organization: Siemens AG
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Date: 2001-10-10T10:59:30+02:00
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I'm not sure, but I think it is because Log_Num would start on an odd
adress otherwise, and so there are three bytes left  to align it to a
word boundary. Yes, shou should be able to do it with rep-spec.

Adrian Hoe wrote:
> 
> Hello,
> 
> I have the following declaration:
> 
>    type Rx_Header_Data is
>       record
>          Start_Byte   : Character := Latin_1.STX;
>          Splitter     : Character;
>          Command_Byte : Character;
>          Pad_Byte_1   : Character;
>          Pad_Byte_2   : Character;
>          Log_Num      : Interfaces.C.Long;
>          End_Byte     : Character := Latin_1.ETX;
>          LRC          : Character;
>       end record;
> 
> It supposed to be 11 bytes long but Rx_Header_Data'Size reports 14
> bytes. 'Size will report 11 bytes when I add the following line:
> 
> pragma pack (Rx_Header_Data);
> 
> I have found that Log_Num : Interfaces.C.Long takes up 7 bytes without
> pragma pack.
> 
> Why this happens? Can I use representation clause instead of pragma
> pack? If both methods work, which is the best approach and why?
> 
> I use GNAT 3.13p on Linux.
> 
> Thank you.