From:	"J.R. Wessels" <wessels AT megavision DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Struct optimizing by compiler
Date:	Sat, 18 Apr 1998 10:51:28 -0600
Organization:	Kimball High School
Lines:	34
Message-ID:	<3538DA10.124F11CB@megavision.com>
References:	<01bd6ad8$16320920$151601bf AT cb001687>
NNTP-Posting-Host:	kim02.megavision.com
Mime-Version:	1.0
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp

I think that the compiler allocates four bytes for X because of alignment.  If
you organize the structure to declare the largest members first and smallest
last, it should fix your problem.  Another source of your problem may be that
the default alignment is set at 4 bytes.

Jasper van Woudenberg wrote:

> Hi,
>
> When i try to define a structure, it seems that the compiler sometimes
> optimizes the variables to start at a 'long' address. for example:
>
> struct X { short X,            // (can) reserve 4 bytes for X, to get Y at
> a 'long' address
>            long  Y,
>            short Z };
>
> Sometimes interrupt routines return pointers to data structures in memory,
> and when i copy that data into a structure like the above, the data is
> corrupted, because X uses 4 bytes in stead of 2 bytes. How can i make the
> compiler _always_ reserve 2 bytes for a short, 4 bytes for a long, etc.?
>
> Jasper.



--

J.R. Wessels

wessels AT megavision DOT com
http://www.geocities.com/SiliconValley/Horizon/7865

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