From: Matthew Bloch <mattbee@soup-kitchen.net>
To: Andrew Lees <andrewl@acay.com.au>
Cc: gcc-help@gcc.gnu.org
Subject: Re: struct packing reliability?
Date: Wed, 27 Feb 2002 04:18:00 -0000 [thread overview]
Message-ID: <20020227114216.3028.qmail@stoneboat.bytemark.co.uk> (raw)
In-Reply-To: <20020227023530.31397.qmail@stoneboat.bytemark.co.uk>
On Wednesday 27 February 2002 4:19 am, Andrew Lees wrote:
> Hi,
>
> I'm not sure this will help, but have you tried
>
> #pragma pack(1)
Yes, same results as when I use the __attribute__ qualifier.
Unless there's something I'm missing, I think it's impossible to pack
structs-within-structs on bit boundaries, as this test case demonstrates:
------------------------------------------------------------------------
#pragma pack(1)
struct test1
{
int a : 5;
struct {
int b1 : 3;
int b2 : 2;
} b;
int c : 5;
int d : 1;
};
struct test2
{
int a : 5;
int b : 5;
int c : 5;
int d : 1;
};
int main(void)
{
printf("%d %d\n", sizeof(struct test1), sizeof(struct test2));
/* prints '3 2', annoyingly */
}
#pragma pack()
------------------------------------------------------------------------
The non-portability aspect isn't a major concern for me, given that this is
for a fixed hardware platform and fixed compiler, but it's a shame that I
can't get the behaviour I'm after because it makes use of these structures
that little bit uglier.
Unless anybody knows better...?
--
Matthew > http://www.soup-kitchen.net/
> ICQ 19482073
next prev parent reply other threads:[~2002-02-27 11:36 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-02-26 18:38 Matthew Bloch
2002-02-27 4:18 ` Matthew Bloch [this message]
2002-02-28 15:55 ` Andrew Lees
2002-02-28 15:55 ` Andrew Lees
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