Hello Amit,
On Mon, 1 Aug 2005 17:57:48 +0530 "Amit Dang"
<[EMAIL PROTECTED]> wrote:
> Hi Vadiraj,
> Thanks for the explaination but when i try following structure
> struct temp
> {
> char c; /* 1 byte lenght */
> int i; /* 4 byte length */
> char c1; /* 1 byte length */
> long long d /* 8 bytes lenght */
> };
> on a linux machine x86 32-bit with gcc 2.96. It gives its size = 20 bytes
> not 24 bytes (as explained by you)
See below (this applies to both members sorting examples from Vadiraj):
struct padded offset
member size size range
-------------------------------
c 1 4 0-3
i 4 4 4-7
c1 1 4 8-11
d 8 8 12-19
So, 20 bytes. Isn't it right?
Regards,
> ----- Original Message -----
> From: "Vadiraj" <[EMAIL PROTECTED]>
> To: "Amit Dang" <[EMAIL PROTECTED]>
> Sent: Monday, August 01, 2005 5:44 PM
> Subject: Re: Any pointer to Byte Alignment & Structure Padding?
>
>
> > On 8/1/05, Amit Dang <[EMAIL PROTECTED]> wrote:
> > > Hi,
> > > Can any body provide some light on Byte Alignment & Structure Padding
> > > for gcc linux x86 32-bit?
> >
> > The system expects the address of a variable to be multiple of
> > its size. Meaning for 32 bit x86 int being 4 bytes. The address
> > location of a int variable is expected to be at multiple of 4.
> > ex 0 4 8 12 16. if its double then its expected it to be multiple of 8.
> > 0 8 16 ...
> >
> > In case of structure allignment... this is achieved by padding.
> > if this is the structure
> > struct temp
> > {
> > char c; /* 1 byte lenght */
> > int i; /* 4 byte length */
> > char c1; /* 1 byte length */
> > long long d /* 8 bytes lenght */
> > };
> >
> > c starts at offset x( x is assured 4 byte alligned by gcc), i should
> > start at x+4 as it has to be multiple of 4 3 bytes of padding will be
> > done by gcc.
> > c1 starts at x+9, no padding is required char is 1 byte.
> > d starts at x+16,7 bytes of padding to get multiple of 8.
> >
> > It would differ if you re arrange the struct like this.
> > struct temp
> > {
> > char c; /* 1 byte lenght */
> > int i; /* 4 byte length */
> > long long d /* 8 bytes lenght */
> > char c1;
> > };
> >
> > for same base offset...i will be from x+4 d would start from x+8,
> > there would be no padding for d and c1 at x+16.
> >
> > I hope it helps.
> > --
> > cheers,
> > Vadi
>
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wwp
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