padding based on the bit interleaving(low order) which is basically hardware
dependent.

On Fri, Jul 29, 2011 at 10:10 PM, Puneet Gautam <puneet.nsi...@gmail.com>wrote:

> Thanks guys...so much...!!
>
> On 7/29/11, nullpointer <nullpointer...@gmail.com> wrote:
> > #include<stdio.h>
> > #include<conio.h>
> > struc MyStructA {
> >
> >  char a;
> >  char b;
> >  int c;
> > };
> >
> > struct MyStructB {
> >  char a;
> >  int c;
> >  char b;
> > };
> >
> > int main(void) {
> >
> >  struct MyStructA A;
> >  struct MyStructB B;
> >
> > int sizeA = sizeof(struct MyStructA);
> >  int sizeB = sizeof(struct MyStructB);
> >  return 0;
> >
> > }
> >
> > OUTPUT IS
> > A = 8
> > B = 12
> > Structure padding is done to try and make sure that variables start in
> > memory at addresses that are a multiple of their size.
> > This is more efficient at hardware level (needs less cpu ticks to read
> > or write variables) and in some platforms this is mandatory, though
> > not on i386. There are CPU's that can only handle double precision
> > floats if they are aligned on addresses that are a multiople of 8.
> >
> >
> > In this struct:
> > struct MyStructA {
> >
> >  char a;
> >  char b;
> > int c;
> > };
> > the beginning of the struct is to be assumed at 0 (I'l explain later)
> > a is 1 byte so it needs no padding in front of it.
> > the same goes for b.
> > but c is 4 bytes. it should be placed at an address boundary that is a
> > multiple of 4, so the compiler adds 2 dummy bytes in front of it.
> > These 2 bytes change the size from 6 to 8.
> > Now in this struct:
> > struct MyStructB {
> >  char a;
> >  int c;
> >  char b;
> > };
> >
> > a starts on 0, so no need for padding.
> > c needs 3 bytes in front of it, and b needs no padding.
> > this would bring the struct size to 9. HOWEVER, suppose that you place
> > 2 of those structs in an array, the address rules for the second
> > struct in the array are the same as for the first struct.
> > If that second struct would start at byte 10, this would not be true
> > so the compiler also inserts some padding at the end of the structure
> > so that the next struct after it starts at a multiple of the size of
> > its largest member.
> >
> >
> >
> >
> > On Jul 29, 3:36 pm, Arun Vishwanathan <aaron.nar...@gmail.com> wrote:
> >> @puneet : no , in this case since 4 bytes will be used for int a and int
> c
> >> and then 1 byte for char b with 3 padded bytes next..it wud be the same
> >> here
> >>
> >> On Fri, Jul 29, 2011 at 12:11 PM, Puneet Gautam
> >> <puneet.nsi...@gmail.com>wrote:
> >>
> >>
> >>
> >> > @nikhil: If i declare "Char b" after "int c".., would there be any
> >> > difference...?
> >>
> >> > On 7/28/11, Nikhil Gupta <nikhilgupta2...@gmail.com> wrote:
> >> > > Here's another example.
> >>
> >> > > struct example
> >> > > {
> >> > > int a;
> >> > > char b;
> >> > > int c;
> >> > > }
> >>
> >> > > Now if a variable of type example is declared then
> >> > > (considering base address as 2000)
> >> > > a gets : 2000 to 2003
> >> > > b gets : 2004
> >> > > c gets : 2005 to 2008 ? NO
> >>
> >> > > It gets 2008 to 2011. The bytes from 2005 to 2007 (3 bytes) are
> padded
> >> > > in
> >> > > this case.
> >>
> >> > > On Thu, Jul 28, 2011 at 12:18 AM, Aman Goyal <
> aman.goya...@gmail.com>
> >> > wrote:
> >>
> >> > >> yes this will be the case.
> >>
> >> > >> On Wed, Jul 27, 2011 at 11:35 PM, Puneet Gautam
> >> > >> <puneet.nsi...@gmail.com>wrote:
> >>
> >> > >>> @nikhil:So what u mean is that if i have:
> >>
> >> > >>> struct{
> >> > >>> int a;
> >> > >>> char b[5];
> >> > >>> };
> >>
> >> > >>> the size of this struct's node will be 12 not 9.., to make it a
> >> > multiple
> >> > >>> of 4??
> >>
> >> > >>> On 7/26/11, Nikhil Gupta <nikhilgupta2...@gmail.com> wrote:
> >> > >>> > Padding is not a topic of self referential structure.
> >>
> >> > >>> > Padding means that extra spaces of memory are used by the
> compiler
> >> > >>> > to
> >> > >>> > allocate memory. This is done to have the memory address as a
> >> > multiple
> >> > >>> of
> >> > >>> > the size of the variable. This speeds up the processing of these
> >> > >>> variables
> >> > >>> > by the compiler.
> >>
> >> > >>> > On Tue, Jul 26, 2011 at 8:09 PM, Puneet Gautam
> >> > >>> > <puneet.nsi...@gmail.com>wrote:
> >>
> >> > >>> >> what is meant by padding in self_referenced structure?
> >> > >>> >> Is it always necessary?
> >>
> >> > >>> >> --
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> >> > >>> > --
> >> > >>> > Nikhil Gupta
> >> > >>> > Senior Co-ordinator, Publicity
> >> > >>> > CSI, NSIT Students' Branch
> >> > >>> > NSIT, New Delhi, India
> >>
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> >> > > --
> >> > > Nikhil Gupta
> >> > > Senior Co-ordinator, Publicity
> >> > > CSI, NSIT Students' Branch
> >> > > NSIT, New Delhi, India
> >>
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> >> --
> >>  Arun Vish
> >> Graduate Student
> >> Department of Computer Science
> >> University of Southern California
> >
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