size of a structure

[mahiapkum]

hello,
I have a structure when i print the size of struture i get different values printed can anyone explain:

struct m{
unsigned int i;
unsigned long int j;
unsigned int l;
unsigned int k:2;
unsigned int m:2;
};
size is:24
what about bit fields????
struct m{
unsigned int i;
unsigned long int j;
unsigned int l;
unsigned int k:2;
unsigned int m:2;
}__attribute__( (__packed__));
size is:17
again what about bit fields???

the size of int on my machine is 32bits..

[arunraj2002in]

Byte is the lowest level at which we can access the data, there is no bit type.
In fact we can't perform operation on single bit(only by some tricks we can do).. every bit wise operation will be aplied on a entire byte at a time..
So even if u apply bit field it will be applied to byte.. now if you use pack the also it will take minimum of byte only.

--Arun--

[mahiapkum]

Byte is the lowest level at which we can access the data, there is no bit type.
In fact we can't perform operation on single bit(only by some tricks we can do).. every bit wise operation will be aplied on a entire byte at a time..
So even if u apply bit field it will be applied to byte.. now if you use pack the also it will take minimum of byte only.

--Arun--

My doubt is when i dont use packed the size of struct is 24 i.e size of long int ,is it that the size of other members of struct is based on the largest size member of struct.(here unsigned long int).But when i use packed the size is taken as normal size of members.
When i dont use packed as in the first case the size is 24 i.e size of unsigned long int,which is also taken as size for two unsigned ints, and what about the two bit fields of 2 bits each.If size of structure is based on largest member of struct wouldnt it be 32.

[kky2k]

My doubt is when i dont use packed the size of struct is 24 i.e size of long int ,is it that the size of other members of struct is based on the largest size member of struct.(here unsigned long int).But when i use packed the size is taken as normal size of members.
When i dont use packed as in the first case the size is 24 i.e size of unsigned long int,which is also taken as size for two unsigned ints, and what about the two bit fields of 2 bits each.If size of structure is based on largest member of struct wouldnt it be 32.

Though i can't understand ur question i can feel ur doubt...If i am right..
then Its about padding in structures
Let me explain that with a simple example,

struct m{
int a;
double b;
};

if u guess,the size of the above structure is 12 then u r wrong 'Coz its 16
y?
go thru this link

http://www.thescripts. com/forum/thread543879.ht ml

[mahiapkum]

Though i can't understand ur question i can feel ur doubt...If i am right..
then Its about padding in structures
Let me explain that with a simple example,

struct m{
int a;
double b;
};

if u guess,the size of the above structure is 12 then u r wrong 'Coz its 16
y?
go thru this link

http://www.thescripts. com/forum/thread543879.ht ml

Thanks for ur advice i understood.