Question on bitfields & structs

[sarathy]

Hi,

1. I executed the following code. But could not deduce anything from
the results. Can anyone please help me out.

# include <stdio.h>

struct struct1{ const :16; volatile :4;};
struct struct2{ int :1; unsigned :1;
const :16; volatile :4;};

int main()
{
printf ("Size of struct 1 = %d\n",sizeof(st ruct struct1));
/* Prints 4 */
printf ("Size of struct 2 = %d\n",sizeof(st ruct struct2));
/* Prints 3 */
}

2. Also what is meant by "incomplete type" in C?
3. What does tag refer to in a struct/union declaration?

Regards,
Sarathy

[Flash Gordon]

sarathy wrote:

Hi,

1. I executed the following code. But could not deduce anything from
the results. Can anyone please help me out.

Please try to format your code moderately sensibly. What you have posted
is a complete mess.

# include <stdio.h>

struct struct1{ const :16; volatile :4;};

struct struct2{ int :1; unsigned :1;
const :16; volatile :4;};

int main()
{
printf ("Size of struct 1 = %d\n",sizeof(st ruct struct1));
/* Prints 4 */
printf ("Size of struct 2 = %d\n",sizeof(st ruct struct2));
/* Prints 3 */
}

In struct2 your compiler chose to insert some padding bits. I also
deduced that you probably have an 8 bit char type on your system and
that your compiler accepts structures without any named fields. I
further deduce that you don't know that sizeof does not return an int.

2. Also what is meant by "incomplete type" in C?

A type that is not complete.

3. What does tag refer to in a struct/union declaration?

It is its name, so it refers to the struct or union you are declaring.

Have you read the relevant sections of your C text book yet?
--
Flash Gordon, living in interesting times.
Web site - http://home.flash-gordon.me.uk/
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