size of sturcture

[future]

struct knowsize
{
	int j;
	char i;
	char k;
	int j1;
}size;

printf("\nsizeof structure is%d",sizeof(size.j));
printf("\nsizeof structure is%d",sizeof(size.i));
printf("\nsizeof structure is%d",sizeof(size.k));
printf("\nsizeof structure is%d",sizeof(size.j1));


printf("\nsizeof structure is%d",sizeof(size));

output:

4
1
1
4

12

how this size of structure comes 12? I am not able to understand please clear this doubt.

[cyberfish]

j sits at 0-3
i at 4
k at 5
j1 cannot sit at 6 because it needs to be 32-bit aligned (multiple of 4), so it sits at 8-11

That's 12 bytes.

[future]

Thanks for clearing my doubt!!! buddy

[future]

char buff[30];

printf("\nthe length of buffer is %d",strlen(buff));

return 0;

o/p

the length of buffer is 43


Can you tell me the reason is it because of not initializing buffer with any value.

[Phenom]

The strlen function counts until it finds an '\0' terminating character. Since your buffer is not initialized the function starts counting ans stops when it finds an '\0', which in this case is 43 bytes after buff[0].

[claudiu]

It's not a DOUBT, it's a question!

I think someone else explained the difference on some other thread.

[Salem]

> the length of buffer is 43
or zero,
or -1
or why has my machine rebooted.

And yes, it is because your array is uninitialised.

[Elysia]

stlren does not find the size of a buffer; it finds the length of a string stored inside a buffer. And since you haven't stored any string inside the buffer, you invoke undefined behavior.

[nonoob]

Because you didn't initialize the buffer doesn't mean it contains all zeros. It contains garbage. Unless it's global.

[quzah]

Because you didn't initialize the buffer doesn't mean it contains all zeros. It contains garbage. Unless it's global.

Or static.


Quzah.

[iMalc]

j sits at 0-3
i at 4
k at 5
j1 cannot sit at 6 because it needs to be 32-bit aligned (multiple of 4), so it sits at 8-11

That's 12 bytes.

This may help:

printf("\noffset of structure is%d", &size.j - &size);
printf("\noffset of structure is%d", &size.i - &size);
printf("\noffset of structure is%d", &size.k - &size);
printf("\noffset of structure is%d", &size.j1 - &size);

[quzah]

Why don't you just use offsetof?

printf("\noffset of structure is%d",  offsetof( size.j ) );

Quzah.