Question

The output of this program is 28. I don’t understand how?
According to me this should be 32(4+4+4+4+12)+4(to maintain the alignment)=32.
Please explain the reason for displaying the output 28??

struct test{
    char c;
    int d;
    int x;
    int y;
    long double p;
    }t1;

printf("%d",sizeof(t1));

Answer 1

Maybe your “long double” is actually the same as a double (8 bytes), and if you’re on a 32bit processor the alignment is 4-byte.

4+4+4+4+8 = 24

What is sizeof(long double)?

EDIT:

I used GCC’s __builtin_offset_of() and __alignof__ to investigate. The actual answer that explains the size of the struct is:

4+4+4+4+12 = 28

sizeof(long double) is 12.

No padding is necessary because __alignof__(long double) is 4 and. Interestingly, __alignof__(double) is 8.