Struct definition as following(on 32-bit Linux):
#pragma pack(push, 8)
struct MY_STRUCT
{
char a[2];
short b;
short c;
short d;
int e;
long long x;
long long y;
};
#pragma(pop)
During the test, result of 'sizeof(struct MY_STRUCT)' is 28. Why not 32?
As I had expected, a,b,c,d will be packed into one 8-byte, e one and x, y
two. Ain't I right?
If I get wrong usage of #pragma pack(), could anyone please tell me how to
get it work correctly?
BTW, what on earth is the difference between __attribute__ align() and
#pragma pack()?
Thanks in advance!
3  4762 
On Jul 3, 3:14 pm, "Jimmy" <lofe...@yahoo. com.cnwrote:
Struct definition as following(on 32-bit Linux):
During the test, result of 'sizeof(struct MY_STRUCT)' is 28. Why not 32?
As I had expected, a,b,c,d will be packed into one 8-byte, e one and x, y
two. Ain't I right?
This is OT here but anyway... assuming this is gcc then 28 bytes is
correct, I don't know why you'd expect otherwise. Note that for x86
gcc usually defines:
char: 1 byte
short: 2 bytes
long: 4 bytes
int: 4 bytes
long long: 8 bytes
Therefore, your struct is:
struct MY_STRUCT
{
char a[2]; /* 2 */
short b; /* 2 */
short c; /* 2 */
short d; /* 2 */
int e; /* 4 */
long long x; /* 8 */
long long y; /* 8 */
/* total: 28 */
};
YMMV since gcc can be modified and recompiled to have different sizes
for variables. But for the sake of being able to correctly compile the
Linux TCP/IP stack this is the most common configuration on most 32bit
(and even most newer 64bit) machines.
Jimmy wrote:
>
.... snip ...
>
BTW, what on earth is the difference between __attribute__ align()
and #pragma pack()?
None. Neither exist in standard C. Find a suitable newsgroup.
--
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