Re: structures align

"SG" <s.gesemann@gmail.com> wrote in message
news:d43cc208-b5d0-4213-bf70-2fd5484b7990@v2g2000vbb.googlegroups.com...
alariq wrote:


FWIW, the construct above goes not give correct answer when you pass it a
reference. Here is an example:
______________________________________________________________
template<typename T>
struct my_helper {
    char c;
    T data;
};

#define aligned_at(C) ( sizeof(my_helper<C>) - sizeof(C) )

#include <cstdio>

#define ATTR_ALIGN(V) __attribute__((aligned(V)))

struct my_struct
{
    char ATTR_ALIGN(16) buffer;
};

int
main()
{
    {
        std::printf("my_struct = %lu\n"
                    "my_struct& = %lu\n",
                    (unsigned long)aligned_at(my_struct),
                    (unsigned long)aligned_at(my_struct&));
    }

    return 0;
}

______________________________________________________________

I am getting the following output:

my_struct = 16
my_struct& = 4294967288

<corrected align hack>
______________________________________________________________
template<typename T>
struct alignof_impl
{
    struct holder
    {
        T m_state;
    };

    struct aligner
    {
        char m_pad;
        holder m_holder;
    };
};

#define ALIGNOF(T) \
    (sizeof(alignof_impl<T>::aligner) - \
     sizeof(alignof_impl<T>::holder))

#define ATTR_ALIGN(V) __attribute__((aligned(V)))

#include <cstdio>

struct my_struct
{
    char ATTR_ALIGN(16) buffer;
};

int
main()
{
    {
        std::printf("my_struct = %lu\n"
                    "my_struct& = %lu\n",
                    (unsigned long)ALIGNOF(my_struct),
                    (unsigned long)ALIGNOF(my_struct&));
    }

    return 0;
}

______________________________________________________________

I get:

my_struct = 16
my_struct& = 4

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