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Re: standards/52571: max_align_t has smaller alignment than double

On Mon, Sep 25, 2017 at 04:55:00PM +0000, wrote:
> max_align_t is supposed to have the largest alignment among the
> standard C types. But here, __alignof__(max_align_t) < __alignof__(double).

So this one is a nice excercise in GCC extensions and why they sometimes
don't give you what you think they do. Compare the following test case
on i386 with and without USE_ALIGNOF:

#include <stddef.h>

struct foo {
  double x;
  char t;

int main() {
  return __alignof__(double);
  return sizeof(struct foo) - offsetof(struct foo, t);


For the SYSV ABI (not the bastardized version Linux is nowadays using),
the ABI alignment of double is 32bit, but most compiler use a prefered
alignment of 64bit. Similar for long double.


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