Re: Alignment

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Mon, 2 Mar 2009 02:37:48 -0800 (PST)
Message-ID:
<891084b3-ce7d-4a9a-b893-14499e22a2bc@j35g2000yqh.googlegroups.com>
On Feb 27, 4:15 am, "Chris M. Thomasson" <n...@spam.invalid> wrote:

<better_cs_...@yahoo.com> wrote in message

news:eab8ea3f-5616-4fd8-b2b0-16f86fe0b7a8@q1g2000vbn.googlegroups.com...

Please consider the two definitions below:

Foo foo;
unsigned char foo[sizeof(Foo)];

Are these guaranteed to have the same alignment, or will the
second definition have an alignment that is only modulo 1?


You can attempt to calculate alignment of `Foo' objects like this:


Which isn't what he needs, but...

___________________________________________________________________
#include <cstddef>
#include <cstdio>

struct Foo {
  char a;
  int b;
  double c;

  Foo(int b) {
    // [...];
  }
};

template<typename T>
size_t get_type_alignment() {
  struct aligner {
    char m_pad;
    T m_obj;
  };
  return offsetof(aligner, m_obj);


This is undefined behavior if T isn't a POD (and Foo isn't). It
won't compile with at least one compiler I use.

}


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