What is the recommended way to align memory in C++11

Question

I am working on a single producer single consumer ring buffer implementation.I have two requirements:

1. Align a single heap allocated instance of a ring buffer to

Answer 1

After some more research my thoughts are:

1. Like @TemplateRex pointed out there does not seem to be a standard way to align to more than 16 bytes. So even if we use the standardized alignas(..)there is no guarantee unless the alignment boundary is less than or equal to 16 bytes. I'll have to verify that it works as expected on a target platform.

2. __attribute ((aligned(#))) or alignas(..) cannot be used to align a heap allocated object as I suspected i.e. new() doesn't do anything with these annotations. They seem to work for static objects or stack allocations with the caveats from (1).

   Either posix_memalign(..) (non standard) or aligned_alloc(..) (standardized but couldn't get it to work on GCC 4.8.1) + placement new(..) seems to be the solution. My solution for when I need platform independent code is compiler specific macros :)

3. Alignment for struct/class fields seems to work with both __attribute ((aligned(#))) and alignas() as noted in the answer. Again I think the caveats from (1) about guarantees on alignment stand.

So my current solution is to use posix_memalign(..) + placement new(..) for aligning a heap allocated instance of my class since my target platform right now is Linux only. I am also using alignas(..) for aligning fields since it's standardized and at least works on Clang and GCC. I'll be happy to change it if a better answer comes along.