Difference between aligned malloc and standard malloc?

Question

I'm new to malloc and aligned malloc. I know how to use them. However, I don't know exactly in which case we should use aligned malloc instead of standard malloc. Can you explain it to me please?

Creatine

Language? I assume C, but you should also provide other environment details (OS, language implementation, etc). Standard C has only malloc, guaranteed to be correctly aligned for all standard data types. – Kimmie

I use in C11 standard in Ubuntu – Creatine

Added those as tags, please confirm and/or change as necessary. – Kimmie

I have put them as tags, sorry – Creatine

Answer 1

The glibc documentation makes it reasonably clear where you should use aligned_alloc:

The address of a block returned by malloc or realloc in GNU systems is always a multiple of eight (or sixteen on 64-bit systems). If you need a block whose address is a multiple of a higher power of two than that, use aligned_alloc or posix_memalign.

The C standard already guarantees that malloc will return a suitably aligned memory block for any of the standard types but there may be situations in which you want or need stricter alignment.

As one example, I seem to recall that SSE2 (SIMD) instructions need their data aligned on 16-byte boundaries so you could use aligned_alloc to give you that even on systems where malloc only guarantees alignment to an 8-byte boundary.

Kimmie