* Jonathan Wakely via Gcc: > On Tue, 7 Jan 2025, 03:09 M Chhapgar via Gcc, <gcc@gcc.gnu.org> wrote: > >> Hello, >> >> I am learning about memory alignment and noticed that on my x86-64 machine >> with GCC 14, a `complex double` has a size of 16 bytes, but an alignment of >> only 8 bytes. I am curious as to why this is. > > > Because it's roughly equivalent to: > > double arr[2]; > > This also has size 16 and alignment 8.
Well, the story is a bit more complicated. Array variables that are at least 16 bytes large have 16 byte alignment. This rule does not apply to struct members. The x86-64 ABI currently does not specify alignment for _Complex or _Atomic types. Thanks, Florian
