On 23 August 2015 at 14:49, Jonathan Wakely wrote: > On 23 August 2015 at 12:05, Segher Boessenkool wrote: >> On Sun, Aug 23, 2015 at 12:15:56AM +0100, Jonathan Wakely wrote: >>> because alignments must be a power of 2. >> >> That is true in C++, but not true in C or even POSIX afaics? > > C11 §6.2.8 > > "Every valid alignment value shall be a nonnegative integral power of two." Anyway, the point is that John's assumption is wrong, you can have alignments larger than one and smaller than sizeof(int) in which case objects with those alignments don't have to be word-aligned. If you want to know whether an object will be word-aligned then use the alignof keyword, rather than incorrect assumptions.
