On 8 September 2013 14:42, JimJoyce wrote: > > My question 'Are Structures doublewoord aligned?' was not about the second > half of the structure, but the beginning: an array of 9 ints. > It appears, having decided to place them on a doubleword boundary, it then > had to pad after the 9 ints to get back to an 8-byte boundary. Yes, there's a "hole" in the middle of the struct. > Was it pure mischance that the structure happened to start on a doubleword > that the extra int was needed. Had it started 4 bytes later, there would be > no padding? If you think about it that question doesn't make sense. The layout of a struct is always the same, irrespective of where an particular instance of that struct happens to be positioned in memory. A struct's definition does not "start" anywhere in memory, only an instance of the struct has an address. > Or do structures always start on a doubleword? It depends on the types in the struct and the ABI of the target platform. There's plenty of information about this on the web, e.g. http://en.wikipedia.org/wiki/Data_structure_alignment#Typical_alignment_of_C_structs_on_x86
