With the caveat that structs are padded by default so that members are aligned on architecture-friendly boundaries. For example, if a struct contains a char a

With the caveat that structs are padded by default so that members are aligned on architecture-friendly boundaries. For example, if a struct contains a char a followed by an int b, typically b would be at offset 4, even though sizeof(a) is 1. To get tight packing, you need to explicitly tell the compiler to disable padding.