Padding and Alignment of Structure Members

The padding and alignment of members of structures (§3.5.2.1)

Structure members are aligned to the minimum of their own size or the current packing size. For 16-bit targets, the default packing size is 2. The default corresponds to the /Zp2 command-line option. The default packing size is 4 for 32-bit targets. See topic , “Storage and Alignment of Structures,” for more information.