The short answer is you can't do it. The longer answer is that you can do it, but the details depend on your compiler. This particular bit-field layout looks suspiciously like it's supposed to map to a hardware register, in which case you've already got compiler dependencies: the details of how the bit-fields are arranged is implementation-defined. So while you're assuring yourself that the compiler lays them out the way you expect, you can also check whether it supports type puns through a union. Although writing to one field of a union and reading from another formally produces undefined behavior, both in C and in C++, most (all?) compilers support it in simple cases like this.
