Structures with bitwise data in C++ [duplicate]

Answer 1

An alternative to the undefined behavior that comes from the union technique, you could copy the data:

mystruct m;
m.Reserved1 = 0;
m.WordErr = 1;
m.SyncErr = 0;
m.WordCntErr = 0;
m.Reserved2 = 0;

uint16_t value = 0;
memcpy(&value, &m, sizeof(value));

[Code]

Of course, the output is platform-specific / endian-sensitive, so if you plan on writing it out so you can read it in again then take that into account.