Is gcc's __attribute__((packed)) / #pragma pack unsafe?

Question

In C, the compiler will lay out members of a struct in the order in which they\'re declared, with possible padding bytes inserted between members, or after the last member,

Answer 1

It's perfectly safe as long as you always access the values through the struct via the . (dot) or -> notation.

What's not safe is taking the pointer of unaligned data and then accessing it without taking that into account.

Also, even though each item in the struct is known to be unaligned, it's known to be unaligned in a particular way, so the struct as a whole must be aligned as the compiler expects or there'll be trouble (on some platforms, or in future if a new way is invented to optimise unaligned accesses).