https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100224
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- (In reply to Zhao Chun from comment #2) > (In reply to Richard Biener from comment #1) > > You are accessing 'double' via a pointer to uint64_t * here: > > > > k = *((uint64_t*)data); > > > > that violates type based aliasing rules. You can use -fno-strict-aliasing > > to work around your bug or use > > > > typedef uint64_t aliasing_uint64_t __attribute__((may_alias)); > > k = *((aliasing_uint64_t*)data); > > Thanks for your answer, it works for me. > > However I don't quite understand why it works after such a change. Could you > please explain it more clearly? Using a may_alias attributed type tells GCC to treat it like a 'character type' in terms of what the C/C++ standards allow. Note that this is not portable. A solution that works with all compilers I know is doing memcpy (&k, data, sizeof (uint64_t));
