https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77388
--- Comment #4 from rguenther at suse dot de <rguenther at suse dot de> --- On Fri, 26 Aug 2016, andre.simoesdiasvieira at arm dot com wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77388 > > --- Comment #3 from Andre Vieira <andre.simoesdiasvieira at arm dot com> --- > Thank you Richard! > > I have a follow up question. Why is this only a problem when passing by > reference and not when passing a pointer? > > So say: > #define PACKED __attribute__ ((packed)) > > #define TYPE_C short > > typedef struct { > TYPE_C c; > } PACKED test_struct; > > class A > { > const TYPE_C * c; > public: > A (const TYPE_C * _c) : > c(_c) {}; > }; > > class B > { > public: > B(); > A foo (); > private: > test_struct * s; > }; > > A B::foo () > { > return A (&(s->c)); > } > > Wouldn't there still be an alignment mismatch between A::c and s->c? Yes, this still invokes undefined behavior. You just don't get bitten by the C++ FE choosing to use a temporary for the const reference. I suppose using a non-const reference would "work" as well. Note the above is also not diagnosed.
