Depends on compiler. In VC++, the vtable pointer stored at the beginning of the object allocation, before any member data. (Provided your class has at least one virtual member function.) There also may be multiple vtable pointers, if your class multiply-inherits from other classes with vtables. The vtables themselves are statically allocated somewhere in your … Read more
For HotSpot: The object header consists of a mark word and a klass pointer. The mark word has word size (4 byte on 32 bit architectures, 8 byte on 64 bit architectures) and the klass pointer has word size on 32 bit architectures. On 64 bit architectures the klass pointer either has word size, but … Read more
Both the C and C++ language standards make no requirements of struct padding and leave it to be a compiler implementation detail. A strict interpretation of this would mean that there is no guarantee a struct would be the same between the two. In practice, however, a given version of a toolchain capable of both … Read more