object-layout

I found this in a website while reading about virtual inheritance in c++ When multiple inheritance is used, it is sometimes necessary to use virtual inheritance. A good example for this is the standard iostream class hierarchy: //Note: this is a simplified description of iostream classes class ostream: virtual public ios { /*..*/ } class istream: virtual public ios { /*..*/ } class iostream : public istream, public ostream { /*..*/ } //a single ios inherited How does C++ ensure that only a single instance of a virtual member exists, regardless of the number of classes derived from it? C++ uses

Could you give me some information on what is exactly stored in object header? I know, that it's probably JVM dependent, but maybe for HotSpot at least? I'm looking for exact description specifically for a first row. I've read several information that I can't verify positively with information I find. Maybe you have a link to OpenJDK wiki that says it all? box 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