How are objects stored in memory in C++?

Classes without virtual members and without inheritance are laid out in memory just like structs. But, when you start getting levels of inheritance things can get tricky and it can be hard to figure out what order things are in memory (particularly multiple inheritance).

When you have virtual members, they have a "vtable" in memory which contains pointers to the actual function which gets created based on the inheritance hierarchy of the class.

The bottom line is: don't access classes this way at all if you can avoid it (and also don't memset them or memcpy them). If you must do this (why?) then take care that you know exactly how your class objects are going to be in memory and be careful to avoid inheritance.

Almost. You cast to an Object*, and neglected to take an address. Let's re-ask as the following:

((int*)&myObject)[0] == i1

You have to be really careful with assumptions like this. As you've defined the structure, this should be true in any compiler you're likely to come across. But all sorts of other properties of the object (which you may have omitted from your example) will, as others said, make it non-POD and could (possibly in a compiler-dependent way) make the above statement not true.

Note that I wouldn't be so quick to tell you it would work if you had asked about i3 -- in that case, even for plain POD, alignment or endianness could easily screw you up.

In any case, you should be avoiding this kind of thing, if possible. Even if it works fine now, if you (or anybody else who doesn't understand that you're doing this trick) ever changes the structure order or adds new fields, this trick will fail in all the places you've used it, which may be hard to find.

Answer to your edit: If that's your entire class definition, and you're using one of the mainstream compilers with default options, and running on an x86 processor, then yes, you've probably guessed the right memory layout. But choice of compiler, compiler options, and different CPU architecture could easily invalidate your assumptions.