Hi Eljay, I find in GCC and VC++ the pointer to the virtual table is the first pointer of the object. Is there any other known compiler to you that synthesizes a C++ object a different way ?. Regarding the Virtual table, offsets and function pointer ordering , I find its compiler dependant. >-----Original Message----- >From: Eljay Love-Jensen [mailto:eljay@xxxxxxxxx] >Sent: Wednesday, November 19, 2003 6:49 PM >To: Susantha Kumara >Subject: Re: differences of memory layout of virtual function table. > > >Hi Susantha, > >One C++ layout is adding an entry into a map of <addr,vtable> which is then accessed when fetching the vtable (which includes RTTI). > Which compilers do have this way ? Is this when we have virtual base classes ? >Another one is having the entire C++ vtable precede each object. (There are situations where this is preferable.) Is this preffered for performance reasons or comply with a common standard with the compilers ? > >For GCC in particular, I don't have any specific insight. > >But I suspect that what you want to do could better be done by making entry point static functions that do something like this: > >class Foo >{ >public: > virtual int zap(int i, int j); > static int Zap(Foo* p, int i, int j); >}; > >// Thunk function. >int Foo::Zap(Foo* p, int i, int j) >{ > return p->zap(i, j); >} I will try this way and let you know if I succeeds. thanks for the idea. > >That's more portable, and can be called from C (albeit with name mangling... I consider that a different issue and there are means to address that as well). > >Yet another radical alternative is to implement classes as C structs and hand-cobble the vtable. This is I think what I do. Here we have to know how each compiler do. > >HTH, >--Eljay > Thanks, Susantha.
