"Dev1024" <[EMAIL PROTECTED]> writes: > Having been a long time user of Microsoft Visual C++ .Net 2003 (MSVC), > I've recently been using g++ on a project. I've found a difference > between the two compilers when calling a virtual function that has me > puzzled.
The immediate question is "why do you care?" > The issue is when calling virtual functions. In MSVC the parameters > are pushed on to the stack as expected and then the address of the > function is loaded into EAX. Finally "call EAX" is issues to call the > virtual function. That is incorrect: you are missing a step: loading "this" into %esi. > In g++ (Cygwin g++ v3.4.4) the parameters are pushed > onto the stack as expected, but then a pointer (32 bit pointer in my > case) to the vtable is pushed on the stack as well That is also incorrect: it's the "this" parameter that is pushed. However, since g++ puts the vtable at the start of any class with virtual functions, the "this" and &vtbl are the same thing. > - Why does g++ load a pointer to the vtable on the stack after pushing > on the params? It doesn't. It simply passes all parameters (including "this") on the stack. > - Is there a compiler option that can be used to avoid putting a > pointer to the vtable on the stack? (I looked but couldn't find one.) These are implementation details, best left alone. Are you trying to link together MSVC and g++ compiled code? Cheers, -- In order to understand recursion you must first understand recursion. Remove /-nsp/ for email. _______________________________________________ help-gplusplus mailing list help-gplusplus@gnu.org http://lists.gnu.org/mailman/listinfo/help-gplusplus
