Hi Jacob, >-----Original Message----- >From: Jacob Smith [mailto:jnsmith@xxxxxxxx] >Sent: Wednesday, November 19, 2003 11:07 PM >To: Susantha Kumara >Subject: Re: differences of memory layout of virtual function table. > > >Virtual tables are never guaranteed for C++; specifically, GCC has been >known to deliberately break v-table hacks across implementations (you've >given examples yourself). Is there any documentation on HOW and WHY gcc does this ?. Please point me to any such documentation > There are a number of solutions for converting >an object to a basic C-type. I'd suggest one of those. If you need more >help, just post to the list. Please let me know what they are. But this mechanisms should not have any runtime overhead and could be used with most compilers. > >-j. > >btw, I believe the pointer order for the first offset into the function >table is dependent upon the number of virtual base classes the class >has, not some arbitrary number. > In our case we dont have any virtual base classes. Anyway knowing how exactly GCC does this is very important to me. please give me any links >Susantha Kumara wrote: > >>Hi all, >> >>I am writing a C Wrapper mechanism for C++ objects. Here the memory layout >>of the virtual table is very important. I am searching for the differences >>of memory layouts of the object/virtual pointer table(vtable) with various >>compilers (GCC, BC, VC++ etc). >> >>I found that there is a difference of the virtual tables between the GCC >>versions 2.96 and 3.2. The difference I found is in the offset for first >>virtual function pointer, >> * in GCC 2.96 4th pointer (12-16th bytes) is the pointer to the first >>virtual function, whereas >> * in GCC 3.2 3rd pointer (8-12th bytes) is the pointer to the first virtual >>function >> >>And in both GCC version I found that the pointer to the virtual destructor >>is placed just before the first virtual function pointer. Is this guarenteed >>always ?. >> >>Any help for me to figure out how GCC synthesizes an object is greatly >>appreciated. >> >>Thanks, >> >>Susantha. >> >> >> >> >> >> > Thanks in advance, Susantha.
