21.07.2014 16:32, Alex Peshkoff wrote:
> First of all - formal definition of API is certainly not a set of C++
> classes. Each firebird interface is a single pointer, pointing to the
> table of virtual functions that are contained in this interface. First
> parameter of each function is always a pointer to an interface itself.
>
> This definition in plain english may be rewritten in C:
> struct ISample
> {
> struct VTable
> {
> void functionOne(ISample* this, Type1 par1, Type2 par2, /*
> other parameters */);
> void functionTwo(ISample* this, TypeA parA, TypeB parB, /*
> other parameters */);
> /* other functions ... */
> };
>
> VTable* vTable;
> };
>
> Such definition of pure virtual interface should work and be correct for
> any working C compiler.
>
> [snip]
>
> in C++ we get exactly same binary layout for any known to us C++ compiler.
Is this really so? This is why I'm asking:
https://gcc.gnu.org/ml/gcc-help/2003-11/msg00257.html
http://stackoverflow.com/questions/5712808/understanding-the-vtable-entries
i.e. GCC has a different vtable layout and moreover it's version-dependent.
As for Free Pascal, they also reserve 12 bytes at the beginning of the
vtable, hence the compatibility issue.
Dmitry
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