lmr (ren@math.ohio-state.edu) wrote:
: g++ compiled program tells me that sizeof(A)=1.
: Why 1 and what is this byte used for (storing ...??).

This correspond to a requirement by the C++ standard proposal that an
empty object has nonzero size (chapter 9 verse 3):

A class with an empty sequence of members and base class objects is an
empty class.  Objects of an empty class have a nonzero size.

: If I add several virtual functions, the sizeof(A) becomes 4, what are
: those four bytes for? A pointer to where the virtual functions are?

Yes: If virtual functions are used these have to be dispatched at run
time.  This could be done using a pointer to a table (the virtual
function table) where the actual address of the function is looked up.
There are other concepts around but I think it is sufficient and legal
to imagine the use of virtual functions this way.

dk
--
http://www.informatik.uni-konstanz.de/~kuehl
dietmar.kuehl@uni-konstanz.de
I am a realistic optimist - that's why I appear to be slightly pessimistic

If I define an empty class such as:

class A{

};

g++ compiled program tells me that sizeof(A)=1.
Why 1 and what is this byte used for (storing ...??).

If I add several virtual functions, the sizeof(A) becomes 4, what are
those four bytes for? A pointer to where the virtual functions are?

Many thanks
--
Liming Ren                       |
Dept. of Mathematics             |  231 West 18th Avenue
The Ohio State University        |  Columbus, Ohio43210