Editing Virtual method table (section)

==Multiple inheritance and thunks==
The g++ compiler implements the [[multiple inheritance]] of the classes <code>B1</code> and <code>B2</code> in class <code>D</code> using two virtual method tables, one for each base class. (There are other ways to implement multiple inheritance, but this is the most common.) This leads to the necessity for "pointer fixups", also called [[Thunk (programming)|thunk]]s, when [[Type conversion|casting]].

Consider the following C++ code:
<syntaxhighlight lang="cpp">
D  *d  = new D();
B1 *b1 = d;
B2 *b2 = d;
</syntaxhighlight>
While <code>d</code> and <code>b1</code> will point to the same memory location after execution of this code, <code>b2</code> will point to the location <code>d+8</code> (eight bytes beyond the memory location of <code>d</code>). Thus, <code>b2</code> points to the region within <code>d</code> that "looks like" an instance of <code>B2</code>, i.e., has the same memory layout as an instance of <code>B2</code>.{{clarify |reason=because it is not apparent why this should be so, and I am not even sure that the description is accurate if it is truly that way |date=August 2023}}