Editing Virtual method table (section)

==Invocation==
A call to <code>d->f1()</code> is handled by dereferencing <code>d</code>'s <code>D::B1</code> vpointer, looking up the <code>f1</code> entry in the virtual method table, and then dereferencing that pointer to call the code.

'''Single inheritance'''

In the case of single inheritance (or in a language with only single inheritance), if the vpointer is always the first element in <code>d</code> (as it is with many compilers), this reduces to the following pseudo-C++:

<syntaxhighlight lang="cpp">
(*((*d)[0]))(d)
</syntaxhighlight>
Where <code>*d</code> refers to the virtual method table of <code>D</code> and <code>[0]</code> refers to the first method in the virtual method table.  The parameter <code>d</code> becomes the [[This (computer science)|"<code>this</code>" pointer]] to the object.

'''Multiple inheritance'''

In the more general case, calling <code>B1::f1()</code> or <code>D::f2()</code> is more complicated:

<syntaxhighlight lang="cpp">
(*(*(d[0]/*pointer to virtual method table of D (for B1)*/)[0]))(d)   /* Call d->f1() */
(*(*(d[8]/*pointer to virtual method table of D (for B2)*/)[0]))(d+8) /* Call d->f2() */
</syntaxhighlight>

The call to <code>d->f1()</code> passes a <code>B1</code> pointer as a parameter.  The call to <code>d->f2()</code> passes a <code>B2</code> pointer as a parameter.  This second call requires a fixup to produce the correct pointer. The location of <code>B2::f2</code> is not in the virtual method table for <code>D</code>.

By comparison, a call to <code>d->fnonvirtual()</code> is much simpler:

<syntaxhighlight lang="cpp">
(*B1::fnonvirtual)(d)
</syntaxhighlight>