Explain vTable and vptr.

vTable is a table containing function pointers. Every class has a vTable. vptr is a pointer to vTable. Each object has a vptr. In order to maintain and use vptr and vTable, the C++ compiler adds additional code at two places:

1. In every constructor – This code sets vptr:
   1. Of the object being created
   2. To point to vTable of the class
2. Code with the polymorphic functional call – At every location where a polymorphic call is made, the compiler inserts code in order to first look for vptr using the base class pointer or reference. The vTable of a derived class can be accessed once the vptr is successfully fetched. The address of the derived class function show() is accessed and called using the vTable.