- name: /LINKREPROFULLPATHRSP (Generate file containing absolute paths of linked files)

href: ../build/reference/link-repro-full-path-rsp.md

description: "Learn more about: Casting in C++"

The C++ language provides that if a class is derived from a base class containing virtual functions, a pointer to that base class type can be used to call virtual functions in the derived class object. A class containing virtual functions is sometimes called a "polymorphic class".

Class C with sub-objects B and A

Given an instance of class `C`, there is a `B` subobject and an `A` subobject. The instance of `C`, including the `A` and `B` subobjects, is the "complete object."

Since a derived class completely contains the definitions of all the base classes from which it is derived, it is safe to cast a pointer to any of the base classes (an upcast). Given a pointer to a base class, it may be safe to cast the pointer to an instance of a derived class (downcast). The actual object is said to be the "complete object." The pointer to the base class is said to point to a "subobject" of the complete object. For example, consider the class hierarchy shown in the following figure.

Using run-time type information, it is possible to check whether a pointer actually points to a complete object and can be safely cast to point to another object in its hierarchy. Use the [dynamic_cast](../cpp/dynamic-cast-operator.md) operator to make safe casts. It performs the run-time check necessary to ensure that the operation is safe.

For conversion of nonpolymorphic types, you can use the [static_cast](../cpp/static-cast-operator.md) operator (this topic explains the difference between static and dynamic casting conversions, and when it is appropriate to use each).