Type Casting on Classes

In one previous post, I discussed about general type casting in C++. While in this post, I am going to talk about the casting on classes. More specifically, I won't discuss the keyword approach (static_cast, dynamic_cast, reinterpret_cast or const_cast) in this post.

Based on the is-a relationship between derived and base classes, implicit casting from derived class to base class is always possible for public inheritance (not possible for protected or private inheritance).

class Base {};
class Derived: public Base {};

Derived d;
Base b = d;

Without use of keywords, we may have 3 ways to convert unrelated class types.

1. Corresponding constructor
2. Overload assignment operator
3. Overload type casting operator

Suppose we want cast an object of class A to class B, then we may need define 1 or 2 in B's body, while define 3 in A's body.

Here is a sample code I wrote for testing. Note that the "=" sign in declaration is not assignment operator. Initialization, assignment, and explicit casting are all legal for Approaches 1 and 3, but only implicit casting by assignment is legal for Approach 2 with overloaded operator "=".



Related Posts:

Type Casting in C++

static_cast, dynamic_cast, and reinterpret_cast

Assignment between Class Objects