How Does C 's `dynamic_cast` Differ from `static_cast` in Runtime Type Checking?

Understanding dynamic_cast in C

dynamic_cast, as the name suggests, enables runtime type checking for pointer and reference conversions in C . Unlike static_cast, which performs compile-time conversion, dynamic_cast makes the verification at execution time.

To grasp the concept of dynamic_cast in C , let's compare it to the C language.

static_cast

static_cast<type>(ptr);</type>

This performs a type conversion from ptr to Type* at compile time. However, it assumes the types are related and requires them to be compatible. If the conversion is not valid, the program will fail to compile.

dynamic_cast

dynamic_cast<type>(ptr);</type>

Similar to static_cast, dynamic_cast attempts to convert the pointer ptr to Type*. However, this conversion occurs at runtime. This allows for more flexibility, especially when dealing with inheritance and polymorphism.

In the provided example:

• dynamic_cast(ap) successfully converts ap to a B* because B is derived from A.
• dynamic_cast(ap) and dynamic_cast(b) also work correctly.
• dynamic_cast(ap) returns NULL because C is not derived from A.
• For references, dynamic_cast(&*ap) and dynamic_cast(&*ap) both succeed, while dynamic_cast(&*ap) throws a std::bad_cast exception.

Rules for Dynamic_cast:

• Base-to-derived (B2D) Casts: These casts always return a valid pointer if the pointer points to an object of the specified type. If the pointer doesn't point to an object of the correct type, a NULL pointer is returned.
• Derived-to-base (D2B) Casts: These casts always succeed and return a valid pointer. The exception occurs when attempting to cast an empty pointer to a derived type, which results in a NULL pointer.

Remember that for base-to-derived casting, the classes involved must be polymorphic. This means they must have at least one virtual function declared in their base class.

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