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);

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);

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.

The above is the detailed content of How Does C 's `dynamic_cast` Differ from `static_cast` in Runtime Type Checking?. For more information, please follow other related articles on the PHP Chinese website!