typeid

typeid — Runtime Type Information (RTTI)

The typeid operator provides runtime type information.
It returns a reference to a std::type_info object describing the type of an expression.

Use cases

• Checking the dynamic type of polymorphic objects.
• Debugging or logging type names.
• Comparing types at runtime.

Behavior

• For non-polymorphic types:
  typeid(expr) uses the static (compile-time) type.
• For polymorphic types (classes with virtual functions):
  typeid(*ptr) uses the dynamic (runtime) type if the expression is an lvalue to a polymorphic object.

Example

#include <iostream>
#include <typeinfo>

struct Base { virtual ~Base() {} };
struct Derived : Base {};

int main() {
    Base* p = new Derived;

    std::cout << typeid(*p).name();  // "Derived"  (dynamic type)
    std::cout << typeid(p).name();   // "Base*"    (static type)
}

✔️ Returned object

typeid returns a std::type_info object, which supports:

• .name()
• comparison via == and !=