C++ typeid

🔎 C++ typeid – Discover the Real Type of an Object

The typeid keyword in C++ helps you check the real type of a variable while the program is running. It’s like saying, “Who are you really?” 🤔

This is especially useful when you’re working with pointers, references, and polymorphism.

🛠️ Syntax of typeid

typeid(expression).name()

It returns the type of the expression — the actual data type, not just the one you declared it as.

🔧 Example: Simple typeid usage

#include <iostream>
#include <typeinfo>
using namespace std;

int main() {
    int a = 42;
    double b = 3.14;
    char c = 'A';

    cout << "a is: " << typeid(a).name() << endl;
    cout << "b is: " << typeid(b).name() << endl;
    cout << "c is: " << typeid(c).name() << endl;

    return 0;
}
  

🧬 Example with Polymorphism

Let’s see how typeid reveals the actual object type when using base class pointers.

#include <iostream>
#include <typeinfo>

using namespace std;

class Animal {
public:
    virtual void speak() {}
};

class Dog : public Animal {};
class Cat : public Animal {};

int main() {
    Animal* a = new Dog();
    cout << "Actual type: " << typeid(*a).name() << endl;

    delete a;
    return 0;
}
  

🎯 Remember

• typeid returns the real runtime type
• Works best with pointers and polymorphism
• You must use virtual functions in the base class for accurate results