🔍 C++ RTTI (Run-Time Type Information) – Identify Object Types at Runtime

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🧲 Introduction – Why Use RTTI in C++

C++ is a statically-typed language, but in polymorphic scenarios, it’s sometimes essential to determine the actual type of an object at runtime. This is where RTTI (Run-Time Type Information) comes in. It helps in safe typecasting, type checks, and debugging without breaking type safety.

🎯 In this guide, you’ll learn:

• What RTTI is and how it works
• How to use typeid and dynamic_cast
• Real-world examples of RTTI
• Best practices and limitations

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🔍 What Is RTTI?

RTTI (Run-Time Type Information) allows C++ programs to determine object types during execution. It works only with polymorphic classes (classes with at least one virtual function) and is enabled by default unless explicitly disabled.

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🧠 Key RTTI Operators

Operator	Description
typeid	Returns the actual type of an expression/object
dynamic_cast	Safely casts pointers/references in class hierarchies

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💻 Code Examples – With Output

✅ Example 1: Using typeid for Type Identification

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

class Animal {
public:
    virtual ~Animal() {}
};

class Dog : public Animal {};

int main() {
    Animal* a = new Dog();
    cout << typeid(*a).name() << endl;  // Output: class Dog (implementation-defined)
    delete a;
}

🟢 Output: Implementation-defined name like Dog or class Dog

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✅ Example 2: Safe Downcasting with dynamic_cast

Animal* a = new Dog();
Dog* d = dynamic_cast<Dog*>(a);

if (d) {
    cout << "Downcast successful" << endl;
} else {
    cout << "Invalid cast" << endl;
}

🔐 If cast fails, dynamic_cast returns nullptr for pointers or throws bad_cast for references.

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🚨 dynamic_cast vs static_cast

Feature	dynamic_cast	static_cast
Runtime check	✅ Yes	❌ No
Polymorphic req	✅ Yes (base class must be virtual)	❌ No
Safe casting	✅	⚠️ Risk of undefined behavior

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📘 When to Use RTTI

• Type-checking in polymorphic object hierarchies
• Safe downcasting in class hierarchies
• Logging and debugging object types
• Implementing serialization, plugin systems, interpreters

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💡 Best Practices & Tips

📘 Always ensure base class has a virtual destructor to enable RTTI
💡 Use dynamic_cast only when necessary—prefer virtual function overrides where possible
⚠️ Avoid RTTI in performance-critical code (may introduce overhead)

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🛠️ Use Cases for RTTI

📦 Plugin Systems: Detect and cast plugin types dynamically
🎮 Game Engines: Downcast base Entity to specific subclasses like Player or Enemy
🧪 Debugging Tools: Log types during testing or fault tracing
📁 File Parsers: Handle polymorphic file sections or formats safely

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📌 Summary – Recap & Next Steps

🔍 Key Takeaways:

• RTTI enables type inspection and safe downcasting at runtime
• Use typeid to get the real type; dynamic_cast to convert safely between base and derived pointers
• Only works with polymorphic types

⚙️ Real-World Relevance:
RTTI is crucial in extensible systems, type inspection tools, complex class hierarchies, and polymorphic containers.

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❓FAQ – C++ RTTI

❓ What is RTTI used for?
✅ For identifying and safely casting object types at runtime in polymorphic hierarchies.

❓ Is RTTI enabled by default?
✅ Yes, unless explicitly disabled by compiler flags.

❓ What happens if dynamic_cast fails?
✅ Returns nullptr for pointers, throws bad_cast for references.

❓ Can I use RTTI with non-polymorphic classes?
❌ No. The base class must have at least one virtual function.

❓ Does typeid work with references and pointers?
✅ Yes. Use typeid(*ptr) to get the dynamic type, not the static one.

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