How Can I Implement Java's `instanceof` Operator in C ?

In C , achieving the equivalent functionality of Java's instanceof operator involves a technique known as runtime type identification (RTTI) using dynamic_cast. This allows you to verify whether a given object, stored as a pointer or reference to its base class, points to a specific derived class instance.

To check if an object pointed to by a pointer or reference to the base class (old) is of a specific derived class type (NewType), you can use the following syntax:

if(NewType* v = dynamic_cast<NewType*>(old)) {
   // old was safely casted to NewType
   v->doSomething(); // Access specific methods of NewType
}

It's important to note that dynamic_cast requires compiler support for RTTI, which must be enabled during compilation.

However, it's crucial to carefully consider the necessity of dynamic_cast before using it. In general, it indicates a potential design issue. One should strive for more robust and type-safe approaches, such as:

• Defining a virtual function in the base class that exhibits specific behavior for each derived class.
• Utilizing a visitor pattern that allows for specific behavior for subclasses without modifying the interface.
• Employing a simple and lightweight hack by introducing an enum representing different object types and comparing to the appropriate type.
• Keeping in mind that dynamic_cast does not support multiple levels of inheritance.

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