Understanding C Class Definitions Without Constructors but With Destructors

In C , if you define a class without explicitly defining a constructor but include a destructor, the class remains valid. The compiler will implicitly provide a default constructor that initializes member variables using their default constructors if needed. This article explains how this works and provides a practical example.

Key Points

Default Constructor: If no constructor is defined, the compiler creates a default constructor that does nothing. This constructor initializes member variables using their default constructors. Destructor: A destructor automatically calls when an object is destroyed, making it useful for resource cleanup and other necessary cleanup tasks.

Example of a Class Without a Constructor but with a Destructor

Consider the following simple example:

#include iostream
class MyClass {
public:
    ~MyClass() {  // Destructor
        std::cout Object destroyed
;
    }
};
int main() {
    MyClass obj;  // Default constructor is called implicitly
    // Destructor will be called automatically when obj goes out of scope
    return 0;
}

In this example, MyClass does not have a constructor, so the default constructor is used when creating the object obj.

When the obj goes out of scope, at the end of the main function, the destructor is called, printing Object destroyed.

Explanation

MyClass uses the default constructor, which means no specific initialization logic is executed. When obj goes out of scope, the destructor is automatically called, fulfilling its purpose of cleanup.

Summary

Defining a class without a constructor but with a destructor is perfectly valid in C . The default constructor is automatically provided, and the destructor is called when instances of the class are destroyed. This setup can be useful for managing resources without requiring special initialization logic.

When is an Empty Virtual Destructor Useful?

Sometimes, an empty virtual destructor can be useful. For example, a virtual destructor in a base class can prevent the compiler from optimizing away base class destructors, which might be necessary in polymorphic scenarios. However, an empty destructor in a class with no user-defined constructor should perform some task unrelated to mere destruction, like debugging specific parts of code or handling multi-threaded work. The key point is that all functions or operations should not generate exceptions.

Good luck with your coding endeavors!