What is a destructor in C ?
The destructor in C is a special member function that is automatically called when an object is out of scope or is explicitly deleted. Its main purpose is to clean up resources that an object may acquire during its life cycle, such as memory, file handles, or network connections. The destructor is automatically called in the following cases: when a local variable leaves scope, when a delete is called on the pointer, and when an external object containing the object is destructed. When defining the destructor, you need to add ~ before the class name, and there are no parameters and return values. If undefined, the compiler generates a default destructor, but does not handle dynamic memory releases. Notes include: Each class can only have one destructor and does not support overloading; it is recommended to set the destructor of the inherited class to virtual; the destructor of the derived class is executed first, and then the base class destructor is automatically called. When deleting derived class objects using base class pointers, the base class destructor must be virtual, otherwise the behavior is undefined. Although modern C recommends using smart pointers and RAII patterns, it is still important to understand the working mechanism of destructors, especially when dealing with legacy code or performance-sensitive systems.
A destructor in C is a special member function that gets called automatically when an object goes out of scope or is explicitly deleted. Its main job is to clean up resources that the object might have acquired during its lifetime — like memory, file handles, or network connections.
When Is a Destructor Called?
Destructors run automatically under certain conditions:
- When a local (automatic) variable goes out of scope
- When
deleteis called on a pointer to an object - When an object is part of another object (like a member variable), and the outer object's destructor runs
You don't need to call it manually unless you're managing raw points and using dynamic memory allocation.
Examples include:
- A class that opens a file in its constructor should close it in the destructor.
- An object that allocates memory with
newshould free it withdelete.
How to Define a Destructor
You define a destructor by putting a tilde ~ before the class name, and it takes no arguments and returns nothing:
class MyClass {
public:
~MyClass() {
// Cleanup code here
}
};If you don't define one, the compiler will generate a default destructor for you — but it won't handle custom cleanup like freeing dynamically allocated memory.
Some things to keep in mind:
- You can only have one destructor per class — no overloading
- It's good practice to make destructors virtual if your class is meant to be inherited from
Destructors and Inheritance
When dealing with derived classes:
- The destructor of the derived class runs first
- Then the base class destructor is called automatically
This ensures that anything set up by the base class is safely cleaned up after the derived class is done.
If you're deleting a derived class object through a base class pointer, always declare the base class destructor as virtual . Otherwise, the behavior is undefined.
So instead of this:
class Base {};Do this:
class Base {
public:
virtual ~Base() {}
};This small details helps prevent resource leaks in polymorphic types.
Final Notes
Destructors are cruel for proper resource management in C . While modern C encourages the use of smart points and RAII (Resource Acquisition Is Initialization), understanding how destructors work is still essential, especially when working with legacy code or performance-critical systems.
They aren't complicated, but they do require careful handling — especially when manual memory management is involved.
Basically that's it.
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