Destructors in C++

What is a destructor?

A destructor is the opposite of a constructor: it runs automatically when an object is destroyed, giving it a chance to clean up — free memory, close files, release resources. Its name is the class name with a leading ~, and it takes no arguments.

Syntax and example

#include <iostream>
using namespace std;
class Logger {
public:
    Logger()  { cout << "Created\n"; }   // constructor
    ~Logger() { cout << "Destroyed\n"; } // destructor
};
int main() {
    Logger l;          // "Created"
    cout << "Working...\n";
    return 0;          // "Destroyed" runs here
}

When is it called?

• When a local object goes out of scope (its block ends).
• When a heap object is deleted.
• When the program ends, for objects still alive.

Local objects are destroyed in the reverse order they were created.

Freeing resources

The classic use is releasing memory a class allocated with new:

class Buffer {
    int *data;
public:
    Buffer(int n) { data = new int[n]; }   // acquire
    ~Buffer()     { delete[] data; }       // release
};

Because the destructor runs automatically, the memory is freed even if you forget — as long as the object is destroyed.

RAII and the rule of three

RAII — Resource Acquisition Is Initialization — is the C++ idea of tying a resource's lifetime to an object: acquire in the constructor, release in the destructor. It makes cleanup reliable even when errors happen.

The rule of three: if your class needs a custom destructor, it usually also needs a custom copy constructor and copy assignment operator, since all three deal with managing the resource. Modern C++ often avoids this entirely by using smart pointers.

Common mistakes

• Forgetting the ~, so it looks like a constructor.
• Giving a destructor parameters or a return type (it has neither).
• Needing a custom destructor but ignoring the rule of three (double free).
• Manually managing memory when a smart pointer would handle it automatically.

Summary

• A destructor runs automatically when an object is destroyed.
• Named ~ClassName(), with no arguments or return type.
• Called at end of scope, on delete, or at program end (reverse order).
• Used to free memory and release resources — the basis of RAII.
• A custom destructor usually means you need the rule of three.