Destructor role in C++ - Step-by-Step Execution

Concept Flow - Destructor role

Object Created

↓

Object Used

↓

Scope Ends or delete called

↓

Destructor Called

↓

Resources Freed

↓

Object Destroyed

When an object is no longer needed, its destructor runs automatically to clean up resources before the object is destroyed.

Execution Sample

C++

#include <iostream>

class MyClass {
public:
  ~MyClass() { std::cout << "Destructor called\n"; }
};

int main() {
  MyClass obj;
}

This code creates an object of MyClass and calls its destructor automatically when main ends.

Execution Table

Step	Action	Evaluation	Result
1	Enter main function	Start	main begins
2	Create object obj of MyClass	Constructor runs (default)	obj exists
3	Program runs inside main	No destructor called yet	obj usable
4	main function ends	Scope of obj ends	Trigger destructor
5	Destructor ~MyClass() called	Prints message	Output: Destructor called
6	Object obj destroyed	Memory freed	obj no longer exists

💡 Object goes out of scope, destructor runs, then program ends

Variable Tracker

Variable	Start	After Creation	After main ends
obj	does not exist	exists (in scope)	destroyed (out of scope)

Key Moments - 3 Insights

Why does the destructor run automatically without being called explicitly?

The destructor runs automatically when the object goes out of scope or is deleted, as shown in execution_table step 4 and 5.

What happens if the destructor is missing?

If no destructor is defined, C++ provides a default one that does basic cleanup, but custom resource cleanup won't happen.

Does the destructor run before or after the object is destroyed?

The destructor runs before the object is destroyed to free resources, as shown in execution_table step 5 before step 6.

Visual Quiz - 3 Questions

Look at the execution table, what happens at step 5?

A main function starts

B Object is created

C Destructor is called and prints a message

D Object is destroyed without destructor

💡 Hint

Check the 'Action' and 'Result' columns at step 5 in the execution_table

At which step does the object go out of scope triggering the destructor?

A Step 2

B Step 4

C Step 6

D Step 1

💡 Hint

Look for when 'Scope of obj ends' in the 'Evaluation' column

If the object was created with new, when would the destructor run?

A When delete is called on the pointer

B Immediately after creation

C Automatically at end of main

D Never

💡 Hint

Destructor runs when delete is called for objects created with new, not automatically at scope end

Concept Snapshot

Destructor role in C++:
- Destructor is a special function ~ClassName()
- Runs automatically when object goes out of scope or is deleted
- Cleans up resources like memory or files
- No need to call explicitly
- Helps prevent resource leaks

Full Transcript

In C++, a destructor is a special function that runs automatically when an object is no longer needed. This happens when the object goes out of scope or when delete is called on a pointer to the object. The destructor cleans up resources like memory or files to prevent leaks. In the example, the object 'obj' is created inside main. When main ends, obj goes out of scope, triggering the destructor which prints a message. After that, the object is destroyed and memory is freed. This automatic cleanup is important for safe and efficient programs.