Object lifecycle in C++ - Step-by-Step Execution

Concept Flow - Object lifecycle

Object Declaration

↓

Constructor Called

↓

Object in Use

↓

Destructor Called

↓

Object Destroyed

This flow shows how an object is created, used, and then destroyed in C++.

Execution Sample

C++

#include <iostream>
class MyClass {
public:
  MyClass() { std::cout << "Constructor\n"; }
  ~MyClass() { std::cout << "Destructor\n"; }
};

int main() {
  MyClass obj;
}

This code creates an object of MyClass, calls its constructor, then calls its destructor when main ends.

Execution Table

Step	Action	Output	Object State
1	Enter main function		No object
2	Declare obj of MyClass	Constructor	Object created
3	Use obj (no output here)		Object alive
4	Exit main function	Destructor	Object destroyed

💡 Program ends, destructor called, object lifecycle complete

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4
obj	Not declared	Constructed	Alive	Destroyed

Key Moments - 3 Insights

Why do we see 'Constructor' printed before 'Destructor'?

The constructor runs when the object is created (Step 2), and the destructor runs when the object goes out of scope at the end of main (Step 4), as shown in the execution_table.

Does the destructor run automatically or do we call it?

The destructor runs automatically when the object is destroyed (Step 4). We do not call it manually, as shown by the output in the execution_table.

What happens if we declare the object inside a block?

The constructor runs when declared, and the destructor runs when the block ends, similar to Steps 2 and 4 but earlier. The lifecycle is the same but scoped to the block.

Visual Quiz - 3 Questions

Look at the execution_table, what is the state of 'obj' after Step 3?

A Object destroyed

B Object alive

C Object not declared

D Constructor running

💡 Hint

Check the 'Object State' column for Step 3 in the execution_table.

At which step does the destructor run according to the execution_table?

A Step 4

B Step 3

C Step 2

D Destructor never runs

💡 Hint

Look at the 'Output' column for the destructor call in the execution_table.

If we remove the object declaration, what output will the program produce?

A Constructor and Destructor

B Only Constructor

C No output

D Only Destructor

💡 Hint

Without object declaration, constructor and destructor are not called, so no output appears.

Concept Snapshot

Object lifecycle in C++:
- Object declared -> constructor runs
- Object used while alive
- Object destroyed -> destructor runs
- Constructor and destructor manage setup and cleanup
- Destructor runs automatically at scope end

Full Transcript

This example shows the lifecycle of an object in C++. When the object 'obj' is declared in main, the constructor runs and prints 'Constructor'. The object stays alive during the main function. When main ends, the destructor runs automatically and prints 'Destructor'. This shows how C++ manages object creation and destruction automatically based on scope.