What is the this Pointer in C++?

Expected Interview Answer

Step-by-Step Explanation

1. Step 1

   Call a member function on an object

   When you write obj.method(), the compiler passes the address of obj as the hidden this argument.

2. Step 2

   Access members through this

   Inside the method, this->member refers to the calling object's data or functions.

3. Step 3

   Disambiguate names

   When a parameter shares a member's name, use this->name to refer to the member explicitly.

4. Step 4

   Return *this for chaining

   Return a reference to the object so calls like obj.setA(1).setB(2) work fluently.

5. Step 5

   Respect const-ness

   In a const member function this is const ClassName*, so you cannot modify members through it.

Code Example

#include <iostream>

class Box {
    int width;
    int height;
public:
    Box& setWidth(int width) {
        this->width = width;   // 'this->' picks the member over the parameter
        return *this;          // return the object for chaining
    }
    Box& setHeight(int height) {
        this->height = height;
        return *this;
    }
    void print() const {
        std::cout << width << " x " << height << '\n';
    }
};

int main() {
    Box b;
    b.setWidth(10).setHeight(5).print();  // chained calls
    return 0;
}

Follow-up Questions

• Why is the this pointer not available in static member functions?
• What is the type of this inside a const member function?
• How does returning *this enable method chaining?
• What is the difference between this and *this?
• Can you delete an object using this within its own method, and is it safe?