🟣 OOP · Lesson 41

this Pointer

Q: What is the this pointer in C++?

The this pointer is a hidden pointer available inside every non-static member function that points to the object the function was called on. It lets a member function refer to the current object explicitly, for example as this->name or by returning *this.

Q: What does return *this mean in C++?

Returning *this returns a reference to the current object itself. This enables method chaining, where several calls are written in a row like obj.setX(1).setY(2), because each function hands the same object back to the next call.

Q: What is the difference between this and *this in C++?

this is a pointer to the current object, so you use it with the arrow operator like this->member. *this dereferences that pointer to give the object itself, which is what you return when you want to return the current object by reference.

Written and reviewed by Gagan Bhardwaj · Senior IT Faculty · 15+ years’ experience

What is the this pointer?

Inside every non-static member function there is a hidden pointer called this, which points to the object the function was called on. When you write obj.method(), inside method the pointer this holds the address of obj.

Disambiguating names

The most common use: when a parameter has the same name as a data member, this-> makes clear which one you mean:

C++

#include <iostream>
using namespace std;
class Box {
    int width;
public:
    void setWidth(int width) {
        this->width = width;    // member = parameter
    }
    int getWidth() { return width; }
};
int main() {
    Box b;
    b.setWidth(50);
    cout << b.getWidth();   // 50
}

Output:
50

Here this->width is the member; plain width is the parameter.

Returning *this for chaining

If a member function returns *this (the current object by reference), you can chain calls one after another:

C++

class Builder {
    int x = 0, y = 0;
public:
    Builder& setX(int v) { x = v; return *this; }
    Builder& setY(int v) { y = v; return *this; }
    void show() { cout << x << "," << y << "\n"; }
};
int main() {
    Builder b;
    b.setX(3).setY(7).show();   // chained calls
}

Output:
3,7

Each setter returns the same object, so the next call continues on it.

Comparing objects

this also lets a function compare the current object with another, for example to check for self-assignment: if (this == &other) return *this;.

this and static functions

A static member function has no this pointer, because it is not tied to any object. That is why a static function cannot use per-object data directly.

Common mistakes

Using this.member (dot) instead of this->member (arrow) — this is a pointer.
Returning this instead of *this when you meant to return the object by reference.
Expecting this to exist in a static member function.
Overusing this-> where there is no name clash (it is optional then).

🏋️ Practice

Write a Rectangle class with setWidth and setHeight that each return *this, so you can write r.setWidth(4).setHeight(5). Add an area() and print the result of the chained calls.

Summary

this is a hidden pointer to the object a member function runs on.
Use this->name to tell a member from a same-named parameter.
Return *this to enable method chaining.
this is a pointer, so use the arrow operator with it.
Static member functions have no this pointer.

Frequently Asked Questions

What is the this pointer in C++?

The this pointer is a hidden pointer available inside every non-static member function that points to the object the function was called on. It lets a member function refer to the current object explicitly, for example as this->name or by returning *this.

Why is the this pointer used in C++?

It is used to tell a member and a parameter apart when they share a name, to return the current object so calls can be chained, and to pass the current object to another function. It makes "the object this function is running on" available by name.

What does return *this mean in C++?

Returning *this returns a reference to the current object itself. This enables method chaining, where several calls are written in a row like obj.setX(1).setY(2), because each function hands the same object back to the next call.

Does a static member function have a this pointer in C++?

No. A static member function belongs to the class rather than any object, so it has no this pointer and cannot refer to per-object members through it. Only non-static member functions receive a this pointer.

What is the difference between this and *this in C++?

this is a pointer to the current object, so you use it with the arrow operator like this->member. *this dereferences that pointer to give the object itself, which is what you return when you want to return the current object by reference.

this pointer क्या है?

हर non-static member function के अंदर एक छिपा pointer होता है जिसे this कहते हैं, जो उस object पर इशारा करता है जिस पर function call हुआ। जब आप obj.method() लिखते हैं, method के अंदर this pointer obj का address रखता है।

नाम स्पष्ट करना

सबसे आम इस्तेमाल: जब किसी parameter का नाम data member जैसा ही हो, this-> स्पष्ट करता है कि आप किसका मतलब रखते हैं:

C++

#include <iostream>
using namespace std;
class Box {
    int width;
public:
    void setWidth(int width) {
        this->width = width;    // member = parameter
    }
    int getWidth() { return width; }
};
int main() {
    Box b;
    b.setWidth(50);
    cout << b.getWidth();   // 50
}

Output:
50

यहाँ this->width member है; सादा width parameter है।

Chaining के लिए *this लौटाना

अगर कोई member function *this (वर्तमान object reference से) लौटाए, आप calls को एक के बाद एक chain कर सकते हैं:

C++

class Builder {
    int x = 0, y = 0;
public:
    Builder& setX(int v) { x = v; return *this; }
    Builder& setY(int v) { y = v; return *this; }
    void show() { cout << x << "," << y << "\n"; }
};
int main() {
    Builder b;
    b.setX(3).setY(7).show();   // chained calls
}

Output:
3,7

हर setter वही object लौटाता है, तो अगली call उसी पर जारी रहती है।

Objects की तुलना

this किसी function को वर्तमान object की दूसरे से तुलना भी करने देता है, जैसे self-assignment जाँचने को: if (this == &other) return *this;।

this और static functions

Static member function के पास कोई this pointer नहीं होता, क्योंकि यह किसी object से बँधा नहीं। इसीलिए static function per-object data सीधे इस्तेमाल नहीं कर सकता।

आम गलतियाँ

this->member (arrow) के बजाय this.member (dot) इस्तेमाल करना — this एक pointer है।
Object को reference से लौटाने का मतलब होने पर *this के बजाय this लौटाना।
Static member function में this के होने की उम्मीद करना।
जहाँ नाम टकराव न हो वहाँ this-> का अति-इस्तेमाल (तब यह वैकल्पिक है)।

🏋️ अभ्यास

एक Rectangle class लिखें जिसमें setWidth और setHeight हर एक *this लौटाएँ, ताकि आप r.setWidth(4).setHeight(5) लिख सकें। एक area() जोड़ें और chained calls का परिणाम print करें।

सारांश

this उस object का छिपा pointer है जिस पर member function चलता है।
Member को same-नाम parameter से अलग बताने को this->name इस्तेमाल करें।
Method chaining सक्षम करने को *this लौटाएँ।
this एक pointer है, तो इसके साथ arrow operator इस्तेमाल करें।
Static member functions के पास this pointer नहीं होता।

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