What is purpose of a “this” pointer in C++? [duplicate]

Answer 1

One more purpose is to chaining object: Consider the following class:

class Calc{
private:
    int m_value;

public:
    Calc() { m_value = 0; }

    void add(int value) { m_value += value; }
    void sub(int value) { m_value -= value; }
    void mult(int value) { m_value *= value; }

    int getValue() { return m_value; }
};

If you wanted to add 5, subtract 3, and multiply by 4, you’d have to do this: #include int main() { Calc calc; calc.add(5); // returns void calc.sub(3); // returns void calc.mult(4); // returns void

    std::cout << calc.getValue() << '\n';
    return 0;
}

However, if we make each function return *this, we can chain the calls together. Here is the new version of Calc with “chainable” functions:

class Calc
{
private:
    int m_value;

public:
    Calc() { m_value = 0; }

    Calc& add(int value) { m_value += value; return *this; }
    Calc& sub(int value) { m_value -= value; return *this; }
    Calc& mult(int value) { m_value *= value; return *this; }

    int getValue() { return m_value; }
};

Note that add(), sub() and mult() are now returning *this. Consequently, this allows us to do the following:

#include 
int main()
{
    Calc calc;
    calc.add(5).sub(3).mult(4);

    std::cout << calc.getValue() << '\n';
    return 0;
}

We have effectively condensed three lines into one expression.

Copied from :http://www.learncpp.com/cpp-tutorial/8-8-the-hidden-this-pointer/