this pointer - C++

Posted 03-13-2012 at 11:10 AM by Aquarius_Girl
Updated 03-13-2012 at 10:25 PM by Aquarius_Girl

Quote:

The this pointer is a hidden pointer inside every class's non-static function which points to the class's particular object through which the concerned function is called.

Example:

Code:

class A
{
    private:
        int rollNumber;

    public:
	A (int rollNum)
	{
	    rollNumber = rollNum;
	}

	void setRollNumber (int rollNum)
	{
	    rollNumber = rollNum;
	}
};

int main ()
{
    A obj (1);
    obj.setRollNumber (2);
}

When we call a member function through an object of a
class, C++ internally passes a reference of that object
as an additional parameter to the function. Therefore,
this function call `obj.setRollNumber (2);` will
internally look like:

Code:

obj.setRollNumber (&obj, 2);

Also, the function definition will be reformed as follows:

Code:

void setRollNumber (A *const this, int rollNum)
{
    this->rollNumber = rollNum;
}

Returning this pointer will return a reference to the object that
was implicitly passed to the function by C++.
Example:

Code:

class B
{
    private:
	int sum;

    public:
	B (int number)
	{
	    sum = 0;
	    sum =+ number;
	}

	void add (int number)
	{
	    sum =+ number;
	}
};

int main ()
{
    B obj (1);

    // One way of adding the numbers is by calling the function `add ()` individually three times through the object `obj`.
    obj.add (2);
    obj.add (3);
    obj.add (4);
}

Another way of writing the same is:
Example:

Code:

class B
{
    private:
        int sum;

    public:
	B ()
	{
	    sum = 0;
	}

	B& add (int number)
	{
	    sum =+ number;

            // Returning the reference to the object through which this function will get called.
	    return *this;
	}
};

int main ()
{
    B obj;

    obj.add (1).add (2).add (3). add (4);
}

`obj.add (1).add (2).add (3). add (4);` In this statement the first
call to `obj.add (1)` returns a reference to the `obj`. Through this reference
`add (2)` is called, so on and so forth. The constructor doesn't return
anything so this pattern of calling can't be applied to `B obj;`.

Quote:

this is a const pointer which means that you can change the value of the object it points to, but you can not make it point to something else!

this pointer - C++

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