*this vs this in C++

问题:

I understand what this does, but what is the difference between *this and this?

Yes, I have Googled and read over *this in my text book, but I just don't get it...

回答1:

this is a pointer, and *this is a dereferenced pointer.

If you had a function that returned this, it would be a pointer to the current object, while a function that returned *this would be a "clone" of the current object, allocated on the stack -- unless you have specified the return type of the method to return a reference.

A simple program that shows the difference between operating on copies and references:

#include <iostream>

class Foo
{
    public:
        Foo()
        {
            this->value = 0;
        }

        Foo get_copy()
        {
            return *this;
        }

        Foo& get_copy_as_reference()
        {
            return *this;
        }

        Foo* get_pointer()
        {
            return this;
        }

        void increment()
        {
            this->value++;
        }

        void print_value()
        {
            std::cout << this->value << std::endl;
        }

    private:
        int value;
};

int main()
{
    Foo foo;
    foo.increment();
    foo.print_value();

    foo.get_copy().increment();
    foo.print_value();

    foo.get_copy_as_reference().increment();
    foo.print_value();

    foo.get_pointer()->increment();
    foo.print_value();

    return 0;
}

Output:

1
1
2
3

You can see that when we operate on a copy of our local object, the changes don't persist (because it's a different object entirely), but operating on a reference or pointer does persist the changes.

回答2:

this is a pointer to the instance of the class. *this is a reference to the same. They are different in the same way that int* i_ptr and int& i_ref are different.

回答3:

There is no real difference, this->foo() is the same as (*this).foo().