Why *this returned from a const member function cannot be used to call other functions in C++?

Question

I got the following code:

class Book
{
public:
    void print();
    const Book &Book::get();
};
void Book::print()
{
    cout << "print()" << endl;
}
const Book &Book::get()
{
    cout << "get()" << endl;
    return *this;
}

Then I did:

Book b;
b.get().print(); // This did not work. Why is that?

Answer 1

It can call other functions, but not in this case.

You're returning a const Book & from get() . This is then calling print() , which is a non-const function. To fix this, make print() const:

void print() const;

void Book::print() const
{
    cout << "print()" << endl;
}

This const ensures your object's state will not be changed, which complies with the const object you return from get() . Note that it can change mutable members though, as that's their whole purpose.

Edit: By the way, the term you're looking for is method chaining .

Answer 2

Book :: print（）不是const成员函数，因此不能用Book :: get（）返回的const Book引用调用。