std::vector iterator as a class member

Question

I am puzzled by the behaviour of the following code.

I have a dummy class with a vector member. I would also like an iterator member so I can access the vector in the various methods without having to declare a new one each time. It seems OK until I introduce a const method.

The test1 method uses the vector and the iterator members just fine.

The test2 method throws a compile error when I try to use the const_iterator member with the vector. However, if I declare a new const_iterator in the method it compiles.

Can someone please explain this behaviour.

Thanks

class dummy {
    public:
        std::vector<double> data;
        // Declare iterators as members
        std::vector<double>::iterator iterator1;
        std::vector<double>::const_iterator const_iterator1;

        void test1(){
            iterator1 = data.begin();
        }

        void test2() const {
             // const_iterator1 = data.begin(); // Fails
            std::vector<double>::const_iterator const_iterator2 = data.begin(); // Compiles
        }
};

Abhishek Bansal Abhishek Bansal · Accepted Answer · 2014-01-14T13:58:52

You cannot change values of member variables in a const function.

const_iterator1 = data.begin(); // Changes the value of const_iterator1 member variable

std::vector iterator as a class member

1 Answers