C ++ const_iterator没有匹配的构造函数

Question

I'm trying to build a custom const_iterator nested class for my Array-based list class. here's the class

class const_iterator {
private:
   const T *p;
public:
    const_iterator(const T *l) {
        p = l;
    }
    const_iterator(const_iterator &ci) { p=ci.p;}
    const T &operator*() const {return *p;}
    bool operator==(const iterator &i) const {
        if(*p==*i)
            return true;
        else
            return false;
    }
    bool operator!=(const_iterator &i) const {
        if(*p!=*i)
            return true;
        else
            return false;
    }
    const_iterator &operator=(const_iterator &i) const {
        p=i.p;
        return this;
    }
    const_iterator &operator++() const {
        return const_iterator(p+1);
    }
    const_iterator &operator--() const {
        return const_iterator(p-1);
    }

    const_iterator operator++(int) const {
        p = p+1;
        return const_iterator(p-1);
    };
    const_iterator operator--(int) const {
        p=p-1;
        return const_iterator(p+1);
    }

};

However, when I go back into my class to make a begin, end, etc. as shown here:

iterator begin() {
    return iterator(&data[0]);
}
const_iterator begin() const {
    return const_iterator(&data[0]);
}
iterator end() {return iterator(&data[place+1]);}
const_iterator end() const {return const_iterator(&data[place+1]);}

const_iterator cbegin() const {
    return const_iterator(&data[0]);
}
const_iterator cend() const {return const_iterator(&data[place+1]);}

I get an error: "no matching constructor for initialization of 'ArrayList::const_iterator" on my cbegin and cend. I'm aware it's probably something stupid I don't understand about C++. Thanks in advance for the help!

Answer 1

Either remove the const_iterator copy constructor (as it is not needed), or make the copy constructor take a const const_iterator& .

Here is a minimal example:

template <typename T>
class ArrayList
{
    public:
        class const_iterator {
        private:
            const T *p;
        public:
            const_iterator(const T *l) {
                p = l;
            }
            const_iterator(const const_iterator &ci) : p(ci.p) {}
        };

        T data[10];

        const_iterator cbegin() const {
            return const_iterator(&data[0]);
    }
};

int main()
{
    ArrayList<int> a;
    ArrayList<int>::const_iterator it = a.cbegin();
}

This compiles here: http://ideone.com/04EE4P

The removal of the copy constructor also compiles with no errors. This indicates that your user-defined copy constructor that takes a non-const reference was causing the issue.

Answer 2

const_iterator( T *l)应该是const_iterator(const T *l)