C++ const_iterator no matching constructor

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!

data is the array of type T containing everything in the list. — Nurder
– Nurder, Commented Sep 10, 2014 at 2:25

PaulMcKenzie · Accepted Answer · 2014-09-10 02:48:24Z

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.

tl;dr just shove const everywhere you could ever need it. This fixed it. Thank you so much!

Neil Kirk · Accepted Answer · 2014-09-10 02:19:26Z

1

const_iterator( T *l) should be const_iterator(const T *l)

answered Sep 10, 2014 at 2:19

Neil Kirk

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1 Comment

Nurder Over a year ago

Tried that, and have reflected it above. Still spits out the same error.

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