const_iterator的初始化程序没有匹配的构造函数

Question

Alright so here's my problem. I'm being told that there is no matching constructor for my class. Here's the code that's calling it. (ignore the inputs. it doesn't seem to matter what I put in, it all comes out bad).

const_iterator end() const { return const_iterator(root->parent,true); }

and here are the initializers.

const_iterator(Node *n, bool b):node(n),end(b) {}
const_iterator(const_iterator &that):node(that.node),end(that.end){}

for the first one, the compiler says that 2 arguments are expected and only one is provided and the second says that an l-value is expected.

Answer 1

Your compiler is trying to find a copy-constructor for const_iterator that can be used to initialize the return value of end() - the issue is not with the return statement itself, but with the copying of the return expression into the return value.

Since you're returning a temporary, you need a copy constructor that can take a temporary ( r-value ). A reference to non-const can't be bound to a temporary, so your second constructor can't be chosen.

On the other hand, a reference to const could match. So since you're not modifying the argument anyway, change your signature:

const_iterator(const_iterator const& that):node(that.node),end(that.end){}

or

const_iterator(const const_iterator& that):node(that.node),end(that.end){}