const vector of iterators in c++

Question

If I have a vector that contains iterators of another vector.

For example :

vector<vector<int>::iterator> vec;

what happens when passing this vector in const refrence?

For example:

void fun(const vector<vector<int>::iterator> &vec);

Are the elements of vec inside function fun const_iterator or iterator? can they be modified

Thanks in advance!

Answer 1

No, they aren't const_iterator . Chiefly because const_iterator is a user defined type that is related to iterator via a user defined conversion, and not in fact a const qualified iterator . ⁽¹⁾

What you access inside the function through the vector are const iterator& .

So you can use those to modify the elements referred by them.

The best analogy to this is that const_iterator is to iterator , what const T* is to T* . And what you have inside your function is akin to T * const .

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_{(1) On paper, that is. For vectors it may very well be plain pointers in optimized code. In which case the analogy becomes the reality.}