jameshelou - 7 months ago 49

C++ Question

Having trouble understanding the below code:

`int data[5] = { 1, 5, 2, 4, 3 };`

vector<int> X(data, data+5);

int v1 = *max_element(X.begin(), X.end()); // Returns value of max element in vector

int i1 = min_element(X.begin(), X.end()) – X.begin(); // Returns index of min element in vector

Not really sure how subtracting the iterator returned by X.begin returns the index of the max/min element?

Answer

`std::vector<T>::iterator`

satisfies the RandomAccessIterator concept, which means that it has an `operator-`

that allows you to subtract two iterators and obtain a `std::vector<T>::iterator::difference_type`

that indicates the distance between the two iterators.

An under-the-hood implementation for `std::vector<T>::iterator`

could in fact be made using pointers as iterators, in which case the subtraction operator would just be doing pointer arithmetic. There's no *requirement* for the iterator to be implemented using pointers, but it's a potential design.

Other containers' iterators may not have this capability. For instance, `std::set<T>::iterator`

only satisfies the BidirectionalIterator concept, which specifies a less-rich set of functionality than the RandomAccessIterator concept.