std::set rend() method

since C++11

// Non const versionreverse_iterator rend() noexcept;// Const versionreverse_iterator rend() const noexcept;// Const versionconst_reverse_iterator crend() const noexcept;

until C++11

// Non const versionreverse_iterator rend();// Const versionconst_reverse_iterator crend();

It corresponds to the last element of the non-reversed container.

Returns a reverse iterator

to the last element of the container. It corresponds to the element preceding the first element of the non-reversed container.

It effectively returns an iterator that points past the end of the original container. Attempting to dereference a past-the-end iterator is undefined behaviour

.

note

This method doesn't actually reverse the container, it just returns an iterator that points to the element before the first element of it, and whose +, -, --, ++ operators have slightly changed implementations.

For example it++ decrements the internal pointer and it-- increments it (so that traversing the container in a reverse order actually works).

If the container is empty, the returned iterator will be equal to rbegin().

Parameters

(none)

Return value

Reverse iterator to the first element.

Complexity

Constant - O(1).

Difference between rend and crend

For a const container c, rend and crend are the same - c.rend() == c.crend()

For non-const container of type c they return different iterators:

Non const container

rend

#include <set>int main(){	std::set<int> set = {1, 2, 3, 4, 5};	auto it = set.rend(); // Type: std::set<int>::reverse_iterator	*std::prev(it) = 5; // ✔ Ok}

crend

#include <set>int main(){	std::set<int> set = {1, 2, 3, 4, 5};	auto it = set.crend(); // Type: std::set<int>::const_reverse_iterator	*std::prev(it) = 5; // ❌ Error! }

Const container

rend

#include <set>int main(){	const std::set<int> set = {1, 2, 3, 4, 5};	auto it = set.rend(); // Type: std::set<int>::const_reverse_iterator	*std::prev(it) = 5; // ❌ Error! }

crend

#include <set>int main(){	const std::set<int> set = {1, 2, 3, 4, 5};	auto it = set.crend(); // Type: std::set<int>::const_reverse_iterator	*std::prev(it) = 5; // ❌ Error! }

Example

Main.cpp

#include <iostream>#include <set> int main(){	std::set<unsigned> rep{1, 2, 3, 4, 1, 2, 3, 4}; 	for (auto it = rep.crbegin(); it != rep.crend(); ++it) {		for (auto n = *it; n > 0; --n)			std::cout << "⏼" << ' ';		std::cout << '\n';	}}

Output

⏼ ⏼ ⏼ ⏼ ⏼ ⏼ ⏼ ⏼ ⏼ ⏼