std::string_view rend() method

od C++17

// Const version only
constexpr const iterator rend() const noexcept;

// Const version only
constexpr const_iterator crend() const noexcept;

Returns a reverse iterator

to the last element of the reversed view.

It corresponds to the element preceding the first element of the original view.

Undefined Behavior

Attempting to dereference a past the end iterator is undefined behaviour

.

zanotuj

This method doesn't actually reverse the view, it just returns an iterator that points to the element before the first element of the view, and which +, -, --, ++ 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

Unlike for other containers, like std::string or std::vector, rend and crend both return the same iterator.

Non const container

rend

#include <string_view> 

int main()
{
    std::string_view str = "Hello";
    auto it = str.crend(); // Type: std::string_view::reverse_const_iterator
    *std::prev(it) = 'J'; // ❌ Error! 
}

crend

#include <string_view>

int main()
{
    std::string_view str = "Hello";
    auto it = str.crend(); // Type: std::string_view::reverse_const_iterator
    *std::prev(it) = 'J'; // ❌ Error! 
}

Const container

rend

#include <string_view>

int main()
{
    const std::string_view str = "Hello";
    auto it = str.rend(); // Type: std::string_view::reverse_const_iterator
    *std::prev(it) = 'J'; // ❌ Error! 
}

crend

#include <string_view>

int main()
{
    const std::string_view str = "Hello";
    auto it = str.crend(); // Type: std::string_view::reverse_const_iterator
    *std::prev(it) = 'J'; // ❌ Error! 
}

Example

Main.cpp

#include <algorithm>
#include <iostream>
#include <iterator>
#include <string_view>
 
int main()
{
    std::ostream_iterator<char> out_it(std::cout);
    std::string_view str_view("abcdef");
 
    std::copy(str_view.rbegin(), str_view.rend(), out_it);
    *out_it = '\n';
 
    std::copy(str_view.crbegin(), str_view.crend(), out_it);
    *out_it = '\n';
}

Output

fedcba
fedcba