std::string rbegin() method

od C++20

// Non-const version
constexpr iterator end() noexcept;

// Const version
constexpr const_iterator end() const noexcept;
constexpr const_iterator cend() const noexcept;

od C++11

// Non-const version
iterator end() noexcept;

// Const version
const_iterator end() const noexcept;
const_iterator cend() const noexcept;

do C++11

// Non-const version
iterator end();

// Const version
const_iterator end() const;

Returns a reverse iterator

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

zanotuj

This method doesn't actually reverse the string, it returns an iterator that points to the last element of the string, 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 rend().

Parameters

(none)

Return value

Reverse iterator to the first element.

Complexity

Constant - O(1)..

Difference between rbegin and crbegin

For a const container c, rbegin and crbegin are the same - c.rbegin() == c.crbegin()

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

Non const container

rbegin

#include <string>

int main()
{
    std::string str = "Hello";
    auto it = str.rbegin(); // Type: std::string::reverse_iterator
    *it = 'J'; // ✔ Ok
}

crbegin

#include <string>

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

Const container

rbegin

#include <string>

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

crbegin

#include <string>

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

Example

Main.cpp

#include <iostream>
#include <algorithm>
#include <iterator>
#include <string>
 
int main()
{
    std::string s("Exemplar!");
    *s.rbegin() = 'y';
    std::cout << s << '\n'; // "Exemplary"
 
    std::string c;
    std::copy(s.crbegin(), s.crend(), std::back_inserter(c));
    std::cout << c << '\n'; // "yralpmexE"
}

Output

Exemplary
yralpmexE