std::vector rbegin() method
- since C++11
- until C++11
// Non const version
reverse_iterator rbegin() noexcept;
// Const version
reverse_iterator rbegin() const noexcept;
// Const version
const_reverse_iterator crbegin() const noexcept;
// Non const version
reverse_iterator rbegin();
// Const version
const_reverse_iterator crbegin();
Returns a reverse iterator
to the first element of the reversed vector. It corresponds to the last element of the non-reversed vector.This method doesn't actually reverse the vector, it just returns an iterator that points to the last element of the vector,
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 rend()
.
Parametersโ
(none)
Return valueโ
Reverse iterator to the first element.
Complexityโ
Constant.
Difference between rbegin and crbeginโ
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
- Const container
- rbegin
- crbegin
#include <map>
int main()
{
std::map<int, float> map = { {1, 1.f}, {2, 3.f}, {5, 8.f} };
auto it = map.rbegin(); // Type: std::map<int, float>::reverse_iterator
*it = 5; // โ Ok
}
#include <map>
int main()
{
std::map<int, float> map = { {1, 1.f}, {2, 3.f}, {5, 8.f} };
auto it = map.crbegin(); // Type: std::map<int, float>::reverse_const_iterator
*it = 5; // โ Error!
}
- rbegin
- crbegin
#include <map>
int main()
{
const std::map<int, float> map = { {1, 1.f}, {2, 3.f}, {5, 8.f} };
auto it = map.rbegin(); // Type: std::map<int, float>::reverse_const_iterator
*it = 5; // โ Error!
}
#include <map>
int main()
{
const std::map<int, float> map = { {1, 1.f}, {2, 3.f}, {5, 8.f} };
auto it = map.crbegin(); // Type: std::map<int, float>::reverse_const_iterator
*it = 5; // โ Error!
}
Exampleโ
#include <iomanip>
#include <iostream>
#include <map>
#include <string_view>
int main()
{
const std::map<int, std::string_view> coins {
{10, "dime"},
{100, "dollar"},
{50, "half dollar"},
{5, "nickel"},
{1, "penny"},
{25, "quarter"}
}; // initializer entries in name alphabetical order
std::cout << "US coins in circulation, largest to smallest denomination:\n";
for (auto it = coins.crbegin(); it != coins.crend(); ++it) {
std::cout << std::setw(11) << it->second << " = ยข" << it->first << '\n';
}
}
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