std::reverse_iterator<Iter>::operator[]
From cppreference.com
< cpp | iterator | reverse iterator
/* unspecified */ operator[]( difference_type n ) const; |
(until C++17) | |
constexpr /* unspecified */ operator[]( difference_type n ) const; |
(since C++17) | |
Returns a reference to the element at specified relative location.
Parameters
n | - | position relative to current location |
Return value
A reference to the element at relative location, that is, base()[-n - 1].
Notes
The return type is unspecified because the return type of the underlying iterator's operator[] is also unspecified (see LegacyRandomAccessIterator).
Example
Run this code
#include <array> #include <cstddef> #include <iostream> #include <iterator> #include <list> #include <vector> int main() { int a[]{0, 1, 2, 3}; std::reverse_iterator<int*> iter1{std::rbegin(a)}; for (std::size_t i{}; i != std::size(a); ++i) std::cout << iter1[i] << ' '; // decltype(iter1[i]) is `int&` std::cout << '\n'; std::vector v{0, 1, 2, 3}; std::reverse_iterator<std::vector<int>::iterator> iter2{std::rbegin(v)}; for (std::size_t i{}; i != std::size(v); ++i) std::cout << iter2[i] << ' '; // decltype(iter2[i]) is `int&` std::cout << '\n'; // constexpr context constexpr static std::array<int, 4> z{0, 1, 2, 3}; constexpr std::reverse_iterator<decltype(z)::const_iterator> iter3{std::crbegin(z)}; static_assert(iter3[1] == 2); std::list li{0, 1, 2, 3}; std::reverse_iterator<std::list<int>::iterator> iter4{std::rbegin(li)}; *iter4 = 42; // OK // iter4[0] = 13; // compilation error: the underlying iterator // does not model the random access iterator }
Output:
3 2 1 0 3 2 1 0
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 386 | C++98 | the return type was reference
|
made unspecified |
See also
accesses the pointed-to element (public member function) |