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std::reverse_iterator<Iter>::reverse_iterator - cppreference.com

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reverse_iterator();

 (1) (constexpr since C++17)

explicit reverse_iterator( iterator_type x );

 (2) (constexpr since C++17)

template< class U > reverse_iterator( const reverse_iterator<U>& other );

 (3) (constexpr since C++17)

Constructs a new reverse_iterator.

 Overload  current
(1) value-initialized
(2) initialized with x
(3)  initialized with other.current 

3) The converting constructor.

This overload participates in overload resolution only if std::is_same_v<U, Iter> is false and std::convertible_to<const U&, Iter> is modeled.

(since C++20)

Parameters

x - iterator to adapt
other - iterator adaptor to copy

Example

#include <cassert>
#include <concepts>
#include <iterator>
#include <vector>

int main()
{
    std::vector v{0, 1, 2, 3, 4};

    using ReverseIt = std::reverse_iterator<std::vector<int>::const_iterator>;

    ReverseIt i1; // overload (1)
    i1 = v.crbegin();
    assert(*i1 == 4);

    ReverseIt i2(i1); // overload (2)
    assert(i2[0] == 4);

    int x[]{1, 2, 3};
    auto i3 = std::reverse_iterator<int*>(x + std::size(x)); // overload (1)
    i3[0] = -3;
    assert(x[2] == -3);
    std::reverse_iterator<int const*> i4(i3); // overload (3): int => const int
    static_assert(std::convertible_to<decltype(i3)::value_type,
                                      decltype(i4)::value_type>);
    // i4[0] = 5; // Error: assignment of read-only location
}

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 235 C++98 the effect of overload (1) was not specified specified
LWG 1012 C++98 overload (1) default-initialized current it is value-initialized
LWG 3435 C++20 overload (3) was not constrained constrained

See also