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operator==,!=,<,<=,>,>=,<=>(std::move_iterator) - cppreference.com

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Defined in header <iterator>

template< class Iter1, class Iter2 > bool operator==( const std::move_iterator<Iter1>& lhs, const std::move_iterator<Iter2>& rhs );

 (1) (constexpr since C++17)

template< class Iter1, class Iter2 > bool operator!=( const std::move_iterator<Iter1>& lhs, const std::move_iterator<Iter2>& rhs );

 (2) (constexpr since C++17)
(until C++20)

template< class Iter1, class Iter2 > bool operator< ( const std::move_iterator<Iter1>& lhs, const std::move_iterator<Iter2>& rhs );

 (3) (constexpr since C++17)

template< class Iter1, class Iter2 > bool operator<=( const std::move_iterator<Iter1>& lhs, const std::move_iterator<Iter2>& rhs );

 (4) (constexpr since C++17)

template< class Iter1, class Iter2 > bool operator> ( const std::move_iterator<Iter1>& lhs, const std::move_iterator<Iter2>& rhs );

 (5) (constexpr since C++17)

template< class Iter1, class Iter2 > bool operator>=( const std::move_iterator<Iter1>& lhs, const std::move_iterator<Iter2>& rhs );

 (6) (constexpr since C++17)

template< class Iter1, std::three_way_comparable_with<Iter1> Iter2 > constexpr std::compare_three_way_result_t<Iter1, Iter2> operator<=>( const std::move_iterator<Iter1>& lhs, const std::move_iterator<Iter2>& rhs );

 (7) (since C++20)

Compares the underlying iterators of lhs and rhs.

1) This overload participates in overload resolution only if lhs.base() == rhs.base() is well-formed and convertible to bool.

3-6) These overloads participate in overload resolution only if lhs.base() < rhs.base() is well-formed and convertible to bool.

The != operator is synthesized from operator==.

(since C++20)

Parameters

lhs, rhs - iterator adaptors to compare

Return value

1) lhs.base() == rhs.base()

2) !(lhs == rhs)

3) lhs.base() < rhs.base()

4) !(rhs < lhs)

5) rhs < lhs

6) !(lhs < rhs)

7) lhs.base() <=> rhs.base()

Example

#include <cassert>
#include <iterator>

int main()
{
    int a[]{9, 8, 7, 6};
    //            │  └───── x, y
    //            └──────── z

    // “x” and “y” are equal, but “x” is greater than “z”
    std::move_iterator<int*>
        x{std::end(a) - 1},
        y{std::end(a) - 1},
        z{std::end(a) - 2};

    // two-way comparisons
    assert(  x == y );
    assert(!(x != y));
    assert(!(x <  y));
    assert(  x <= y );
    assert(!(x == z));
    assert(  x != z );
    assert(!(x <  z));
    assert(!(x <= z));

    // three-way comparisons
    assert(  x <=> y == 0 );
    assert(!(x <=> y <  0));
    assert(!(x <=> y >  0));
    assert(!(x <=> z == 0));
    assert(!(x <=> z <  0));
    assert(  x <=> z >  0 );
}

See also