operator- (std::counted_iterator)

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C++
Iterator library
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(C++20)
(C++20)
(C++20)
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(C++20)
Iterator adaptors
Range access
(C++11) (C++14)
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(C++14) (C++14)
(C++17) (C++20)
(C++17)
(C++17)
std::counted_iterator
template < std:: common_with < I > I2 >

friend constexpr std:: iter_difference_t < I2 > operator - (

const counted_iterator & x, const counted_iterator < I2 > & y ) ;
(since C++20)

Computes the distance between two iterator adaptors.

The behavior is undefined if x and y do not point to elements of the same sequence. That is, there must exist some n such that std:: next ( x. base ( ) , x. count ( ) + n ) and std:: next ( y. base ( ) , y. count ( ) + n ) refer to the same element.

This function template is not visible to ordinary unqualified or qualified lookup , and can only be found by argument-dependent lookup when std::counted_iterator<I> is an associated class of the arguments.

Parameters

x, y - iterator adaptors to compute the difference of

Return value

y. count ( ) - x. count ( )

Notes

Since the length counts down, not up, the order of the arguments of operator - in the underlying expression is reversed, i.e. y is lhs and x is rhs .

Example

Run this code 
#include <initializer_list>
#include <iterator>
 
int main()
{
    static constexpr auto v = {1, 2, 3, 4, 5, 6};
    constexpr std::counted_iterator<std::initializer_list<int>::iterator>
        it1{v.begin(), 5},
        it2{it1 + 3},
        it3{v.begin(), 2};
 
    static_assert(it1 - it2 == -3);
    static_assert(it2 - it1 == +3);
//  static_assert(it1 - it3 == -3); // UB: operands of operator- do not refer to
                                    // elements of the same sequence
}

See also

(C++20)
advances or decrements the iterator
(public member function)
(C++20)
advances the iterator
(function template)
(C++20)
computes the signed distance to the end
(function template)
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