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    std::counted_iterator<I>::operator++,+,+=,--,-,-=

    From cppreference.com
     
    C++
     
    Iterator library
    Iterator concepts
    Iterator primitives
    Algorithm concepts and utilities
    Indirect callable concepts
    Common algorithm requirements
    (C++20)
    (C++20)
    (C++20)
    Utilities
    (C++20)
    Iterator adaptors
    Range access
    (C++11)(C++14)
    (C++14)(C++14)  
    (C++11)(C++14)
    (C++14)(C++14)  
    (C++17)(C++20)
    (C++17)
    (C++17)
     
    std::counted_iterator
     
    constexpr counted_iterator& operator++();
    		 (1) (since C++20)
    constexpr decltype(auto) operator++( int );
    		 (2) (since C++20)
    constexpr counted_iterator operator++( int ) requires std::forward_iterator<I>;
    		 (3) (since C++20)
    constexpr counted_iterator& operator--() requires std::bidirectional_iterator<I>;
    		 (4) (since C++20)
    constexpr counted_iterator operator--( int ) requires std::bidirectional_iterator<I>;
    		 (5) (since C++20)
    constexpr counted_iterator operator+( std::iter_difference_t<I> n ) const requires std::random_access_iterator<I>;
    		 (6) (since C++20)
    constexpr counted_iterator& operator+=( std::iter_difference_t<I> n ) requires std::random_access_iterator<I>;
    		 (7) (since C++20)
    constexpr counted_iterator operator-( std::iter_difference_t<I> n ) const requires std::random_access_iterator<I>;
    		 (8) (since C++20)
    constexpr counted_iterator& operator-=( std::iter_difference_t<I> n ) requires std::random_access_iterator<I>;
    		 (9) (since C++20)
    See More

    Increments or decrements the underlying iterator current and the distance to the end length.

    The behavior of these functions is undefined if the length would be set to a minus value.

    1) Pre-increments by one. Equivalent to ++current; --length; return *this;.
    2) Post-increments by one. Equivalent to --length; try { return current++; } catch(...) { ++length; throw; }.
    3) Post-increments by one. Equivalent to counted_iterator temp{*this}; ++*this; return temp;.
    4) Pre-decrements by one. Equivalent to --current; ++length; return *this;.
    5) Post-decrements by one. Equivalent to counted_iterator temp{*this}; --*this; return temp;.
    6) Returns an iterator adaptor which is advanced by n. Equivalent to return counted_iterator(current + n, length - n);.
    7) Advances the iterator adaptor by n. Equivalent to current += n; length -= n; return *this;.
    8) Returns an iterator adaptor which is advanced by -n. Equivalent to return counted_iterator(current - n, length + n);.
    9) Advances the iterator adaptor by -n. Equivalent to current -= n; length += n; return *this;.

    Parameters

    n - the number of positions to increment or decrement the iterator adaptor

    Return value

    1) *this
    2,3) A copy of *this that was made before the change.
    4) *this
    5) A copy of *this that was made before the change.
    6) An iterator adaptor which is advanced by n.
    7) *this
    8) An iterator adaptor which is advanced by -n.
    9) *this

    Example

    Run this code
    #include <cassert>
#include <initializer_list>
#include <iterator>

int main()
{
    const auto v = {1, 2, 3, 4, 5, 6};
    std::counted_iterator<std::initializer_list<int>::iterator> it1{v.begin(), 5};

    ++it1;              assert(*it1 == 2 && it1.count() == 4); // (1)
    auto it2 = it1++;   assert(*it2 == 2 && *it1 == 3);        // (3)
    --it1;              assert(*it1 == 2 && it1.count() == 4); // (4)
    auto it3 = it1--;   assert(*it3 == 2 && *it1 == 1);        // (5)
    auto it4 = it1 + 3; assert(*it4 == 4 && it4.count() == 2); // (6)
    auto it5 = it4 - 3; assert(*it5 == 1 && it5.count() == 5); // (8)
    it1 += 3;           assert(*it1 == 4 && it1.count() == 2); // (7)
    it1 -= 3;           assert(*it1 == 1 && it1.count() == 5); // (9)
}

    See also

    (C++20)
    		 advances the iterator
    (function template) [edit]
    (C++20)
    		 computes the distance between two iterator adaptors
    (function template) [edit]