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

From cppreference.com
 
 
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
Utilities
(C++20)
Iterator adaptors
Stream iterators
Iterator customization points
Iterator operations
(C++11)
(C++11)
Range access
(C++11)(C++14)
(C++11)(C++14)
(C++17)(C++20)
(C++14)(C++14)
(C++14)(C++14)
(C++17)
(C++17)
 
std::counted_iterator
Member functions
counted_iterator::operator++counted_iterator::operator++(int)counted_iterator::operator+counted_iterator::operator+=counted_iterator::operator--counted_iterator::operator--(int)counted_iterator::operator-counted_iterator::operator-=
(C++20)(C++20)(C++20)(C++20)(C++20)(C++20)(C++20)(C++20)
Non-member functions
(C++20)(C++20)
(C++20)
(C++20)
(C++20)
(C++20)
Helper classes
 
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)

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;.

Contents

[edit] Parameters

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

[edit] 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.

[edit] Example

#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)
}

[edit] See also

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