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operator-(std::reverse_iterator)

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< cpp‎ | iterator‎ | reverse iterator

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std::reverse_iterator

Member functions

reverse_iterator::reverse_iterator

reverse_iterator::operator=

reverse_iterator::base

reverse_iterator::operator*reverse_iterator::operator->

reverse_iterator::operator[]

reverse_iterator::operator++reverse_iterator::operator+reverse_iterator::operator+=reverse_iterator::operator--reverse_iterator::operator-reverse_iterator::operator-=

Non-member functions

operator==operator!=operator<operator<=operator>operator>=operator<=>

(C++20)

operator-

(C++20)

(C++20)

make_reverse_iterator

(C++14)

Defined in header <iterator>

template< class Iter1, class Iter2 >

typename reverse_iterator<Iter>::difference_type
operator-( const reverse_iterator<Iter1>& lhs,

const reverse_iterator<Iter2>& rhs );

(until C++11)

template< class Iter1, class Iter2 >

auto operator-( const reverse_iterator<Iter1>& lhs,
const reverse_iterator<Iter2>& rhs )

-> decltype(rhs.base() - lhs.base());

(since C++11)
(constexpr since C++17)

Returns the distance between two iterator adaptors.

Contents

[edit] Parameters

lhs, rhs - iterator adaptors to compute the difference of

[edit] Return value

rhs.base() - lhs.base()

[edit] Notes

operator- returns rhs.base() - lhs.base() rather than lhs.base() - rhs.base() because this is a reverse iterator.

[edit] Example

Run this code

#include <iostream>
#include <iterator>
#include <list>
#include <vector>
 
int main()
{
 std::vector vec{0, 1, 2, 3};
 std::reverse_iterator <std::vector <int>::iterator>
 vec_ri1{std::reverse_iterator {vec.rbegin()}},
 vec_ri2{std::reverse_iterator {vec.rend()}};
 std::cout << (vec_ri2 - vec_ri1) << ' '; // 4
 std::cout << (vec_ri1 - vec_ri2) << '\n'; // -4
 
 std::list lst{5, 6, 7, 8};
 std::reverse_iterator <std::list <int>::iterator>
 lst_ri1{std::reverse_iterator {lst.rbegin()}},
 lst_ri2{std::reverse_iterator {lst.rend()}};
// auto n = (lst_ri1 - lst_ri2); // Error: the underlying iterators do not
 // model random access iterator
}

Output:

4 -4

[edit] 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 280	C++98	heterogeneous subtraction was not allowed	allowed

[edit] See also

operator++operator++(int)operator+=operator+operator--operator--(int)operator-=operator-

advances or decrements the reverse_iterator
(public member function) [edit]

advances the iterator
(function template) [edit]

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