operator==,!=,<,<=,>,>=,<=>(std::reverse_iterator)
| (1) | |
template< class Iterator1, class Iterator2 >
bool operator==( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (until C++17) |
template< class Iterator1, class Iterator2 >
constexpr bool operator==( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (since C++17) |
| (2) | |
template< class Iterator1, class Iterator2 >
bool operator!=( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (until C++17) |
template< class Iterator1, class Iterator2 >
constexpr bool operator!=( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (since C++17) |
| (3) | |
template< class Iterator1, class Iterator2 >
bool operator<( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (until C++17) |
template< class Iterator1, class Iterator2 >
constexpr bool operator<( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (since C++17) |
| (4) | |
template< class Iterator1, class Iterator2 >
bool operator<=( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (until C++17) |
template< class Iterator1, class Iterator2 >
constexpr bool operator<=( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (since C++17) |
| (5) | |
template< class Iterator1, class Iterator2 >
bool operator>( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (until C++17) |
template< class Iterator1, class Iterator2 >
constexpr bool operator>( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (since C++17) |
| (6) | |
template< class Iterator1, class Iterator2 >
bool operator>=( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (until C++17) |
template< class Iterator1, class Iterator2 >
constexpr bool operator>=( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (since C++17) |
template< class Iterator1, std::three_way_comparable_with<Iterator1> Iterator2 >
constexpr std::compare_three_way_result_t<Iterator1, Iterator2>
operator<=>( const std::reverse_iterator<Iterator1>& lhs,
const std::reverse_iterator<Iterator2>& rhs );
| (7) | (since C++20) |
Compares the underlying iterators. Inverse comparisons are applied in order to take into account that the iterator order is reversed.
(1-6) only participate in overload resolution if their underlying comparison expressions (see below) are well-formed and convertible to bool .
| (since C++20) |
Parameters
lhs, rhs | - | iterator adaptors to compare |
Return Value
1) lhs.base() == rhs.base()
2) lhs.base() != rhs.base()
3) lhs.base() > rhs.base()
4) lhs.base() >= rhs.base()
5) lhs.base() < rhs.base()
6) lhs.base() <= rhs.base()
7) rhs.base() <=> lhs.base()
Example
#include <compare>
#include <iostream>
#include <iterator>
int main()
{
int a[]{0, 1, 2, 3};
std::reverse_iterator<int*>
x {std::rend(a) - std::size(a)},
y {std::rend(a) - std::size(a)},
z {std::rbegin(a) + 1};
std::cout
<< std::boolalpha
<< "*x == " << *x << '\n'
<< "*y == " << *y << '\n'
<< "*z == " << *z << '\n'
<< "x == y ? " << (x == y) << '\n'
<< "x != y ? " << (x != y) << '\n'
<< "x < y ? " << (x < y) << '\n'
<< "x <= y ? " << (x <= y) << '\n'
<< "x == z ? " << (x == z) << '\n'
<< "x != z ? " << (x != z) << '\n'
<< "x < z ? " << (x < z) << '\n'
<< "x <= z ? " << (x <= z) << '\n'
<< "x <=> y == 0 ? " << (x <=> y == 0) << '\n'
<< "x <=> y < 0 ? " << (x <=> y < 0) << '\n'
<< "x <=> y > 0 ? " << (x <=> y > 0) << '\n'
<< "x <=> z == 0 ? " << (x <=> z == 0) << '\n'
<< "x <=> z < 0 ? " << (x <=> z < 0) << '\n'
<< "x <=> z > 0 ? " << (x <=> z > 0) << '\n'
;
}
Output:
*x == 3
*y == 3
*z == 2
x == y ? true
x != y ? false
x < y ? false
x <= y ? false
x == z ? false
x != z ? true
x < z ? true
x <= z ? true
x <=> y == 0 ? true
x <=> y < 0 ? false
x <=> y > 0 ? false
x <=> z == 0 ? false
x <=> z < 0 ? true
x <=> z > 0 ? false
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 | an std::reverse_iterator could only compare with another
std::reverse_iterator with the same underlying iterator type | allowed comparisons of std::reverse_iterator with different underlying iterator types |