operator==,!=,<,<=,>,>=,<=>(std::array)

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< cpp‎ | container‎ | array

C++
Containers library
std::array
Defined in header <array>
template < class T, std::size_t N >

bool operator== ( const std::array <T, N> & lhs,

const std::array <T, N> & rhs ) ;
(1) (since C++11)
(constexpr since C++20)
template < class T, std::size_t N >

bool operator! = ( const std::array <T, N> & lhs,

const std::array <T, N> & rhs ) ;
(2) (since C++11)
(until C++20)
template < class T, std::size_t N >

bool operator< ( const std::array <T, N> & lhs,

const std::array <T, N> & rhs ) ;
(3) (since C++11)
(until C++20)
template < class T, std::size_t N >

bool operator<= ( const std::array <T, N> & lhs,

const std::array <T, N> & rhs ) ;
(4) (since C++11)
(until C++20)
template < class T, std::size_t N >

bool operator> ( const std::array <T, N> & lhs,

const std::array <T, N> & rhs ) ;
(5) (since C++11)
(until C++20)
template < class T, std::size_t N >

bool operator>= ( const std::array <T, N> & lhs,

const std::array <T, N> & rhs ) ;
(6) (since C++11)
(until C++20)
template < class T, std::size_t N >

constexpr synth-three-way-result<T>
    operator<=> ( const std::array <T, N> & lhs,

const std::array <T, N> & rhs ) ;
(7) (since C++20)

Compares the contents of two arrays.

1,2) Checks if the contents of lhs and rhs are equal, that is, they have the same number of elements and each element in lhs compares equal with the element in rhs
3-6) Compares the contents of lhs and rhs lexicographically. The comparison is performed by a function equivalent to std::lexicographical_compare
7) Compares the contents of lhs and rhs lexicographically. The comparison is performed as if by calling std::lexicographical_compare_three_way (lhs.begin ( ), lhs.end ( )
rhs.begin(), rhs.end(), synth-three-way )
The return type is the return type of synth-three-way (i.e., synth-three-way-result <T>
If none of the following conditions is satisfied, the behavior is undefined:
  • T models three_way_comparable.
  • < is defined for values of type (possibly const-qualified) T, and < is a total ordering relationship.

The <, <=, >, >=, and != operators are synthesized from operator<=> and operator==

(since C++20)

Parameters

lhs, rhs - arrays whose contents to compare
-
T must meet the requirements of EqualityComparable
-
T must meet the requirements of LessThanComparable

Return value

1) true if the contents of the arrays are equal, false
2) true if the contents of the arrays are not equal, false
3) true if the contents of the lhs are lexicographically less than the contents of rhs, false
4) true if the contents of the lhs are lexicographically less than or equal to the contents of rhs, false
5) true if the contents of the lhs are lexicographically greater than the contents of rhs, false
6) true if the contents of the lhs are lexicographically greater than or equal to the contents of rhs, false
7) The relative order of the first pair of non-equivalent elements in lhs and rhs if there are such elements, lhs.size ( ) <=> rhs.size ( )

Complexity

Linear in the size of the array.

Notes

The relational operators are defined in terms of the element type's operator<.

(until C++20)

The relational operators are defined in terms of synth-three-way, which uses operator<=> if possible, or operator<

Notably, if the element does not itself provide operator<=>, but is implicitly convertible to a three-way comparable type, that conversion will be used instead of operator<

(since C++20)

Example

Run this code
#include <cassert>
#include <compare>
#include <array>
 
int main()
{
    const std::array
        a{1, 2, 3},
        b{1, 2, 3},
        c{7, 8, 9};
 
    assert
    (""
        "Compare equal containers:" &&
        (a != b) == false &&
        (a == b) == true &&
        (a < b) == false &&
        (a <= b) == true &&
        (a > b) == false &&
        (a >= b) == true &&
        (a <=> b) != std::weak_ordering::less &&
        (a <=> b) != std::weak_ordering::greater &&
        (a <=> b) == std::weak_ordering::equivalent &&
        (a <=> b) >= 0 &&
        (a <=> b) <= 0 &&
        (a <=> b) == 0 &&
 
        "Compare non equal containers:" &&
        (a != c) == true &&
        (a == c) == false &&
        (a < c) == true &&
        (a <= c) == true &&
        (a > c) == false &&
        (a >= c) == false &&
        (a <=> c) == std::weak_ordering::less &&
        (a <=> c) != std::weak_ordering::equivalent &&
        (a <=> c) != std::weak_ordering::greater &&
        (a <=> c) < 0 &&
        (a <=> c) != 0 &&
        (a <=> c) <= 0 &&
    "");
}

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 3431 C++20 operator<=> did not require T
to model three_way_comparable 		requires
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