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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

Views

span (C++20)

 

std::array

Member functions

Element access

array::at

array::operator[]

array::front

array::back

array::data

Iterators

array::beginarray::cbegin

array::endarray::cend

array::rbeginarray::crbegin

array::rendarray::crend

Capacity

array::empty

array::size

array::max_size

Modifiers

array::fill

array::swap

Non-member functions

get

std::swap

to_array (C++20)

operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)

Helper classes

tuple_size

tuple_element

Deduction guides(C++17)

 

Defined in header <array>
	(1)
template< class T, std::size_t N > bool operator==( const std::array<T,N>& lhs,                  const std::array<T,N>& rhs );			(until C++20)
template< class T, std::size_t N > constexpr bool operator==( const std::array<T,N>& lhs,                            const std::array<T,N>& rhs );			(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)	(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)	(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)	(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)	(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)	(until C++20)
template< class T, std::size_t N > constexpr /* see below */ 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 at the same position.

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 on two arrays with a function object performing synthesized three-way comparison (see below). The return type is same as the result type of synthesized three-way comparison.

Given two const E lvalues lhs and rhs as left hand operand and right hand operand respectively (where E is T), synthesized three-way comparison is defined as:

• if std::three_way_comparable_with<E, E> is satisfied, equivalent to lhs <=> rhs;
• otherwise, if comparing two const E lvalues by operator< is well-formed and the result type satisfies boolean-testable, equivalent to

lhs < rhs ? std::weak_ordering::less :
rhs < lhs ? std::weak_ordering::greater :
            std::weak_ordering::equivalent

• otherwise, synthesized three-way comparison is not defined, and operator<=> does not participate in overload resolution.

The behavior of operator<=> is undefined if three_way_comparable_with or boolean-testable is satisfied but not modeled, or operator< is used but E and < do not establish a total order.

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

(since C++20)

Parameters

lhs, rhs	-	arrays whose contents to compare
- T must meet the requirements of EqualityComparable in order to use overloads (1-2).
- T must meet the requirements of LessThanComparable in order to use overloads (3-6). The ordering relation must establish total order.

Return value

1) true if the contents of the arrays are equal, false otherwise

2) true if the contents of the arrays are not equal, false otherwise

3) true if the contents of the lhs are lexicographically less than the contents of rhs, false otherwise

4) true if the contents of the lhs are lexicographically less than or equal to the contents of rhs, false otherwise

5) true if the contents of the lhs are lexicographically greater than the contents of rhs, false otherwise

6) true if the contents of the lhs are lexicographically greater than or equal to the contents of rhs, false otherwise

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() otherwise.

Complexity

Linear in the size of the array

Example

Run this code

#include <iostream>
#include <array>
 
int main()
{
    std::array<int, 3> alice{1, 2, 3};
    std::array<int, 3> bob{7, 8, 9};
    std::array<int, 3> eve{1, 2, 3};
 
    std::cout << std::boolalpha;
 
    // Compare non equal containers
    std::cout << "alice == bob returns " << (alice == bob) << '\n';
    std::cout << "alice != bob returns " << (alice != bob) << '\n';
    std::cout << "alice <  bob returns " << (alice < bob) << '\n';
    std::cout << "alice <= bob returns " << (alice <= bob) << '\n';
    std::cout << "alice >  bob returns " << (alice > bob) << '\n';
    std::cout << "alice >= bob returns " << (alice >= bob) << '\n';
 
    std::cout << '\n';
 
    // Compare equal containers
    std::cout << "alice == eve returns " << (alice == eve) << '\n';
    std::cout << "alice != eve returns " << (alice != eve) << '\n';
    std::cout << "alice <  eve returns " << (alice < eve) << '\n';
    std::cout << "alice <= eve returns " << (alice <= eve) << '\n';
    std::cout << "alice >  eve returns " << (alice > eve) << '\n';
    std::cout << "alice >= eve returns " << (alice >= eve) << '\n';
}

Output:

alice == bob returns false
alice != bob returns true
alice <  bob returns true
alice <= bob returns true
alice >  bob returns false
alice >= bob returns false
 
alice == eve returns true
alice != eve returns false
alice <  eve returns false
alice <= eve returns true
alice >  eve returns false
alice >= eve returns true