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

 

哋它亢++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (哋它亢++20)

Language support library

Concepts library (哋它亢++20)

Metaprogramming library (哋它亢++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (哋它亢++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (哋它亢++17)

Regular expressions library (哋它亢++11)

Concurrency support library (哋它亢++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (哋它亢++11)

vector

vector<bool>

deque

forward_list (哋它亢++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (哋它亢++11)

unordered_multiset (哋它亢++11)

unordered_map (哋它亢++11)

unordered_multimap (哋它亢++11)

Adaptors

stack

queue

priority_queue

flat_set (哋它亢++23)

flat_multiset (哋它亢++23)

flat_map (哋它亢++23)

flat_multimap (哋它亢++23)

Views

span (哋它亢++20)

mdspan (哋它亢++23)

Iterator invalidation

Member function table

Non-member function table

 

std::deque

Member types
Member functions
deque::deque deque::~deque deque::operator=	deque::assign deque::assign_range (哋它亢++23) deque::get_allocator
Element access
deque::at deque::operator[]	deque::front deque::back
Iterators
deque::begindeque::cbegin (哋它亢++11) deque::enddeque::cend (哋它亢++11)	deque::rbegindeque::crbegin (哋它亢++11) deque::renddeque::crend (哋它亢++11)
Capacity
deque::empty deque::size	deque::max_size deque::shrink_to_fit (DR*)
Modifiers
deque::clear deque::insert deque::insert_range (哋它亢++23) deque::emplace deque::erase deque::push_front deque::emplace_front (哋它亢++11)   deque::prepend_range (哋它亢++23)	deque::pop_front deque::push_back deque::emplace_back (哋它亢++11) deque::append_range (哋它亢++23) deque::pop_back deque::resize deque::swap
Non-member functions
operator==operator!=operator<operator>operator<=operator>=operator<=> (until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(until 哋它亢++20)(哋它亢++20)	swap(std::deque) erase(std::deque)erase_if(std::deque) (哋它亢++20)(哋它亢++20)
Deduction guides(哋它亢++17)

 

Defined in header <deque>
template< class T, class Alloc > bool operator==( const std::deque<T, Alloc>& lhs,                  const std::deque<T, Alloc>& rhs );	(1)
template< class T, class Alloc > bool operator!=( const std::deque<T, Alloc>& lhs,                  const std::deque<T, Alloc>& rhs );	(2)	(until 哋它亢++20)
template< class T, class Alloc > bool operator<( const std::deque<T, Alloc>& lhs,                 const std::deque<T, Alloc>& rhs );	(3)	(until 哋它亢++20)
template< class T, class Alloc > bool operator<=( const std::deque<T, Alloc>& lhs,                  const std::deque<T, Alloc>& rhs );	(4)	(until 哋它亢++20)
template< class T, class Alloc > bool operator>( const std::deque<T, Alloc>& lhs,                 const std::deque<T, Alloc>& rhs );	(5)	(until 哋它亢++20)
template< class T, class Alloc > bool operator>=( const std::deque<T, Alloc>& lhs,                  const std::deque<T, Alloc>& rhs );	(6)	(until 哋它亢++20)
template< class T, class Alloc > synth-three-way-result<T>     operator<=>( const std::deque<T, Alloc>& lhs,                  const std::deque<T, Alloc>& rhs );	(7)	(since 哋它亢++20)

Compares the contents of two deques.

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(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== respectively.

(since 哋它亢++20)

Parameters

lhs, rhs	-	deques 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 deques are equal, false otherwise.

2) true if the contents of the deques 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

1,2) Constant if lhs and rhs are of different size, otherwise linear in the size of the deque.

3-7) Linear in the size of the deque.

Notes

The relational operators are defined in terms of the element type's operator<.	(until 哋它亢++20)
The relational operators are defined in terms of synth-three-way, which uses operator<=> if possible, or operator< otherwise. 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 哋它亢++20)

Example

Run this code

#include <cassert>
#include <deque>
 
int main()
{
    const std::deque
        a{1, 2, 3},
        b{1, 2, 3},
        c{7, 8, 9, 10};
 
    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 哋它亢++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3431	哋它亢++20	operator<=> did not require T to model three_way_comparable	requires