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

Defined in header `<utility>`
template< class T1, class T2 > bool operator==( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(1)	(until C++14)
template< class T1, class T2 > constexpr bool operator==( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(1)	(since C++14)
template< class T1, class T2 > bool operator!=( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(2)	(until C++14)
template< class T1, class T2 > constexpr bool operator!=( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(2)	(since C++14)
template< class T1, class T2 > bool operator<( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(3)	(until C++14)
template< class T1, class T2 > constexpr bool operator<( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(3)	(since C++14)
template< class T1, class T2 > bool operator<=( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(4)	(until C++14)
template< class T1, class T2 > constexpr bool operator<=( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(4)	(since C++14)
template< class T1, class T2 > bool operator>( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(5)	(until C++14)
template< class T1, class T2 > constexpr bool operator>( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(5)	(since C++14)
template< class T1, class T2 > bool operator>=( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(6)	(until C++14)
template< class T1, class T2 > constexpr bool operator>=( const pair<T1,T2>& lhs, const pair<T1,T2>& rhs );	(6)	(since C++14)

1-2) Tests if both elements of lhs and rhs are equal, that is, compares lhs.first with rhs.first and lhs.second with rhs.second

3-6) Compares lhs and rhs lexicographically, that is, compares the first elements and only if they are equivalent, compares the second elements.

Parameters

lhs, rhs

-

pairs to compare

Return value

1) true if both lhs.first == rhs.first and lhs.second == rhs.second, otherwise false

2) !(lhs == rhs)

3) If lhs.first<rhs.first, returns true. Otherwise, if rhs.first<lhs.first, returns false. Otherwise, if lhs.second<rhs.second, returns true. Otherwise, returns false.

4) !(rhs < lhs)

5) rhs < lhs

6) !(lhs < rhs)

Example

Because operator< is defined for pairs, containers of pairs can be sorted.

Run this code

#include <iostream>
#include <utility>
#include <vector>
#include <algorithm>
#include <string>

int main()
{
    std::vector<std::pair<int, std::string>> v = { {2, "baz"},
                                                   {2, "bar"},
                                                   {1, "foo"} };
    std::sort(v.begin(), v.end());

    for(auto p: v) {
        std::cout << "(" << p.first << "," << p.second << ")\n";
    }
}

Output:

(1,foo)
(2,bar)
(2,baz)

Language
Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications

Member functions
pair::pair
pair::operator=
pair::swap
Non-member functions
make_pair
operator==operator!=operator<operator<=operator>operator>=
std::swap
get (C++11)
Deduction guides(C++17)
Helper classes
tuple_size (C++11)
tuple_element (C++11)