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

 

C++

Language

Concepts

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)

 

Utilities library

Type support (basic types, RTTI, type traits)

Dynamic memory management

Error handling

Program utilities

Variadic functions

Date and time

Function objects

initializer_list (C++11)

bitset

hash (C++11)

Relational operators

rel_ops::operator!= rel_ops::operator> rel_ops::operator<= rel_ops::operator>=

Pairs and tuples

pair

tuple (C++11)

piecewise_construct_t (C++11)

piecewise_construct (C++11)

Swap, forward and move

swap

forward (C++11)

move (C++11)

move_if_noexcept (C++11)

declval (C++11)

 

std::pair

Member functions

pair::pair

pair::operator=

pair::swap

Non-member functions

make_pair

operator= operator!= operator< operator<= operator> operator>=

std::swap

get (C++11)

Helper classes

tuple_size (C++11)

tuple_element (C++11)

 

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

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) true if either lhs.first != rhs.first or lhs.second != rhs.second, otherwise false

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.

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