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) true
if either lhs.firstĀ != rhs.first
or lhs.secondĀ != 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> #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)
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