Example
Parameters of these operators are lhs and rhs
operator==tests if both elements onlhsandrhspair are equal. The return value istrueif bothlhs.first == rhs.firstANDlhs.second == rhs.second, otherwisefalse
std::pair<int, int> p1 = std::make_pair(1, 2);
std::pair<int, int> p2 = std::make_pair(2, 2);
if (p1 == p2)
std::cout << "equals";
else
std::cout << "not equal"//statement will show this, because they are not identical
-
operator!=tests if any elements onlhsandrhspair are not equal. The return value istrueif eitherlhs.first != rhs.firstORlhs.second != rhs.second, otherwise returnfalse. -
operator<tests iflhs.first<rhs.first, returnstrue. Otherwise, ifrhs.first<lhs.firstreturnsfalse. Otherwise, iflhs.second<rhs.secondreturnstrue, otherwise, returnsfalse. -
operator<=returns!(rhs<lhs) -
operator>returnsrhs<lhs -
operator>=returns!(lhs<rhs)Another example with containers of pairs. It uses
operator<because it needs to sort container.
#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(const auto& p: v) {
std::cout << "(" << p.first << "," << p.second << ") ";
//output: (1,foo) (2,bar) (2,baz)
}
}
