operator==,!=,<,<=,>,>=(std::pair) – cppreference.com

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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.

Parameter

Rückgabewert

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)

Beispiel

#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";
    }
}