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operator==,!=,<,<=,>,>=,<=>(std::thread::id) - cppreference.com

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Defined in header <thread>

bool operator==( std::thread::id lhs, std::thread::id rhs ) noexcept;

 (1) (since C++11)

bool operator!=( std::thread::id lhs, std::thread::id rhs ) noexcept;

 (2) (since C++11)
(until C++20)

bool operator< ( std::thread::id lhs, std::thread::id rhs ) noexcept;

 (3) (since C++11)
(until C++20)

bool operator<=( std::thread::id lhs, std::thread::id rhs ) noexcept;

 (4) (since C++11)
(until C++20)

bool operator> ( std::thread::id lhs, std::thread::id rhs ) noexcept;

 (5) (since C++11)
(until C++20)

bool operator>=( std::thread::id lhs, std::thread::id rhs ) noexcept;

 (6) (since C++11)
(until C++20)

std::strong_ordering operator<=>( std::thread::id lhs, std::thread::id rhs ) noexcept;

 (7) (since C++20)

Compares two thread identifiers.

1,2) Checks whether lhs and rhs represent either the same thread, or no thread.

3-7) Compares lhs and rhs in an unspecified total ordering.

The <, <=, >, >=, and != operators are synthesized from operator<=> and operator== respectively.

(since C++20)

Parameters

lhs, rhs - thread identifiers to compare

Return value

1-6) true if the corresponding relation holds, false otherwise.

7) std::strong_ordering::less if lhs is less than rhs in the total ordering; otherwise std::strong_ordering::greater if rhs is less than lhs in the total ordering; otherwise std::strong_ordering::equal.

Complexity

Constant.

Example

#include <cassert>
#include <chrono>
#include <iostream>
#include <thread>


int main()
{
    auto work = [] { std::this_thread::sleep_for(std::chrono::seconds(1)); };
    std::thread t1(work);
    std::thread t2(work);

    assert(t1.get_id() == t1.get_id() and
           t2.get_id() == t2.get_id() and
           t1.get_id() != t2.get_id());

    if (const auto cmp = t1.get_id() <=> t2.get_id(); cmp < 0)
        std::cout << "id1 < id2\n";
    else
        std::cout << "id1 > id2\n";

    std::cout << "id1: " << t1.get_id() << "\n"
                 "id2: " << t2.get_id() << '\n';

    t1.join();
    t2.join();
}

Possible output: 

id1 > id2
id1: 139741717640896
id2: 139741709248192

See also