std::thread::joinable(3)

NAME
std::thread::joinable - std::thread::joinable

Synopsis
   bool joinable() const noexcept; (since C++11)
   Checks if the std::thread object identifies an active thread of execution.
   Specifically, returns true if get_id() != std::thread::id(). So a default
   constructed thread is not joinable.
   A thread that has finished executing code, but has not yet been joined is still
   considered an active thread of execution and is therefore joinable.

Parameters
   (none)

Return value
   true if the thread object identifies an active thread of execution, false otherwise.

Example
// Run this code
 #include <chrono>
 #include <iostream>
 #include <thread>
 using namespace std::chrono_literals;
 void foo()
 {
     std::this_thread::sleep_for(500ms);
 }
 int main()
 {
     std::cout << std::boolalpha;
     std::thread t;
     std::cout << "before starting, joinable: " << t.joinable() << '\n';
     t = std::thread{foo};
     std::cout << "after starting, joinable: " << t.joinable() << '\n';
     t.join();
     std::cout << "after joining, joinable: " << t.joinable() << '\n';
     t = std::thread{foo};
     t.detach();
     std::cout << "after detaching, joinable: " << t.joinable() << '\n';
     std::this_thread::sleep_for(1500ms);
 }

Output:
 before starting, joinable: false
 after starting, joinable: true
 after joining, joinable: false
 after detaching, joinable: false

References
     * C++23 standard (ISO/IEC 14882:2023):
     * 33.4.3.6 Members [thread.thread.member]
     * C++20 standard (ISO/IEC 14882:2020):
     * 32.4.2.5 Members [thread.thread.member]
     * C++17 standard (ISO/IEC 14882:2017):
     * 33.3.2.5 thread members [thread.thread.member]
     * C++14 standard (ISO/IEC 14882:2014):
     * 30.3.1.5 thread members [thread.thread.member]
     * C++11 standard (ISO/IEC 14882:2011):
     * 30.3.1.5 thread members [thread.thread.member]

See also
   get_id returns the id of the thread
          (public member function)
   join waits for the thread to finish its execution
          (public member function)
   detach permits the thread to execute independently from the thread handle
          (public member function)