JuniorTheoryVery common

What happens if a `std::thread` is destroyed without `join` or `detach`?

C++

#include <iostream>
#include <thread>

void greet() {
    std::cout << "hi\n";
}

int main() {
    std::thread t(greet);
}

The program is aborted by std::terminate: t was neither joined nor detached

Expecting the destructor to join: std::jthread does that, but a std::thread destroyed without join() or detach() calls std::terminate.
Expecting an automatic detach(): a silently detached thread could outlive the data it uses, which is why the destructor calls std::terminate instead.

JuniorTheoryVery common

C++

#include <iostream>
#include <thread>

void greet() {
    std::cout << "hi\n";
}

int main() {
    std::thread t(greet);
}

The program is aborted by std::terminate: t was neither joined nor detached

Expecting the destructor to join: std::jthread does that, but a std::thread destroyed without join() or detach() calls std::terminate.
Expecting an automatic detach(): a silently detached thread could outlive the data it uses, which is why the destructor calls std::terminate instead.

What happens if a std::thread is destroyed without join or detach?