std::thread
- C++ course
- Advanced
- Lesson 19/83
- 5 min
Learn to create threads with std::thread.
std::thread
std::thread starts a separate execution thread. The syntax is std::thread t(func); where func is the function to run on the thread. The main thread continues while t runs on a separate flow.
To wait for the thread to finish call t.join();. Without join the program ends via std::terminate. detach leaves the thread in the background; you do not wait but cannot synchronize the result. Beginners should use join.
Thread function
A thread accepts any callable: a function, a lambda or a function object. Arguments are passed as std::thread t(func, arg1, arg2);. If the thread function returns void the result is lost; to get a value back use std::async.
The thread is independent of the main flow; it runs at the same time. If it touches shared data the data must be protected with a std::mutex. Otherwise a data race occurs and the behaviour is undefined. That is the topic of the next lesson.
Practice print_hello thread
Write void print_hello() with body std::cout << "Merhaba";. In main start it with std::thread t(print_hello); and wait with t.join();. Include the <thread> and <iostream> headers.
Starter code
#include <iostream>
#include <thread>
// Write the print_hello function
int main() {
// Start the thread and wait
return 0;
}Sample solution
#include <iostream>
#include <thread>
void print_hello() {
std::cout << "Merhaba";
}
int main() {
std::thread t(print_hello);
t.join();
return 0;
}Expected output
Merhaba
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does t.join() do?
std::thread t(func);
t.join();- Deletes the thread
- Stops the thread
- Waits for the thread to finish Correct answer
- Starts a new thread
Explanation: join blocks the main flow until the thread finishes.
2 Complete the join line
std::thread t(print_hello);
____;std::thread t(print_hello);
t.join;Explanation: t.join() waits for the thread.
3 Match each expression to its role
| Term | Meaning |
|---|---|
std::thread t(func) |
Start a thread |
t.join() |
Wait and merge |
t.detach() |
Leave in background |
#include <thread> |
Header file |