code compilation error using thread and mutex

[aligh]

I'm trying to learn the basics of threads, mutex and function objects.
Here's my test code trying to output "Hello" and "World" by two different threads every second.

#include <iostream>
#include <thread>
#include <mutex>

using namespace std;

mutex m;

struct Hello {
public:
    void operator()(){
        for(int i = 0; i < 10; i++) {
            this_thread::sleep_for(chrono::milliseconds{1000});
            unique_lock<mutex> lock {m};
            cout << "Hello ";
        }
    }
};

struct World {
public:
    void operator()(){
        for (int i = 0; i < 10; i++) {
            this_thread::sleep_for(chrono::milliseconds{1000});
            unique_lock<mutex> lock {m};
            cout << "World!" << "\n";
        }
    }
};

/*
 * 
 */
int main(int argc, char** argv) {
    thread t1 {Hello()};
    thread t2 {World()};
    
    t1.join();
    t2.join();
    return 0;
}

My code doesn't compile.

Here's my compiler version:

g++ (Ubuntu 7.4.0-1ubuntu1~18.04) 7.4.0

using "-g -std=c++14" argument I get the following error:

g++ -o dist/Debug/GNU-Linux/01 build/Debug/GNU-Linux/main.o
build/Debug/GNU-Linux/main.o: In function `std::thread::thread<Hello>(Hello&&)':
/usr/include/c++/7/thread:122: undefined reference to `pthread_create'
build/Debug/GNU-Linux/main.o: In function `std::thread::thread<World>(World&&)':
/usr/include/c++/7/thread:122: undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status

If that's of relevance, I'm using NetBeans IDE 11.0 on an Ubuntu 18.04.

Thanks!

[Repeater]

Try

g++ -g -pthread -std=c++14

https://gcc.gnu.org/onlinedocs/libstdc++/manual/using.html#manual.intro.using.flags

[aligh]

Thank you @Repeater!

Works perfectly.