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The All-in-One Guide to C++20

Output streams with std::cout

Understand how to achieve thread-safe, synchronized output in C++20 using std::cout. Explore the challenges of unsynchronized access, how C++11 guarantees atomic character output, and how C++20 introduces simpler synchronization with std::basic_osyncstream to prevent interleaving and race conditions.

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🔑 Compiler support for synchronized output streams

At the end of 20202020, only GCC 11 supports synchronized output streams.

Non-synchronized access to std::cout

What happens when you write without synchronization to std::cout?

C++
#include <chrono>
#include <iostream>
#include <thread>
class Worker{
public:
    Worker(std::string n):name(n) {};
        void operator() (){
            for (int i = 1; i <= 3; ++i) {
                // begin work
                std::this_thread::sleep_for(std::chrono::milliseconds(200));
                // end work
                std::cout << name << ": " << "Work " << i << " done !!!" << '\n';
            }
        }
private:
    std::string name;
};
int main() {
    std::cout << '\n';
    
    std::cout << "Boss: Let's start working.\n\n";
  
    std::thread herb= std::thread(Worker("Herb"));
    std::thread andrei= std::thread(Worker("  Andrei"));
    std::thread scott= std::thread(Worker("    Scott"));
    std::thread bjarne= std::thread(Worker("      Bjarne"));
    std::thread bart= std::thread(Worker("        Bart"));
    std::thread jenne= std::thread(Worker("          Jenne"));
    
    
    herb.join();
    andrei.join();
    scott.join();
    bjarne.join();
    bart.join();
    jenne.join();
    
    std::cout << "\n" << "Boss: Let's go home." << '\n';
    
    std::cout << '\n'; 
}

The boss has six workers (lines 26 - 31). Each worker has to take care of three ...