using std::cout in multiple threads

Question

I write a simple program for testing Thread in c++11 but std::cout doesnt work as I expect.

class Printer
{
public:
    void exec()
    {
               


        

Answer 1

I'm sharing the trick from Nicolás given in this question that I find to be more elegant than Howard Hinnant implementation. The idea is to create a temporary ostringstream object and put the protection code on the destructor.

/** Thread safe cout class
  * Exemple of use:
  *    PrintThread{} << "Hello world!" << std::endl;
  */
class PrintThread: public std::ostringstream
{
public:
    PrintThread() = default;

    ~PrintThread()
    {
        std::lock_guard guard(_mutexPrint);
        std::cout << this->str();
    }

private:
    static std::mutex _mutexPrint;
};

std::mutex PrintThread::_mutexPrint{};

You can then use it as a regular std::cout, from any thread:

PrintThread{} << "val = " << 33 << std::endl;

The object collect data as a regular std::ostringstream. As soon the coma is reached, the object is destroyed and flush all collected information.