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std::basic_ostream::flush

From cppreference.com
basic_ostream& flush();

Writes uncommitted changes to the underlying output sequence.

If rdbuf() is a null pointer, does nothing

Otherwise, constructs a sentry object which checks the stream for errors and flushes the tie()'d output streams. If the sentry object returns false, does nothing (since C++11)

Otherwise, calls rdbuf()->pubsync(). If the call returns -1, calls setstate(badbit).

Contents

[edit] Parameters

(none)

[edit] Return value

*this

[edit] Exceptions

May throw std::ios_base::failure if exceptions()&badbit!=0.

[edit] Example

#include <thread>
#include <iostream>
#include <chrono>
void f()
{
    std::cout << "Output from thread...";
    std::this_thread::sleep_for(std::chrono::seconds(2));
    std::cout << "...thread calls flush()\n";
    std::cout.flush();
}
 
int main()
{
    std::thread t1(f);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::clog << "Output from main\n";
    t1.join();
}

Output:

Output from main
Output from thread.....thread calls flush()

[edit] See also

synchronizes with the underlying storage device
(public member function of std::basic_istream) [edit]
flushes the output stream
(function template)
outputs '\n' and flushes the output stream
(function template)