std::basic_ostream<CharT,Traits>:: flush

Writes uncommitted changes to the underlying output sequence. Behaves as an UnformattedOutputFunction .

If rdbuf() is a null pointer, the sentry object is not constructed.

Otherwise, after constructing and checking the sentry object, calls rdbuf ( ) - > pubsync ( ) . If the call returns - 1 , calls setstate ( badbit ) .

Parameters

(none)

Return value

* this

Exceptions

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

Example

#include <chrono>
#include <iostream>
#include <thread>
 
using namespace std::chrono_literals;
 
void f()
{
    std::cout << "Output from thread... ";
    for (int i{1}; i != 10; ++i)
    {
        std::this_thread::sleep_for(250ms);
        std::cout << i << ' ';
 
        // output three numbers at once;
        // the effect is observable only in real-time
        if (0 == (i % 3))
            std::cout.flush();
    }
    std::cout << std::endl; // flushes as well
}
 
int main()
{
    std::thread tr{f};
    std::this_thread::sleep_for(150ms);
    std::clog << "Output from main\n";
    tr.join();
}

Output from main
Output from thread... 1 2 3 4 5 6 7 8 9

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also