std:: unitbuf, std:: nounitbuf

Enables or disables automatic flushing of the output stream after any output operation. Has no effect on input.

This is an I/O manipulator, it may be called with an expression such as out << std :: unitbuf for any out of type std::basic_ostream or with an expression such as in >> std :: unitbuf for any in of type std::basic_istream .

Notes

Flushing is performed in the destructor of the std::basic_ostream::sentry object, which calls str. rdbuf ( ) - > pubsync ( ) if str. flags ( ) & std:: ios_base :: unitbuf is true .

The standard output objects std::cerr and std::wcerr have their unitbuf bit set by default.

Parameters

Return value

str (reference to the stream after manipulation).

Example

#include <chrono>
#include <iostream>
 
template<typename Diff>
void log_progress(Diff d)
{
    std::cout << std::chrono::duration_cast<std::chrono::milliseconds>(d)
              << " ... ";
}
 
int main()
{
    volatile int sink = 0;
    std::cout << std::unitbuf; // enable automatic flushing
 
    const auto start = std::chrono::high_resolution_clock::now();
    for (int j = 0; j < 5; ++j)
    {
        for (int n = 0; n < 10000; ++n)
            for (int m = 0; m < 20000; ++m)
                sink += m * n; // do some work
        log_progress(std::chrono::high_resolution_clock::now() - start);
    }
    std::cout << '\n';
}

571ms ... 1146ms ... 1722ms ... 2294ms ... 2865ms ...

See also