C++ buffered stream IO

Question

I understand that by default all stream IO supported by C++ is buffered.

This means that data to be output is put into a buffer till it is full and then sent to the

Answer 1

Try the following code:

int main()
{
    for( int i =0 ; i < 10; i ++ )
    {
        cout << i << " ";
        cerr << i << " ";
    }
}

The buffered output is usually flushed with the destruction of the stream object, so the code above will print (not always, ofc, but it does for me with gcc 4.6.3)

0 1 2 3..9
0 1 2 3..9

instead of

0 0 1 1 2 2 3 3 .... 9 9 

Because the unbuffered cerr is printed right away (first sequence) , and buffered cout is printed in the end of main().