C++ Primer Plus

Flushing the Output Buffer

Consider what happens as a program uses cout to send bytes on to the standard output. Because the ostream class buffers output handled by the cout object, output isn’t sent to its destination immediately. Instead, it accumulates in the buffer until the buffer is full. Then the program flushes the buffer, sending the contents on and clearing the buffer for new data. Typically, a buffer is 512 bytes or an integral multiple thereof. Buffering is a great time-saver when the standard output is connected to a file on a hard disk. After all, you don’t want a program to access the hard disk 512 times to send 512 bytes. It’s much more effective to collect 512 bytes in a buffer and write them to a hard disk in a single disk operation. ...