About printf () and fflush ()

When printf () is used for output, it is first output to the buffer and then sent from the buffer to the screen. Under what circumstances will the buffer content be sent to the screen? 1. Use fflush (stdout) to force refresh. 2. the buffer zone is full. 3. scanf () refreshes the buffer first when it needs to retrieve data in the buffer zone. 4. When \ n and \ r enter the buffer zone. 5. When the thread ends, if the thread also contains printf (...); 6, when the program ends.

# Include <stdio. h>
# Include <stdlib. h>
Int main ()
{
Int I = 89;
Int X;
Printf ("-------------- \ n"); // output ----------- without outputting 89 immediately;
Printf ("% d", I); // after this statement, add fflush (stdout); then the output will be 89 immediately
Sleep (5 );
Scanf ("% d", & X); // output the 89 to the screen after 5 seconds.
Return 0;
}

In addition, when the fclose function closes a file, the function writes the file content that has not been written back to the disk in the memory to the disk. If the fclose function is not called, wait until the buffer in the memory is filled up and the system writes the content back to the disk.