_IOLBF
setvbuf(stdout, NULL, _IOLBF, BUFSIZ);
case _IOLBF:
setvbuf(stdout, NULL, _IOLBF, 0);
setvbuf(stdout, NULL, _IOLBF, 0);
setvbuf(stdout, NULL, _IOLBF, 0);
setvbuf(stderr, NULL, _IOLBF, 0);