output-line-buffered-or-packet-buffered.md

Output line-buffered or packet-buffered

"-l" option is used to specify output line-buffered. On Unix-like Operating Systems, setvbuf() or setlinebuf() will be used (code is here):

		......
		case 'l':
#ifdef _WIN32
			/*
			 * _IOLBF is the same as _IOFBF in Microsoft's C
			 * libraries; the only alternative they offer
			 * is _IONBF.
			 *
			 * XXX - this should really be checking for MSVC++,
			 * not _WIN32, if, for example, MinGW has its own
			 * C library that is more UNIX-compatible.
			 */
			setvbuf(stdout, NULL, _IONBF, 0);
#else /* _WIN32 */
#ifdef HAVE_SETLINEBUF
			setlinebuf(stdout);
#else
			setvbuf(stdout, NULL, _IOLBF, 0);
#endif
#endif /* _WIN32 */
			break;
		......

tcpdump can also output packet-buffered through "-U/--packet-buffered" option and call pcap_dump_flush API.