tcdrain - wait for transmission of output

Syntax	#include <termios.h> int tcdrain (int fildes);
Description	tcdrain() waits until all output written to the object specified by fildes is transmitted. The fildes argument is an open file descriptor associated with a terminal. Any attempts to use tcdrain() from a process which is a member of a background process group on a fildes associated with its controlling terminal, will cause the process group to be sent a SIGTTOU signal. If the calling process is blocking or ignoring SIGTTOU signals, the process is allowed to perform the operation, and no signal is sent.
Return val.	0 -1	if successful. If an error occurs. errno is set to indicate the error.
Errors	tcdrain() will fail if:
	EBADF	fildes is not a valid file descriptor.
	EINTR	A signal was caught during the tcdrain() system call.
	Extension
	EINVAL	An attempt was made to access a BS2000 file. (End)
	EIO	The process group of the writing process is orphaned, and the writing process is not ignoring or blocking SIGTTOU.
	ENOTTY	The file associated with fildes is not a terminal.
Notes	tcdrain() has no effect on block-mode terminals.
See also	tcflush(), termios.h, unistd.h, section “General terminal interface”.