Initialization for Use of Termcap

Before starting to output commands to a terminal using termcap, an application program should do two things:

• Initialize various global variables which termcap library output functions refer to. These include PC and ospeed for padding (see section Performing Padding with tputs) and UP and BC for cursor motion (see section tgoto).
• Tell the kernel to turn off alteration and padding of horizontal-tab characters sent to the terminal.

To turn off output processing in Berkeley Unix you would use ioctl with code TIOCLSET to set the bit named LLITOUT, and clear the bits ANYDELAY using TIOCSETN. In POSIX or System V, you must clear the bit named OPOST. Refer to the system documentation for details.

If you do not set the terminal flags properly, some older terminals will not work. This is because their commands may contain the characters that normally signify newline, carriage return and horizontal tab--characters which the kernel thinks it ought to modify before output.

When you change the kernel's terminal flags, you must arrange to restore them to their normal state when your program exits. This implies that the program must catch fatal signals such as SIGQUIT and SIGINT and restore the old terminal flags before actually terminating.

Modern terminals' commands do not use these special characters, so if you do not care about problems with old terminals, you can leave the kernel's terminal flags unaltered.

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