Linux uses the tcgetattr function and the tcsetattr function control terminal

To facilitate obtaining and modifying terminal parameters through a program, Linux also provides tcgetattr and tcsetattr functions. Tcgetattr is used to obtain terminal-related parameters, while the tcsetattr function is used to set terminal parameters. The specific information of these two functions is shown in table 6.2.

Table 6.2 tcgetattr and tcsetattr Functions

Header file	<Termios. h> <Unistd. h>
Function Form	Int tcgetattr (int fd, struct termios * termios_p ); Int tcsetattr (int fd, int optional_actions, const struct termios * termios_p );
Return Value	Successful	Failed	Whether to set errno
	0	−1	Yes

Description: The tcgetattr function is used to obtain terminal-related parameters. The FD parameter is the file descriptor of the terminal, and the returned results are stored in the termios struct. This struct generally includes the following members:

Tcflag_t c_iflag;
Tcflag_t c_oflag;
Tcflag_t c_cflag;
Tcflag_t c_lflag;
Cc_t c_cc [NCCs];

Its significance is as follows:

C_iflag: indicates the input mode and controls the input mode of the terminal. The specific parameters are shown in table 6.3.

Table 6.3 c_iflag parameter table

Key Value	Description
Ignbrk	Ignore break key input
Brkint	If ignbrk is set, the break key input is ignored. If brkint is set, SIGINT interruption occurs.
Ignpar	Ignore parity errors
Parmrk	Incorrect ID parity
Inpck	Allow input parity
Istrip	Remove 8th characters
Inlcr	Convert input NL (line feed) to Cr (Press ENTER)
Igncr	Ignore input carriage return
Icrnl	Convert the input carriage return to line feed (if igncr is not set)
Iuclc	Converts an input uppercase character to a lowercase character (non-POSIX)
Ixon	Allow control of the Xon/xoff stream during Input
Ixany	Output that will restart and stop when any character is entered
Ixoff	Allow control of the Xon/xoff stream during Input
Imaxbel	When the input queue is full, the system starts to ring the bell. in Linux, the system uses this parameter and considers that this parameter has always been set.

C_oflag: the output mode flag that controls the terminal output mode. The specific parameters are shown in table 6.4.

Table 6.4 c_oflag Parameters

Key Value	Description
Opost	Output after processing
Olcuc	Converts lowercase characters to uppercase (non-POSIX)
Onlcr	Convert the input NL (line feed) to Cr (Press ENTER) and NL (line feed)
Ocrnl	Convert input Cr (Press ENTER) to Nl (line feed)
Onocr	The first line does not output a carriage return.
Onlret	No carriage return
Ofill	Send fill characters to delay terminal output
Ofdel	Use the del of the ASCII code as the filling character. If this parameter is not set, the filling character will be NUL ('/0') (non-POSIX)
Nldly	Line feed output delay, which can be nl0 (no delay) or nl1 (0.1 s delay)
Crdly	Carriage Return delay, value range: Cr0, CR1, CR2
Tabdly	Latency of horizontal tab output. Values: tab0, tab1, tab2, and tab3
Bsdly	Space output delay, which can be bs0 or BS1
Vtdly	Vertical tab output latency, which can be vt0 or vt1
Ffdly	Page feed delay, which can be ff0 or ff1

C_cflag: Control Mode flag that specifies the hardware control information of the terminal. The specific parameters are shown in table 6.5.

Table 6.5 c_oflag Parameters

Key Value	Description
Cbaud	Baud rate (4 + 1 bits) (non-POSIX)
Cbaudex	Additional baud rate (1 bit) (non-POSIX)
Csize	Length, value range: cs5, CS6, cs7, or cs8
Cstopb	Set two stop bits
Cread	Use Receiver
Parenb	Use parity
Parodd	Use parity for input and even for output
Hupcl	Suspended when the device is disabled
Clocal	Ignore modem line status
Crtscts	Use RTS/CTS Stream Control

C_lflag: indicates the local mode flag and controls the terminal editing function. The specific parameters are shown in table 6.6.

Table 6.6 c_lflag Parameters

Key Value	Description
Isig	When intr, quit, susp, or dsusp is input, corresponding signals are generated.
Icanon	Use standard input mode
Xcase	When both icanon and xcase are set, the terminal only uses uppercase letters. If only xcase is set, the input characters are converted to lowercase characters, unless the characters use escape characters (non-POSIX, and Linux does not support this parameter)
Echo	Show input characters
Echoe	If icanon is set at the same time, erase deletes the entered characters and werase deletes the entered words.
Echok	If icanon is set at the same time, kill will delete the current row
Echonl	If icanon is set at the same time, even if ECHO is not set, the line break is still displayed.
Echoprt	If echo and icanon are both set, the printed characters (non-POSIX) are deleted)
Tostop	Send sigttou signal to the background

C_cc [NCCs]: A control character used to save special characters in the terminal driver, such as the input Terminator. C_cc defines the control characters shown in table 6.7.

Table 6.7 control characters supported by c_cc

Macro	Description	Macro	Description
Vintr	Interrupt characters	Veol	Additional end-of-file characters
Vquit	Quit character	Vtime	Timeout value for reading in non-standard mode
Verase	Erase characters	Vstop	Stop character
Vkill	Kill characters	Vstart	Start character
Veof	End-of-file character	Vsusp	Suspend character
Vmin	Minimum number of characters for reading in non-standard mode

The tcsetattr function is used to set terminal parameters. The FD parameter is the terminal file descriptor that is opened. The optional_actions parameter is used to control the time when the modification takes effect. The termios_p struct stores the parameters to be modified.
Optional_actions can take the following values.
Tcsanow: changes the attributes immediately after data transmission is completed.
Tcsadrain: the attribute is changed only after all data transmission ends.
Tcsaflush: the attribute is changed only when the input and output buffer is cleared.

Error message:
Ebadf: invalid file descriptor.
Eintr: the call to the tcsetattr function is interrupted by the signal.
Einval: The optional_actions parameter uses an invalid value or an invalid value in the termios parameter.
Enctty: Non-terminal file descriptor.

Instance drill:
The program p6.2.c changes the terminal control character from Ctrl + D to Ctrl + G ". First, the program calls the tcgetattr function to obtain the termios information of the standard input, and changes the c_cc [veof] control character in the termios struct to 0x07 (CTRL + G). Then, use the tcsetattr function to set the modified termios parameter to the terminal. The Code is as follows:

// P6.2.c terminal control character modification example # include <stdio. h> # include <termios. h> # include <unistd. h> # include <errno. h> Int main (void) {// term is used to store the obtained terminal parameter information struct termios term; int err; // Obtain the standard input terminal parameters and save the obtained information in the term variable if (tcgetattr (stdin_fileno, & term) =-1) {perror ("cannot get standard input description"); return 1 ;} // Modify the ending control character of the obtained terminal information. Term. c_cc [veof] = (cc_t) 0x07; // Use the tcsetattr function to set the modified terminal parameters to the standard input. // err is used to save the call result of the function. Err = tcsetattr (stdin_fileno, tcsaflush, & term ); // If err is-1 or an eintr error occurs (function execution is interrupted by signal), // provide the relevant error message if (ERR =-1 & err = eintr) {perror ("failed to change EOF character"); return 1 ;} Return 0 ;}

Use GCC to compile the p6.2.c program and obtain the executable program p6.2. Before executing the p6.2 program, press Ctrl + D to end the terminal. After executing the p6.2 program, pressing "Ctrl + D" has no effect, and entering "Ctrl + G" implements the original "Ctrl + D" function.

Address: http://blog.csdn.net/xuefu2008/article/details/4662368