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The cfgetispeed(), cfsetispeed(), cfgetospeed(), cfsetospeed() and cfsetspeed() functions are provided for getting and setting the baud rate values in the termios structure. The effects of the functions on the terminal as described below do not become effective, nor are all errors detected, until the tcsetattr() function is called. Certain values for baud rates set in the termios structure and passed to tcsetattr() have special meanings. These are discussed in the portion of the manual page that describes the tcsetattr() function.
#define B0 0 #define B50 50 #define B75 75 #define B110 110 #define B134 134 #define B150 150 #define B200 200 #define B300 300 #define B600 600 #define B1200 1200 #define B1800 1800 #define B2400 2400 #define B4800 4800 #define B9600 9600 #define B19200 19200 #define B38400 38400 #ifndef _POSIX_SOURCE #define EXTA 19200 #define EXTB 38400 #endif /*_POSIX_SOURCE */
The cfgetispeed() function returns the input baud rate in the termios structure referenced by tp.
The cfsetispeed() function sets the input baud rate in the termios structure referenced by tp to speed.
The cfgetospeed() function returns the output baud rate in the termios structure referenced by tp.
The cfsetospeed() function sets the output baud rate in the termios structure referenced by tp to speed.
The cfsetspeed() function sets both the input and output baud rate in the termios structure referenced by tp to speed.
Upon successful completion, the functions cfsetispeed(), cfsetospeed(), and cfsetspeed() return a value of 0. Otherwise, a value of -1 is returned and the global variable errno is set to indicate the error.
In all the functions, although fd is an open file descriptor, the functions affect the underlying terminal file, not just the open file description associated with the particular file descriptor.
The cfmakeraw() function sets the flags stored in the termios structure to a state disabling all input and output processing, giving a "raw I/O path", while the cfmakesane() function sets them to a state similar to those of a newly created terminal device. It should be noted that there is no function to reverse this effect. This is because there are a variety of processing options that could be re-enabled and the correct method is for an application to snapshot the current terminal state using the function tcgetattr(), setting raw or sane mode with cfmakeraw() or cfmakesane() and the subsequent tcsetattr(), and then using another tcsetattr() with the saved state to revert to the previous terminal state.
The tcgetattr() function copies the parameters associated with the terminal referenced by fd in the termios structure referenced by tp. This function is allowed from a background process, however, the terminal attributes may be subsequently changed by a foreground process.
The tcsetattr() function sets the parameters associated with the terminal from the termios structure referenced by tp. The action argument is created by or'ing the following values, as specified in the include file <termios.h>.
|The change occurs immediately.|
|The change occurs after all output written to fd has been transmitted to the terminal. This value of action should be used when changing parameters that affect output.|
|The change occurs after all output written to fd has been transmitted to the terminal. Additionally, any input that has been received but not read is discarded.|
|If this value is or'ed into the action value, the values of the c_cflag, c_ispeed, and c_ospeed fields are ignored.|
The 0 baud rate is used to terminate the connection. If 0 is specified as the output speed to the function tcsetattr(), modem control will no longer be asserted on the terminal, disconnecting the terminal.
If zero is specified as the input speed to the function tcsetattr(), the input baud rate will be set to the same value as that specified by the output baud rate.
If tcsetattr() is unable to make any of the requested changes, it returns -1 and sets errno. Otherwise, it makes all of the requested changes it can. If the specified input and output baud rates differ and are a combination that is not supported, neither baud rate is changed.
Upon successful completion, the functions tcgetattr() and tcsetattr() return a value of 0. Otherwise, they return -1 and the global variable errno is set to indicate the error, as follows:
|The fd argument to tcgetattr() or tcsetattr() was not a valid file descriptor.|
|The tcsetattr() function was interrupted by a signal.|
|The action argument to the tcsetattr() function was not valid, or an attempt was made to change an attribute represented in the termios structure to an unsupported value.|
|The file associated with the fd argument to tcgetattr() or tcsetattr() is not a terminal.|
|TCSETATTR (3)||January 2, 1994|
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|“||One of the advantages of using UNIX to teach an operating systems course is the sources and documentation will easily fit into a student's briefcase.||”|
|— John Lions|