cfsetspeed(3)              Library Functions Manual              cfsetspeed(3)

NAME
       cfgetospeed, cfgetispeed, cfsetispeed, cfsetospeed, cfsetspeed - get
       and set line speed

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <termios.h>

       speed_t cfgetispeed(const struct termios *termios_p);
       speed_t cfgetospeed(const struct termios *termios_p);

       int cfsetispeed(struct termios *termios_p, speed_t speed);
       int cfsetospeed(struct termios *termios_p, speed_t speed);

       #define _DEFAULT_SOURCE  /* See feature_test_macros(7) */
       #include <termios.h>

       int cfsetspeed(struct termios *termios_p, speed_t speed);

DESCRIPTION
       The baud rate functions are provided for getting and setting the values
       of the input and output baud rates in the termios structure.  The new
       values do not take effect until tcsetattr(3) is successfully called.

       Setting the speed to B0 instructs the modem to "hang up".  The actual
       bit rate corresponding to B38400 may be altered with setserial(8);
       doing so is discouraged as it may break other applications later trying
       to use the same serial port.

       The input and output baud rates are stored in the termios structure.

       cfgetospeed() returns the output baud rate stored in the termios
       structure pointed to by termios_p.

       cfsetospeed() sets the output baud rate stored in the termios structure
       pointed to by termios_p to speed, which must be one of these constants:

              B0
              B50
              B75
              B110
              B134
              B150
              B200
              B300
              B600
              B1200
              B1800
              B2400
              B4800
              B9600
              B19200
              B38400
              B57600
              B115200
              B230400
              B460800
              B500000
              B576000
              B921600
              B1000000
              B1152000
              B1500000
              B2000000

       These constants are additionally supported on the SPARC architecture:

              B76800
              B153600
              B307200
              B614400

       These constants are additionally supported on non-SPARC architectures:

              B2500000
              B3000000
              B3500000
              B4000000

       Due to differences between architectures, portable applications should
       check if a particular Bnnn constant is defined prior to using it.

       The zero baud rate, B0, is used to terminate the connection.  If B0 is
       specified, the modem control lines shall no longer be asserted.
       Normally, this will disconnect the line.  CBAUDEX is a mask for the
       speeds beyond those defined in POSIX.1 (57600 and above).  Thus, B57600
       & CBAUDEX is nonzero.

       Setting the baud rate to a value other than those defined by Bnnn
       constants is possible via the TCSETS2 ioctl; see ioctl_tty(2).

       cfgetispeed() returns the input baud rate stored in the termios
       structure.

       cfsetispeed() sets the input baud rate stored in the termios structure
       to speed, which must be specified as one of the Bnnn constants listed
       above for cfsetospeed().  If the input baud rate is set to the literal
       constant 0 (not the symbolic constant B0), the input baud rate will be
       equal to the output baud rate.

       cfsetspeed() takes the same arguments as cfsetispeed(), and sets both
       input and output speed.

RETURN VALUE
       cfgetispeed() returns the input baud rate stored in the termios
       structure.

       cfgetospeed() returns the output baud rate stored in the termios
       structure.

       All other functions return:

       0      on success.

       -1     on failure and set errno to indicate the error.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |cfgetispeed (), cfgetospeed (), cfsetispeed | Thread safety | MT-Safe |
       |(), cfsetospeed (), cfsetspeed ()           |               |         |
       +--------------------------------------------+---------------+---------+
VERSIONS
       UNIX V7 and several later systems have a list of baud rates where after
       the values B0 through B9600 one finds the two constants EXTA, EXTB
       ("External A" and "External B").  Many systems extend the list with
       much higher baud rates.

STANDARDS
       cfgetispeed()
       cfgetospeed()
       cfsetispeed()
       cfsetospeed()
              POSIX.1-2008.

       cfsetspeed()
              BSD.

HISTORY
       cfgetispeed()
       cfgetospeed()
       cfsetispeed()
       cfsetospeed()
              POSIX.1-2001.

       cfsetspeed()
              4.4BSD.

SEE ALSO
       speed_t(3type), termios(3type)

Linux man-pages 6.19              2026-07-02                     cfsetspeed(3)