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(libc.info)Pseudo-Terminal Pairs

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Opening a Pseudo-Terminal Pair
------------------------------

   These functions, derived from BSD, are available in the separate
`libutil' library, and declared in `pty.h'.

 - Function: int openpty (int *AMASTER, int *ASLAVE, char *NAME, struct
          termios *TERMP, struct winsize *WINP)
     This function allocates and opens a pseudo-terminal pair,
     returning the file descriptor for the master in *AMASTER, and the
     file descriptor for the slave in *ASLAVE.  If the argument NAME is
     not a null pointer, the file name of the slave pseudo-terminal
     device is stored in `*name'.  If TERMP is not a null pointer, the
     terminal attributes of the slave are set to the ones specified in
     the structure that TERMP points to (Note: Terminal Modes).
     Likewise, if the WINP is not a null pointer, the screen size of
     the slave is set to the values specified in the structure that
     WINP points to.

     The normal return value from `openpty' is 0; a value of -1 is
     returned in case of failure.  The following `errno' conditions are
     defined for this function:

    `ENOENT'
          There are no free pseudo-terminal pairs available.

     *Warning:* Using the `openpty' function with NAME not set to
     `NULL' is *very dangerous* because it provides no protection
     against overflowing the string NAME.  You should use the `ttyname'
     function on the file descriptor returned in *SLAVE to find out the
     file name of the slave pseudo-terminal device instead.

 - Function: int forkpty (int *AMASTER, char *NAME, struct termios
          *TERMP, struct winsize *WINP)
     This function is similar to the `openpty' function, but in
     addition, forks a new process (Note: Creating a Process) and
     makes the newly opened slave pseudo-terminal device the
     controlling terminal (Note: Controlling Terminal) for the child
     process.

     If the operation is successful, there are then both parent and
     child processes and both see `forkpty' return, but with different
     values: it returns a value of 0 in the child process and returns
     the child's process ID in the parent process.

     If the allocation of a pseudo-terminal pair or the process creation
     failed, `forkpty' returns a value of -1 in the parent process.

     *Warning:* The `forkpty' function has the same problems with
     respect to the NAME argument as `openpty'.