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#### 17.8.2 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, const struct termios *termp, const 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 (see 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, const struct termios *termp, const struct winsize *winp)

> This function is similar to the `openpty` function, but in addition, forks a new process (see Creating a Process) and makes the newly opened slave pseudo-terminal device the controlling terminal (see 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`.