.\" $NetBSD: ptsname.3,v 1.13 2022/01/02 03:46:40 uwe Exp $
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.\" by Christos Zoulas.
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.Dd January 2, 2022
.Dt PTSNAME 3
.Os
.Sh NAME
.Nm ptsname ,
.Nm ptsname_r
.Nd get the pathname of the slave pseudo-terminal device
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft char *
.Fn ptsname "int masterfd"
.Ft int
.Fn ptsname_r "int masterfd" "char *buf" "size_t buflen"
.Sh DESCRIPTION
The
.Fn ptsname
function returns the pathname of the slave pseudo-terminal device
that corresponds to the master pseudo-terminal device associated with
.Fa masterfd .
The
.Fn ptsname
function is not reentrant or thread-safe.
.Pp
The
.Fn ptsname_r
function
places the pathname of the slave pseudo-terminal device that corresponds
to the master pseudo-terminal device associated with
.Fa masterfd
int the
.Fa buf
argument copying up to
.Fa buflen
characters.
The
.Fa buf
is always
.Dv NUL
terminated.
.Sh RETURN VALUES
If successful,
.Fn ptsname
returns a pointer to a nul-terminated string containing the pathname
of the slave pseudo-terminal device.
If an error occurs
.Fn ptsname
will return
.Dv NULL
and
.Va errno
is set to indicate the error.
.Pp
If successful,
.Fn ptsname_r
places a nul-terminated string containing the pathname
of the slave pseudo-terminal device
in
.Fa buf
and returns
.Dv 0 .
If an error occurs
.Fn ptsname_r
will return
an error number indicating what went wrong.
.Sh ERRORS
The
.Fn ptsname
and
.Fn ptsname_r
functions will fail if:
.Bl -tag -width Er
.It Bq Er EACCESS
the corresponding pseudo-terminal device could not be accessed.
.It Bq Er EBADF
.Fa masterfd
is not a valid descriptor.
.It Bq Er EINVAL
.Fa masterfd
is not associated with a master pseudo-terminal device.
.El
.Pp
In addition the
.Fn ptsname_r
function
will return:
.Bl -tag -width Er
.It Bq Er EINVAL
the
.Fa buf
argument is
.Dv NULL .
.It Bq Er ERANGE
the name of the pseudo-terminal is longer than
.Fa bufsiz
characters plus the terminating
.Dv NUL .
.El
.Sh NOTES
The error returns of
.Fn ptsname
are a
.Nx
extension.
The
.Fn ptsname
function is equivalent to:
.Bd -literal
	static struct ptmget pm;
	return ioctl(masterfd, TIOCPTSNAME, &pm) == -1 ? NULL : pm.sn;
.Ed
.Pp
Both the
.Fn ptsname
and
.Fn ptsname_r
functions will also return the name of the slave pseudo-terminal if a file
descriptor to the slave pseudo-terminal is passed to
.Fa masterfd .
.Pp
This is a convenient extension because it allows one to use the file descriptor
obtained by
.Xr open 2
.Pa /dev/tty
to obtain the name of the pseudo-terminal for the current process.
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr open 2 ,
.Xr grantpt 3 ,
.Xr posix_openpt 3 ,
.Xr unlockpt 3
.Sh STANDARDS
The
.Fn ptsname
function conforms to
.St -p1003.1-2001 .
Its first release was in
.St -xpg4.2 .