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.Dd July 2, 2024
.Dt PTSNAME 3C
.Os
.Sh NAME
.Nm ptsname ,
.Nm ptsname_r
.Nd get the name of the subsidiary device of a pseudo-terminal
.Sh SYNOPSIS
.In stdlib.h
.Ft char *
.Fo ptsname
.Fa "int fildes"
.Fc
.Ft int
.Fo ptsname_r
.Fa "int fildes"
.Fa "char *name"
.Fa "size_t namelen"
.Fc
.Sh DESCRIPTION
The
.Fn ptsname
function returns the name of the pseudo-terminal subsidiary device associated
with a pseudo-terminal manager device.
The
.Fa fildes
argument is a file descriptor returned from a successful open of the
pseudo-terminal manager device; e.g., by calling
.Xr posix_openpt 3C
or by performing an
.Xr open 2
of the
.Xr ptm 4D
device.
.Pp
The
.Fn ptsname
function returns a pointer to a string containing the null-terminated
path name of the subsidiary device.
This string is of the form
.Pa /dev/pts/N ,
where
.Sy N
is a non-negative integer.
Callers should generally assume that a subsequent call to
.Fn ptsname
will overwrite the returned buffer.
POSIX does not require that the interface be thread-safe.
While a per-thread buffer is currently being used, that should not be relied
upon by portable applications and is not a system guarantee.
.Pp
The
.Fn ptsname_r
function behaves similarly to the
.Fn ptsname
function, but rather than use a thread-specific buffer, stores the name of the
pseudo-terminal subsidiary device of
.Fa fildes
in
.Fa name .
The size of
.Fa name
is indicated by
.Fa namelen .
If the buffer is not large enough, then the function will fail with
.Er ERANGE .
The name's length will not exceed
.Brq TTY_NAME_MAX ,
which can be determined at runtime by calling
.Xr sysconf 3C
with the name
.Dv _SC_TTY_NAME_MAX .
.Sh RETURN VALUES
Upon successful completion, the
.Fn ptsname
function returns a pointer to a string which is the name of the pseudo-terminal
subsidiary device.
This value points to a static data area that is overwritten by each call to
.Fn ptsname
by the same thread.
Otherwise,
.Dv NULL
is returned and
.Va errno
is set to indicate the error that occurred.
.Pp
Upon successful completion, the
.Fn ptsname_r
function will return
.Sy 0
and
.Fa name
will be filled in with the subsidiary device's name.
Otherwise, an error number will be returned.
.Sh ERRORS
The
.Fn ptsname
and
.Fn ptsname_r
functions will fail if:
.Bl -tag -width Er
.It Er EBADF
The file descriptor,
.Fa fildes ,
does not refer to a valid file descriptor.
.It Er EINVAL
The file descriptor,
.Fa fildes ,
does not refer to a manager pseudo-terminal device.
.Pp
For the
.Fn ptsname_r
function,
.Fa name
is a
.Dv NULL
pointer.
.It Er ENOTTY
The file descriptor,
.Fa fildes ,
does not refer to a manager pseudo-terminal device.
.It Er ERANGE
For the
.Fn ptsname_r
function, the buffer
.Fa name 's
size as indicated by
.Fa namelen
was too small to hold the actual subsidiary device's name.
.El
.Sh INTERFACE STABILITY
.Sy Committed
.Sh MT LEVEL
The
.Fn ptsname
function is
.Sy Safe .
.Pp
The
.Fn ptsname_r
function is
.Sy MT-Safe .
.Sh SEE ALSO
.Xr open 2 ,
.Xr grantpt 3C ,
.Xr posix_openpt 3C ,
.Xr ttyname 3C ,
.Xr unlockpt 3C ,
.Xr ptm 4D ,
.Xr pts 4D ,
.Xr attributes 7 ,
.Xr standards 7